IoT Devices - Maker and IOT Ideas

Simple Smart Light Controller

Adding a bit of automation to a certain area of the house can definitely help with saving energy. With this Simple Smart Light Controller, I aimed to do just that… Let me give you a tiny bit of context… Houses in SE Asia are built to some “questionable” standards and designs, and electrical installations are usually even more suspect… Our house is no exception. Being a rental, I do not want to go and make changes unless things are outright dangerous… Kitchens are usually a mixture of inside/outside areas, and this is where my device fits in…

The light in the outside kitchen consists of a simple bulb that the owner has routed into the house via an electrical flex cord, at least that was standard… But, due to laziness or just whatever, that cord was never terminated into a proper switch… He just added a plug. This is thus my opportunity to make life a bit easier for myself in that area. I could have opted for a standard switch, but then, automating this can take care of another problem… We constantly forget to switch that light off, as the plug is in a “strange place” that is not usually associated with the kitchen lights…

What I have thus come up with is a simple ESP8266-based solution with a single relay ( optically isolated from the board), as well as a few additional GPIO pins, just in case I want to hang some additional sensors onto this in the future.

The device should also be powered directly from the mains, as adding another external AC to DC adapter would definitely NOT do at all!

What is on the PCB

Lets look at the empty PCB, in order to understand better what is where on the board.

Starting on the Left Side, at the bottom corner, we have our mains voltage input, 220V or 110V, depending on where you live. That goes directly into U1, which is a AC-to-DC converter, providing 3.3v at 1A to the board. Note that I did not place a fuse directly on the board. I prefer to have an inline fuse on the line, which is also accessible from the enclosure.

A series of cutouts on the PCB provides additional mains isolation and also prevents mains voltage tracking towards other tracks in the event of a fault.
The Mains area also does not have a copper pour.

In the top left corner, towards the center, is a WAKE jumper. This is connected to GPIO16 and can be used to wake the ESP8266 from “deep sleep” if configured in the firmware.

Relay K1, and its screw terminal connector is in the bottom center of the board, with the relay contacts clearly labelled.

On the right of the PCB, we have the programming header, complete with Auto Flash and Reset circuitry, as well as manual Flash and Reset Buttons below that.

A 3×3 header connector follows, with access to 3.3v, Ground as well as 3 additional GPIO pins for other applications.

Finally, we have the relay control switch, with a few options to connect external switches, either on the 2.54mm header, or via wires soldered to the pads marked SW-A and SW-B

The populated PCB will thus make more sense if we look at the picture above now since we had a detailed look at it above…

Schematic_ESP8266-Smart-light-switch_2023-07-03 Download

The Schematic is made available at the link above.

Configuration and Software

This build was designed with ESPHome in mind, so we will focus on that there.
You can however very easily use standard Arduino/ESP8266 code to control this as well…

The YAML configuration for the device will be as follows: (note that this is quite simplified, as I am still fine-tuning the actual features that I require)

esphome:
  name: smart-switch-01
  friendly_name: SMART-SWITCH-01

esp8266:
  board: nodemcuv2
  restore_from_flash: true

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "hfYNn8KSbVq26rGkPOJo4yLj/d/WY7Hk0H3TmxlWZAU="

ota:
  password: "85ed2a8afcd61d0f4c65db7b92bdacc5"

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Smart-Switch-01 Fallback Hotspot"
    password: "XovAx4n1H1qT"

captive_portal:

text_sensor:
  - platform: wifi_info
    ip_address:
      name: IP Address
    ssid:
      name: SSID
    bssid:
      name: BSSID
    mac_address:
      name: Wifi MAC
    scan_results:
      name: WiFi Scan Results


sensor:
  - platform: adc
    pin: VCC
    name: "ESP8266 Chip Voltage"
    id: mcu_voltage
    unit_of_measurement: "V"
    device_class: "voltage"
    accuracy_decimals: 2
    update_interval: 60s
    entity_category: "diagnostic"
    
  - platform: wifi_signal
    name: "WiFi Signal Sensor"
    id: wifi_strength
    device_class: "signal_strength"
    unit_of_measurement: "dBm"
    update_interval: 240s
    entity_category: "diagnostic"

  - platform: copy # Reports the WiFi signal strength in %
    source_id: wifi_strength
    name: "WiFi Signal Strength"
    filters:
      - lambda: return min(max(2 * (x + 100.0), 0.0), 100.0);
    unit_of_measurement: "%"
    entity_category: "diagnostic"


light:
 # - platform: status_led
 #   pin: GPIO13
 #   id: status_indicator
 #   name: "ID Light"
    
  - platform: binary
    name: "Kitchen Outside Light"
    output: relay_01
    id: kitchen_light
    on_turn_on:
    - light.turn_on:
        id: slow_light
        effect: "Slow Pulse"
    

    on_turn_off:
    - light.turn_off: slow_light
    

  - platform: monochromatic
    id: slow_light
    output: light_status
    restore_mode: RESTORE_AND_OFF
    effects:
      - pulse:
          name: "Slow Pulse"
          # transition_length: 1s      # defaults to 1s
          update_interval: 2s

binary_sensor:
  - platform: gpio
    pin:
      number: GPIO5
      mode:
        input: true
        pullup: true
    id: kitchen_light_toggle
    filters:
      - delayed_on: 200ms
      - delayed_off: 200ms
    on_press:
      then:
        - light.toggle: kitchen_light
  - platform: status
    name: "Kitchen Light Controller"
     
switch:
  - platform: restart
    name: "Restart Device"

# Relay output
output:
  - platform: gpio
    id: relay_01
    pin: GPIO4
    inverted: true
  - platform: esp8266_pwm
    id: light_status
    pin: GPIO12

Manufacturing the PCB

I choose PCBWay for my PCB manufacturing. Why? What makes them different from the rest?

PCBWay‘s business goal is to be the most professional PCB manufacturer for prototyping and low-volume production work in the world. With more than a decade in the business, they are committed to meeting the needs of their customers from different industries in terms of quality, delivery, cost-effectiveness and any other demanding requests. As one of the most experienced PCB manufacturers and SMT Assemblers in China, they pride themselves to be our (the Makers) best business partners, as well as good friends in every aspect of our PCB manufacturing needs. They strive to make our R&D work easy and hassle-free.

How do they do that?

PCBWay is NOT a broker. That means that they do all manufacturing and assembly themselves, cutting out all the middlemen, and saving us money.

PCBWay’s online quoting system gives a very detailed and accurate picture of all costs upfront, including components and assembly costs. This saves a lot of time and hassle.

PCBWay gives you one-on-one customer support, that answers you in 5 minutes ( from the Website chat ), or by email within a few hours ( from your personal account manager). Issues are really resolved very quickly, not that there are many anyway, but, as we are all human, it is nice to know that when a gremlin rears its head, you have someone to talk to that will do his/her best to resolve your issue as soon as possible.

Find out more here

Assembly and Testing

This device does not need a stencil for assembly, but using one will definitely speed up things. I chose to do this build all by hand, from applying solder-paste, up to placing components.

Soldering was done on a hotplate, as usual, to reflow everything at the same time. TH components were then placed and hand-soldered.

Uploading the initial firmware, after adding the device to ESPHome was done with an external USB-to-UART converter. All further firmware changes were made via OTA.

It is important to mention here that this PCB is powered by mains voltage. I chose to use an inline fuse, BEFORE the connector on the PCB. It is also notable that the relay common is connected to the live wire, BEFORE the fuse, as the lightbulb acts as its own fuse – it blows when a fault occurs.

The Lightbulb neutral will be connected to the circuit breaker, together with the device live and neutral.

This way, the fuse only acts on the actual device, and I can use a lower-rating fuse, since I do not have to accommodate the current from the lightbulb as well…

Summary

The device works as planned, with no problems…
Below is some pictures from it in Home Assistant

ESP8266-12E in Arduino Form Factor

As a followup to my recent ESP32-S in Arduino Form Factor device, I decided to also produce a similar circuit board for the ESP8266-12E. Although some people mostly consider these as obsolete, I still find them extremely useful for small projects, and thus use quite a lot of them.

With their lower total pin count and similar low cost to the bigger ESP32 modules, these do force you to get quite creative with the available pins, as well as how and what you can interface.

What is on the PCB?

For this design, I have once again tried to keep it very lean, including the absolute bare minimum supporting components needed for correct operation.
This includes pull-up and pull-down resistors on the various strapping pins, as well as some decoupling capacitors.

I also did not include a USB-to-Serial converter circuit, as these are used only once or twice, and also consume power while not being needed all the time.
As most of my devices are uploaded OTA anyway, an external stand-alone USB-to-Serial adapter is perfect to upload the initial firmware.

Jumpers to control the onboard I2C pullup-resistors, as well as the Wake-up-from-deep-sleep function on GPIO16 were also added, in addition to the Reset and Flash push-buttons to place the device into initial programming mode.

A 3.3v LDO regulator was also added, for convenience mostly, when powering the device from a bench power supply unit. The recommended voltage for this LDO would in my opinion be 7v Dc, although the datasheet states it can be up to 15v DC… In my opinion, that stresses the component a bit much though, as most of that excessive voltage is dissipated as heat.

PCB Layout – Blank board, front and back

To try and minimise heat-related issues with the LDO regulator, I have incorporated an on-PCB heatsink for the LDO regulator, which is via-stiched together on both sides of the PCB. This type of heatsink seems to work quite well in many of my other designs, so I decided to use it here as well.

I have also made use of big copper pours on both sides of the PCB to ensure that there is a good ground plane, as well as make use of differential pairs for the routing of the UART and I2C tracks.

Schematic

PCB Design

Manufacturing

The PCB for this project has been manufactured at PCBWay.
Please consider supporting them if you would like your own copy of this PCB, or if you have any PCB of your own that you need to have manufactured.

You can get your own copy here

Some assembly pictures

Procedure to upload initial firmware

Due to the fact that this device does not have an onboard USB-to-UART (Serial) converter, it will be necessary to use an external device the first time that you upload firmware, or while you are using it on the bench if you do not want to use OTA…

The easiest way to do this, in my opinion, is the following:
1) Power the device from a bench power supply, set at 7V DC via the VIN and GND Pins, available on the bottom left and right of the device ( you can use either side, not both 🙂

2) Now connect your external USB-to-UART converter to the device, as follows:
UART Converter <-> ESP-12E Dev Board
Rx <- TxD
Tx -> RxD
Gnd — GnD

Do Not connect the power (VCC) from the USB-to-UART Converter!

Now start your Adruino IDE, or similar, and connect to the Serial monitor.
Press the reset button on the board, and watch for output in the serial monitor.

If you see output, at 115200 BPS, press end hold flash, and then press and let go of reset, while still holding the flash button.

Wait a few seconds, and then upload your sketch, remembering to manually reset the board after the upload has completed.

I would recommend that you upload the Arduino OTA sketch, from the examples, and modify it to connect to your local WiFi. That way, you will be able to upload all following sketches via your local Wifi, providing that you do not remove the OTA code from the sketch.

A RISC-V IoT Development Board

Most of us will not know about RISC-V, or have had access to a RISC-V Chip.
This will thus be truly one of the most difficult posts I have written, due to many factors…

To name a few of these:
– The learning curve is extremely steep because there is extremely limited information available on the chip
– I can not at the moment allowed to divulge any information on the chip used, as I have received a few “sneak-preview” modules, and the manufacturer, who shall also remain anonymous for now, has not released it to the public yet.
– Most of the information available on the BL-602 ( on which the chip is based) is in relation to the BL-IOT-SDK, or Apache NuttX, an RTOS for use with microcontrollers.
While the NuttX project has excellent documentation, it is written in a very technical style, and focused on very basic, very advanced or very specific things. This will hopefully be improved upon to make it more “new-end-user-that-is-learning” friendly in future.

As most of us can no doubt see, This post is quite a challenge. I will thus focus on the PCB I designed to use with the “mystery BL-602” chip, and provide a lot of links to where you can get information on Apache NuttX, as well as how to use it with the BL-602 in general.

Once the module has been officially released, I will do a followup-post, with specific documentation etc, which, although I have already got some of it in my possession, I can not release at the moment for ethical reasons.

I think it fair to tell you all this much, and , unintentionally, have to create anticipation on what and where etc… My apologies for that, but rules are rules, and secrets are meant to be kept, until told otherwise…

So, lets get started. Some links to get you started and show you where this is going…

Apache Nuttx is the RTOS that you will most likely have to use to do anything useful with the BL-602 chip, as well as other microcontrollers, notably the ESP32-S3 and some of the STM32 chips.

Bouffalo Labs are the people behind the BL-602, as well as the BL-IOT-SDK, which will also be quite useful in designing solutions around the BL-602

Run Rust on RISC-V Firmware will provide some excellent points to get started

LEE Lup Yuen seems to be the kind person who has written most of the extensive and useful documentation on NuttX and the BL-602, amongst others…

NuttX Incubator on Github is a very detailed source, also by Mr Lee Lup Yuen, that aims to get us started with the BL-602 and NuttX – This link is HIGHLY recommended!

My Prototype PCB

Carrier PCB – Disclaimer – I have edited the silkscreen to remove Chip markings- This will be released to the public at a later stage. As mentioned above, it is necessary at this moment to keep this information confidential.

I decided to design an extremely basic, bare PCB with basically just the BL-602 chip and its supporting circuitry. This will allow me to focus only on the chip, as well as provide maximum flexibility in the future by the addition of add-on shields with specific functions. with this in mind, I purposely chose a PCB footprint similar to the Arduino UNO.

It is also worth mentioning that the chip module used on this PCB IS NOT a standard BL-602, although the footprint looks similar.

At the moment, I am however pulled between being frustrated at the lack of available information and also being excited at the possibilities that are already there or will open up in the future.

Needless to say, some people will be frustrated at the “seeming lack of details in this post”. Lets all stay calm, and remember that I will post a followup, with all the details soon.

Manufacturing

Over the past eight years, PCBWay has continuously upgraded their MANUFACTURING plants and equipment to meet higher quality requirements, and now THEY also provide OEM services to build your products from ideas to mass production and access to the market.

If you would like to have PCBWAY manufacture one of your own, designs, or even this particular PCB, you need to do the following…
1) Click on this link
2) Create an account if you have not already got one of your own.
If you use the link above, you will also instantly receive a $5 USD coupon, which you can use on your first or any other order later. (Disclaimer: I will earn a small referral fee from PCBWay. This referral fee will not affect the cost of your order, nor will you pay any part thereof.)
3) Once you have gone to their website, and created an account, or login with your existing account,

4) Click on PCB Instant Quote

5) If you do not have any very special requirements for your PCB, click on Quick-order PCB

6) Click on Add Gerber File, and select your Gerber file(s) from your computer. Most of your PCB details will now be automatically selected, leaving you to only select the solder mask and silk-screen colour, as well as to remove the order number or not. You can of course fine-tune everything exactly as you want as well.

7) You can also select whether you want an SMD stencil, or have the board assembled after manufacturing. Please note that the assembly service, as well as the cost of your components, ARE NOT included in the initial quoted price. ( The quote will update depending on what options you select ).

8) When you are happy with the options that you have selected, you can click on the Save to Cart Button. From here on, you can go to the top of the screen, click on Cart, make any payment(s) or use any coupons that you have in your account.

Then just sit back and wait for your new PCB to be delivered to your door via the shipping company that you have selected during checkout.

ATMega 328P Based PWM controller Card

As part of my recent ESP-12E I2C Base Board project, I designed an ATMega 328P Based PWM controller card, that can be used as an add-on card with the existing project, or standalone as a custom Arduino Nano compatible development board.

What is on the PCB?

The PWM controller card contains standard Arduino Nano circuitry running at 16MHz, without the USB to Serial converter, as well as a 3v to 5v level converter on the I2C port ( A4 and A5 ), as well as another 12v to 5v level converter, with a build in resistor-divider circuit, used to drive a 12v blower with 3.3v PWM control circuitry.

All analog inputs are broken out to make attaching additional sensors easier.

All the other unused GPIO pins are also broken out, either directly to headers on the PCB (D6~,D7,D8,D9~), D11,D12,D12 (ISCP Header) and D3 ( Marked RPM on the Fan Header)

Most of these pins are also additionally broken out onto the 2x20p female header at the bottom of the card ( See schematic for more details)

The board is designed to be powered from 12v DC (via the VIN pins on the 2x20p header) which is internally regulated down to 5v via an LDO voltage regulator.

External 3.3v should also be supplied to the 2x20Pin header to enable the I2C level converters on the same header. I2C is not directly broken out onto the PCB in this version of the PCB.

A reset button, and power led, as well as the standard led on D13 is also provided.

Manufacturing the PCB

Over the past eight years, PCBWay has continuously upgraded their MANUFACTURING plants and equipment to meet higher quality requirements, and now THEY also provide OEM services to build your products from ideas to mass production and access to the market.

4) Click on PCB Instant Quote

5) If you do not have any very special requirements for your PCB, click on Quick-order PCB

VC-01 and VC-02 Offline Voice Module

In a recent article, I took a look at the new VC-01 and VC-02 Voice offline voice modules from AI-Thinker. I mentioned that I was working on a very simple prototype PCB to do some more tests, as well as make practical use of the module in real life.

In this very short post, I will show off the initial prototype that I came up with.
While I have to admit that it is still in an extremely basic stage, It is already definitely useful.

Part of the reason for this is that there is not a lot of information available on the VC-01 and VC-02 at this stage, as well as the fact that more exotic features like I2C and SPI are still not accessible in the current firmware. I thus had to work with what was available, as well as take into consideration what will work with the standard factory firmware as well.

The prototype carrier PCB will thus only have two optically isolated relays and their supporting circuitry. I intend to actually use the PCB in my EE LAb area to control some of the lights in the area.

The Schematic

The schematic shows the relay control circuitry, comprising of my standard optic isolator-based relay driver, as well as headers to accept the VC-01 or VC-02 offline voice module kit PCB.

Testing the PCB

The PCB was tested using the standard factory firmware, as well as my custom firmware, kindly provided by AI-Thinker. Below is a short video of that in action. Please note that the relays was not yet connected to any external devices at this stage.

Manufacturing the PCB

Over the past eight years, PCBWay has continuously upgraded their MANUFACTURING plants and equipment to meet higher quality requirements, and now THEY also provide OEM services to build your products from ideas to mass production and access to the market.

4) Click on PCB Instant Quote

5) If you do not have any very special requirements for your PCB, click on Quick-order PCB

True OFFLINE Voice Assistant

Most of us are familiar with voice assistants these days; Google Assistant, Siri and Alexa are obviously the most well-known of these. They all share a common problem though: They are online, and can thus secretly record everything you say around them, for later use by their respective owners [ The Companies that created them ]. Having a true offline voice assistant can thus seem like the holy grail for privacy and security-minded people.

Introducing VC-01/VC-02

I was recently contacted by AI-Thinker and asked if I was interested to play with a new product of theirs, an offline voice module. I immediately jumped at the opportunity, as this was something that I wanted to get my hands on for a long time, providing it works of course…

AI-Thinker’s offline voice module is available in two models, the VC-01 and the VC-02.

My Sales Representative (Kat ) sent me both models, in a kit format, complete with speaker and microphone. The kit PCB also provides a USB port with a ch340 chip, as well as two push buttons (reset and wake-up) as well as 3 built-in LEDs ( White, Orange and Blue ).

These light up with the factory firmware, depending on what commands are issued to the device…

Let us take a look at how the factory firmware works; Thank you to Kat from Ai-Thinker for uploading the video, and sending the link to me 🙂

As we can see in the video above, the module seems to work very well… The question now arises if it can be customised to do what we want it to…

Custom Firmware – Do-able, but with a few caveats

Information in English on this module is very sparse. This is due to it being very new, and with AI-Thinker focusing most of their efforts for this module on the Chinese market for the time being. Which makes sense in one way, but also doesn’t in another.

After spending quite a bit of time trying to get information, my Sales Rep eventually gave me access to an online configuration utility, now be warned:
This is not for the faint of heart. The entire interface is in Chinese ( They are working on an English version, with time-to-completion between one (1) to four(4) weeks from starting the project. I can however not give any accurate dates at this stage, but was told that this development is underway).

Being no stranger to different languages, I thought to use google translate to translate the website. No, that didn’t work. Google refuses or the Chinese Website doesn’t allow it to? No answer as of yet. Any readers who do know any reasons for this, please comment below.

I was sort of successful in manually copy pasting line by line into google translate and got some translation back, but it was not very useful.

My next point to try was asking AI-Thinker to generate some firmware with the web tool. They gladly did that, and that works great. It is however not feasible in the long term to go that route every time.

This was possible because the AI-Thinker engineers, using the firmware development software, currently only available in Chinese, can set custom wake words and train voice commands with a 95% accuracy rate, before generating firmware and flashing it onto the respective module.

Write your own, someone will obviously say, and that was my next attempt. There is an API, and source code on GitHub, as well as Gitee ( The Chinese version of GitHub) The two sources are however not synced, and I was still not successful in getting anything useful from Gitee, once again due to a language issue, as well as the fact that some of the sources depend on 32bit dependencies for Ubuntu, whereas I am running a 64bit version… I did try it though, and can not report any success on that venture at all.

Once again, I will advice us all to wait for AI-Thinker to release an English version of the SDK and API for us all to use, which I am sure they will do at some stage in the near future.

See the video below of my custom firmware, once again demonstrated by Kat from AI-Thinker

Custom Firmware – Test 01

As we can see, it once again performs well, with a few issues, but quite acceptable…

Hardware access to the real world

As we have just seen in the video, there is also hardware access via pins, to the real world. There are however a few issues there as well…

Hardware pins are limited.
I2C and SPI, although advertised, are apparently not yet supported in any of the current firmware – Someone with information, please comment…

While there are 2 I2C interfaces, they can not be used at the same time
Information on the module

PCB Prototype – Of my own design

As a proof of concept, I have decided to design a quick prototype with relays to use as a more detailed test. I will update information on that soon…

My Conclusion

I definitely see potential here. This is a product which can be quite useful in the future, providing that the following is done:

Proper detailed documentation is provided in English as well as Chinese
API and SDK access is made available in English as well as Chinese
Firmware be updated to make all features available

Having said all of that, I do understand that development, and especially R&D do take a lot of time. Translating documents accurately does too.

I want to congratulate AI-Thinker on producing a very well-made unit, that will definitely bring the dream of a totally offline voice assistant a little bit closer to being a reality.

Voice recognition with my bastard South-African/British English Accent, heavily influenced by Afrikaans, went extremely well, even with the factory firmware.
I do thus not think anybody that can speak passable English will have a problem using the unit.

ESP-12E I2C Base Card

As a follow-up on the ESP-12E Card, today we will look at the prototype base card that this was designed to slot into – The ESP-12E I2c Base Card.

Initial Features ( To be expanded in future versions )

4 x 40Pin Expansion slots, with access to 12v, 3.3v and Gnd on each slot.
2 x “IRQ” pins per slot ( serviced by a single PCF8574 )
I2C bus access on each slot (3.3v )
UART Header
Reset and Flash Header
GPIO Header ( Direct access to the ESP-12E GPIO Pins )
Analog Input Header (a Single input – A0, as per ESP-12E limitation)
Buck Converter Power Supply Module, capable of up to 2A of current

The Schematic

The PCB – some pictures

Manufacturing the PCB

Over the past eight years, PCBWay has continuously upgraded their MANUFACTURING plants and equipment to meet higher quality requirements, and now THEY also provide OEM services to build your products from ideas to mass production and access to the market.

4) Click on PCB Instant Quote

5) If you do not have any very special requirements for your PCB, click on Quick-order PCB

ESP-12E Card

A few months ago, I started working on an MCU Card design, which borrows from the idea of a standard desktop PC, in which there are a main-board, MCU and expansion slots, to add and remove peripherals as needed quickly.

The ESP-12E Card is a continuation of that project, with the ultimate goal to have a universal “main-board” that can accept various MCUs and standardised “expansion modules” that perform a specific task.

The PCB

The ESP-12E Card contains the bare minimum components to allow the chip to function. There are no power regulators or USB-to-TTL converters onboard. Code is flashed via an external USB-to-TTL converter, with Flash and Reset buttons on the actual PCB, or available in the 2×20 Pin female header at the bottom of the card.

Most of the GPIO is also broken out to the 2×20 pin header, with the exception of the 6 GPIO that is usually connected to the internal Flash on the ESP-12E module.

I have made provision for enough power and ground pins on the header as well.

As far as GPIO is concerned, They have been grouped together by function, as much as possible at least, to make interfacing with the base-board as easy as possible.

The Schematic

The schematic is not complicated. It is a standard ESP-8266 configuration, with all non-essential components removed.

The “base-board” ( a sneak preview )

In a future article, I will tell you more about this ( for the time being limited to I2C ) base card. [ a quick explanation: When I mean limited to I2C, it relates to the fact that at the moment, the base card, ( a prototype ) can only communicate back to the MCU via I2C protocol from each of the expansion slots, as well as via two dedicated IRQ lines from each slot ]Power is supplied via a small SMPS module.

Manufacturing the PCB

Over the past eight years, PCBWay has continuously upgraded their MANUFACTURING plants and equipment to meet higher quality requirements, and now THEY also provide OEM services to build your products from ideas to mass production and access to the market.

4) Click on PCB Instant Quote

5) If you do not have any very special requirements for your PCB, click on Quick-order PCB

Easy to use CAN-BUS Module with Relay, LiPo Battery Backup

Can Relay Module running on battery power

CAN-Bus allows us to add a lot of devices to a single bus (theoretically up to 127, with a practical limit of about 110). It was logical to decide to use CAN-BUS for communication between my LoRa-CAN Module and remote nodes in my ongoing farm telemetry system. In a previous project, I introduced the LoRa-CAN Gateway, which will be used to send/receive messages from the master control unit, the SX127x-RA-02-Module.

Today, I will focus on the design of the node device, an Arduino compatible CAN Relay Module PCB, with a built-in, CAN Controller and Transceiver ( MCP2515 and TJA1050 ), and the option to be powered from a LiPo battery (18650 or Single 3.7v Lipo cell), with charging provided by an MH-CD42 Module, similar to that used in the SX128x project mentioned above. The Module can also be powered directly from up to 12v DC by placing Jumper H2 in the V-REG position…

As mentioned in a previous project, the MH-CD42 module can provide up to 2A of current to charge a battery and provide 5V DC on a direct bypass circuit to power the rest of the circuit while the battery is being charged. This feature makes it ideal for my intended use, as I would only be needing battery power at night when the off-grid solar powered inverter is not actively charging the main batteries, and providing 220v AC.

The CAN Relay Module PCB was designed to be as compact as possible, with a total footprint of the standard Arduino UNO. As space was at a premium, and to ensure that there are the absolute minimum additional components that will consume power when operating from the battery, I have not included any USB-to-Serial converters onboard. Firmware can be uploaded with an AVRASp, USBASP, Arduino as ISP or even an external USB-to-Serial converter ( providing that you load a bootloader into the Atmega Chip).

All of the unused GPIO pins on the ATMEGA chip is broken out into headers, with the exception of D10 ( which is used as CE/SS on the MCP2515 CAN controller), D9 which is connected to the Interrupt from the MCP2515, and D4, which is used to control the onboard Relay.

Can Relay Module with LiPo cell and MH-CD42 Module

The MH-CD42 Module, and LiPo or 18650 Battery are completely optional, The device can function without these, by moving the H2 jumper to the VREG position as already mentioned above. This will divert the DC Voltage(Up to 12v) from the DC input adapter to the build-in 5v LDO voltage regulator to power the device.

If you place the H2 Jumper in the VBAT position, you need to install the MH-CD42 module to provide power to the rest of the PCB, as well as keep the LiPo battery or 18650 Cell charged…

Please NOTE:

When the MH-CD42 module is in use, the total DC input voltage through the DC input adapter SHOULD NOT exceed 5.5v DC! This is a limitation in the operating parameters of the MH-CD42 module. Not paying attention to this will result in damage to the MH-CD42 Module.

You could also power the module with REGULATED 5v DC, directly from any 5v header pin. Please note that in this case,

1) The battery won’t be charged.

2) The LDO regulator will not be in operation.

The Microcontroller

The CAN Relay Module can use any of the ATMEGA8a/88/168/328 AVR microcontrollers, as the pinout is identical. I believe this is an advantage, especially with the current chip prices, where my last quote for an ATMEGA328P-AU was 69$USD!!!! This is in comparison to the 4 to 5 USD each for an ATMEGA8a or ATMEGA168 ( We must also remember though that the 328p is very well known, and thus have higher demand. The 8a/88 or 168 are less well known, have much less memory and flash area, and will thus be cheaper. A word of action though, I had strange issues with I2C on the Atmega8a with Mini core, to such an extent that I2C does not work at all?

If you plan to use I2C on this board, install a 328p right from the start, and save yourself a lot of headaches!

This is the Relay driver circuit. As you can see, it is optically isolated, and active LOW. This means that you have to pull D4 LOW to energise the relay. Also note that, although the relay is optically isolated from the microcontroller, the coil is NOT galvanically ISOLATED. The load, which is magnetically switched, will be truly galvanically isolated, providing of course that you don’t do something silly like using a common ground to the PCB as a common on the relay…

This is the Processor and Power-supply schematic. The circuit is basically a standard Arduino Nano, with modifications for the CAN Controller on the next schematic page. Note that the MH-CD42 is not shown on the schematic. The VBAT net connects directly to the VIN pin on the unit, with the BAT net connecting to the positive of the battery. VOUt-5v from the module goes directly to the 5v net. All grounds are commoned.

This is the CAN Controller and Transceiver circuitry. The MCP2515 connects directly to the SPI bus on the microcontroller via D13, D12 and D11, with D10 as CE/SS and D9 as Interrupt or IRQ. It is important to note that although the MCP2515 is a 3v capable device, the TJA1050 Can transceiver is 5v only. This prevents us from running the PCB at 3v unless, of course, we change the TJA1050 out for a 3v capable device…

CODE

The board has been extensively tested with Cory J Fowler’s mcp_can Arduino Library. It works very well indeed.

As I am currently working on the final integration of the two modules, I am not yet ready to publish my final code, showing the operation between the CAN-Bus and LoRa-to-CAN Gateway device in this post. Once I am happy that all issues are definitively sorted out, I will publish my code.

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CAN-to-LoRa gateway using RA-02, MCP2515 and ATMEGA328P

ATMEGA328P Module with integrated LoRa and CAN-BUS

INTRODUCTION

In my quest to perfect my LoRa telemetry system, I have gone through quite a few prototypes by this time. This post will focus on the next node design. Due to the fact that the area where I will deploy the system is quite large, but with roughly square boundary fence-lines, I decided to try and reduce the number of LoRa Radio nodes needed to cover the entire area. This opened up the opportunity to utilise CAN-BUS to attach sensor-only nodes to a Radio node and have them report status on exception as well as on requests from the radio node.

The device will thus function as a LoRa-to-CAN-BUS Gateway, with some local automation to control the transmission of data to the master station. This concept can also be adapted for use in other areas, such as home -automation, or an industrial setting.

At the heart of the device, I have stuck with the versatile ATMEGA328P, which, current chip shortages excluded, and current high prices excluded, are a very inexpensive chip, with lots of well-tested libraries, and a relatively low learning curve, largely due to its very wide use in the Arduino ecosystem.

The LoRa component is handled by the RA-02 or even RA-01H module, from AI-Tinker (not sponsored). This device, as we have seen in the previous prototypes, requires the use of logic level converters, due to the fact that it only accepts 3.3v logic levels. While I could get rid of those if I powered the ATMEGA328P from 3.3v, it would give rise to two problems, of which one will still force the use of level converters…

I chose to run the ATMEGA328P at 16Mhz, which basically forces me to use 5v to power the chip. The second reason is not so obvious unless you read a few datasheets very thoroughly…

The CAN-Bus component is handled by the MCP2515 Standalone SPI-to-CAN Controller, as well as the TJA1050 CAN Bus transceiver.

This is where things get interesting… The MCP2515 can operate on 3.3v, but the TJA1050 is a 5v only device. I could thus in theory use logic level converters only between the MCP2515 and the TJA1050, while running the rest of the circuit on 3.3v…

Given that I would rather run the ATMEGA328P on 16Mhz, as well as the fact that my LoRa Radio Module circuit, with its logic level converter circuitry, works extremely well, I decided not to change that, and keep the CAN Bus running at 5v all the way through, as I would still have to use a 5v regulator on the PCB anyway just for that purpose.

IO connections for LoRa and CAN BUS modules

You can order this PCB directly from PCBWay, by clicking here

Both of the two integrated components ( Lora and CAN ) are SPI devices. This means that they share common SCK, MISO and MOSI lines ( provided on the ATMEGA328P by pins D13, D12 and D11 respectively. The individual SPI device is then further selected for operation by the use of a CE pin, one unique pin per device, which is pulled low by the MCU to indicate to the device that it should pay attention to the data being transmitted on the SPI bus…

Both LoRa and CAN makes use of other pins as well, LoRa needs a Reset pin, connected to D9, a CS/CE Pin on D10 as well as a hardware interrupt pin, connected to D2. ( Note that this is for use with Sandeep Mistry’s LoRa Library. The Radiolib library would require an additional pin, usually connected to DIO1 on the LoRa module. The device does not provide access to those pins in its current layout, so you can only use it with the Sandeep Mistry library, for now at least… )

The CAN module uses a CE/CS pin at D4, with an IRQ pin on D6, which, although not a hardware interrupt pin, does have PCINT functionality.

Pins D10, D9 and D2 are not broken out for user access. although I decided to give access to D4 and D6, as well as the SPI bus, D11, D12, D13, to allow interfacing with logic analysers, or adding other SPI devices to the bus…

This brings us to a very interesting point… Does the two SPI devices actually play nice together? and what do I mean by “playing nice together”?

To answer that question, we are forced to first look at a bit of theory, as well as understand the fundamental differences between SPI and I2C…

The Difference between SPI and I2C

Most of us will be quite familiar with I2C, as it is a very common protocol used to connect sensors to a microcontroller. It consists of only two IO lines, SDA for data, and SCL for the clock. Each device on the bus has its own built-in address, like in the case of a PCF8574 IO expander, this address can be selectable between 0x20h and 0x27h. All of the devices share these common data lines, and will only respond when specifically addressed by the master controller… Unless you accidentally put two devices with the same address on the same bus, (if that would even work), there is no way that the wrong device would respond to any request for data…

SPI on the other hand, operates on a completely different principle, making it quite a few times faster than I2c, with data being simultaneously sent and received by the active device… SPI is also known as a four-wire protocol. Each device has a minimum of 4 data lines, namely SCK ( clock), MOSI ( for data transmitted FROM the Master TO the slave device ), MISO ( for data transmitted TO the master FROM the slave device) and a CE or CS ( Chip select ) pin.

SCK, MISO and MOSI are COMMON to all devices, meaning it is shared between all of them. CE/CS is a unique pin for EACH device, meaning that if you had four SPI devices on a bus, you would have to have four individual CE/CS pins!

A device will, or rather should only respond to data on the SPI-BUS IF the master pulls its respective CE/CS pin LOW. It should now very quickly become clear to you that this can become a very very complex mess, very quickly.

Let us take a very good example. the ST7789 SPI display module, has a cheap version, commonly sold on Ali-express, as we ll as other online stores. This particular module, I assume in a bid to make it easier to use, has the CE/CS pin internally pulled down to ground by default… So what about that, you may ask? What is wrong with that, as it saves you an IO pin?

It is in fact very wrong, a fact that you will very quickly discover if you ever tried using one of those displays on an SPI bus together with other SPI devices… Nothing will work, or only the display will work ( if you are lucky)

But why?

Pulling CE/CS LOW, signals to the chip that it should respond to instructions on the common SCK, MISO and MOSI lines. having the pin internally pulled LOW, thus forces that chip to always respond, even when it should not. Thus contaminating the entire SPI-BUS with garbage…

The answer to the question

After that very long-winded explanation, which is still extremely basic, it is time that we get back to our original question:

Does the Sx127x ( RA-02 ) Module and the MCP2515 Can Controller play nice on the same bus? The answer is not straightforward, as it comes down to which libraries you use…

Remember that the library must pull down the CE/CS pin of the device that it wants to communicate with. Some libraries wrongly assume that they are the only ones in use, and ignores the simple fact, that they should release the CE/CS pin AFTER EVERY transaction, to free up the bus for other devices to use it as well…

After extensive testing, I can however say that Sandeep Mistry’s LoRa Library, as well as the mcp_can library, does indeed play nice together. These two libraries do not keep the individual CE/CS pins pulled LOW, and allows the spi bus to be shared.

This is not the case with the ST7789 Module discussed above, where the hardware actually pulls the pin ow the entire time…

Taking a closer look at the PCB

Let us take a closer look at the PCB. The Ra-02 Module ( LoRa ) dominates most of the left-hand side of the PCB, with the ATMEGA328P on its right. The RA-02 is surrounded by the level converters, using the BSS138 N-Channel Mosfet, and 10k resistors (Q1 to Q6, R1, R2, R3, R4, R5, R6, R8, R9, R10, R11, R12, R13)

C1 and C2 are bypass capacitors for the Ra-02 module

In the bottom left corner, we have a hardware reset button, to reset the ATMEGA328P, with a yellow jumper (H1) next to it. This jumper controls the 120ohm ballast resistor (R17) for the CAN bus. Removing the jumper will remove the ballast. Directly below that is the CAN connecter, marked as U5, with CH as CAN-H, and CL as CAN-L ports.

U3 and U4, together with R18, R19, X2, C16, C17 make up the CAN components on the PCB. Decoupling is provided by C6, C7, C8 as well as C9 and C12 ( Includes the ATMEGA328P’s decoupling as well )

An ICSP programming header is provided above U1 ( ATMEGA328P) for use with USPASP, AVRASP or Arduino as ISP and similar.

No USB to serial converter is provided on the board, Serial upload is possible is loaded with an Arduino bootloader for the Arduino NANO ( to make use of all the analog inputs). RxD, TxD and DTR pins are broken out on opposite sides of the PCB, as well as access to 3.3v, 5v and GND pins.

A DC power socket is provided. it can accept up to 12v DC, although I would recommend not to go over 7.2 volts, to not stress the LDO regulators, at the back of the PCB ( LDO1, and LDO2) too much.