PCBDesign - Maker and IOT Ideas

Get Started with the ATMegaTiny202

As I have hinted in my recent two posts about UPDI programmers, I am currently looking for a solution to replace the ATMEGA328P chip used in standard Arduino devices, like the UNO and NANO.

The global chip shortage seems to be still hitting hard, with these devices (Arduino UNO, NANO), and even bare chips being quite hard to get hold of, and when you do, they are quite more expensive than they used to be.

This sent me on a new journey, to find a new chip, that is easy to use, inexpensive, and easy to get hold of. I have found 3 of these chips, starting today with the ATMEGATiny202,

The ATtiny202 is a microcontroller using the 8-bit AVR® processor with a hardware multiplier, running up to 20 MHz and 2 KB Flash, 128B SRAM, and 64 bytes of EEPROM in an 8-pin package. The series uses the latest technologies from Microchip with a flexible and low-power architecture, including Event System and SleepWalking, accurate analog features and advanced peripherals.

With only 8 pins, of which we can practically use only 5 ( 6 if you have an HV UPDI programmer ). This makes it a desirable solution for small projects, with its current price of about 0.59 USD per chip ( SOIC8 PACKAGE, Element14 ) , not breaking the bank either. Not needing an external oscillator, and requiring only a single 100nf bypass capacitor, (not counting the UPDI resistor) it can indeed be a very very cheap way to get a project done… Providing of course that you don’t need a lot of Program memory or RAM, and are not trying to do too many super fancy or complicated things.

ATMegaTiny202 Minimal Breakout, on Breadboard with MakerIoT2020 Multipurpose Uart/UPDI Programmer

The wide operating voltage of 1.8v right up to 5.5v also makes it quite flexible.

My initial prototype

Getting started with a new chip is also a bit of an issue, as there are many new things to learn, recommended supporting components, and also firmware and cores that need to be installed. I have decided to build a quick breadboard-capable PCB, with all 8 pins broken out in a single row, feel free to change the straight header pins to a 90-degree version at your convenience, it takes up even less space that way.

The PCB contains only the bare minimum required components for the chip to function, but I also added onboard I2C pullup resistors, with a jumper to select them. ( Most I2C modules usually have these already, but as I build most of my own breakouts myself, I decided to include these).

A single LED brightens things up a bit, connected to pin PA3, making it possible to run a blink sketch…

The rest of the components include a 100nf bypass capacitor and the very important 470ohm UPDI resistor.

ATTiny202 Breakout-Blank PCB-Top — PCB Top view, unpopulated

Programming the board

I use the Arduino IDE quite a lot, and also assume that most makers and hobbyists out there will do the same. Luckily we have access to a special Arduino core, the megaTinyCore, that provides us with all we need to program this tiny little chip, provided of course that you have a UPDI programmer.

See the link above for installation instructions, as well as detailed documentation. Replicating all of that here will be an unnecessary task, as the author of the core, SpenceKonde, has already done an excellent job.

One very important thing to note on this board is that there is NO RESET PIN.
You have to manually cycle power to it, but, I have found that initiating a UPDI upload to a running chip works every time, and makes it unnecessary…

The reason for the lack of a reset pin lies in the fact that the reset is shared with the UPDI pin, and enabling it, will rob you of the UPDI functionality UNLESS you have an HV UPDI programmer, which at this time seems to be hard to find/expensive item ( Hope to build my own soon). Once again, see the above link to the core documentation for the full information on the reset pin issue…

I can not stress enough how important it is to sit down and READ the core documentation, with attention, before doing anything with this chip and core. you will learn a lot, about the chip, new features, possible problems, and how to avoid them, and also some customised GPIO functions etc…

Schematic

Schematic_ATTiny202-DEV_2023-02-22 Download

Manufacturing

The PCB is a double-layer PCB, with the signal traces on the top layer, power traces, and the ground-plane, on the bottom layer. the Dimensions are 26.035mm x 18.669m. All SMD components are 0805. This board does not need a stencil for assembly and can be hand or hot-air soldered in a few minutes with no problems.

As many of my existing readers will know by now, 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

Picture Gallery

ATTiny202 Minimal Breakout — ATTiny202 Minimal breakout. All you need to get started, just add a UPDI programmer, Arduino IDE, and the MegaTinyCore…

ATTiny202 Minimal breakout. All you need to get started, just add a UPDI programmer, Arduino IDE, and the MegaTinyCore…

555 based Latching Switch

The humble 555 timer IC has been around for a very long time. It can be configured to do a lot of timer based functions, the most common know being to flash LED’s at a given frequency.

A slightly more unknown function of this versatile chip is the capability to be configured as a latching switch, -meaning a press on press off switch-.

In this short two part series, I will show two such latching switch modules that I have designed around the 555 timer. In the first part, we will look as a single latching switch, with an attached relay output to switch higher current and voltage loads safely.

The PCB

With only 11 components ( excluding the relay and connectors or course) this is an extremely easy and cheap circuit to build. It can also quite easily be built on a breadboard, or strip board, if you do not want to use a custom PCB.

Operation of the Circuit

The operation of this circuit is quite easy. The PCB is powered by a 5v supply, in this case, but the 555 can allow for a supply voltage of up to 15v DC ( Please note that the Relay needs to be capable of accepting the input voltage without damaging its coil… you would thus have to select a suitable model)

When you press and release the push button, pin 3 of the 555 will go high, lighting the indicator LED, as well as pulling the gate of the BSS138 Mosfet High, allowing current to flow through the relay coil, thus energising the contacts.

The relay will stay energised until you press and release the button again, or power is removed from the circuit.

Possible uses

This type of circuit has many uses, like switching a light on and off with a single press. It is obviously cheaper and easier to just use a toggle switch, but it is also interesting to explore the possibilities of a discrete component solution, without a microprocessor, to achieve a result similar to that of a toggle or rocker switch.

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.

More Pictures

Carrier board for SEEEDuino XIAO

These days, Makers have access to quite a few different microprocessors for use in their projects. Most of them can be found on development boards of some sort, but not all are in a convenient size. The reason for this is that most of these development boards were designed with a breadboard in mind, and then after your prototype is done, you are required to design a PCB and place the specific processor and its supporting components onto this custom PCB…

Many makers choose to skip this step, either choosing to keep the project on the breadboard, or place the entire development module onto a piece of stripboard or similar, and then place their supporting components and sensors around that.

This is where the SEEED XIAO is different. It comes in a thumb-nail-sized package and can be used on the breadboard or directly placed onto a PCB via either pin headers or if you want access to all of its features, SMD pads.

In this build, I decided to design a generic carrier board, that will accept most of the XIAO RP2040 or the XIAO SAMD21

I have also included a small prototype area on the PCB, so that Makers can easily transfer their existing XIAO projects onto a semi-custom PCB, without having to design their own.

I have also addressed a problem area, especially with the XIAO SAMD21, it has no onboard reset button, only two tiny pads, by including a reset button for ease of use.

The PCB is in Arduino Uno form factor, and also provides headers to power it from an external 5v DC supply. Please note that the prototyping area has a 3.3v power rail, – due to the fact that all of the XIAO GPIO are limited to 3.3v anyway -. This power rail is powered directly from the XIAO 3.3v output, and the current is limited as per the specifications of the XIAO module that you are using.

Hardware Specifications – SEEEDuino XIAO

Hardware specifications and comparison

Processor	ESP32-C3 32-bit RISC-V @160MHz	SAMD21 M0+@48MHz	RP2040 Dual-core M0+@133Mhz	nRF52840 M4F@64MHz	nRF52840 M4F@64MHz
Wireless Connectivity	WiFi and Bluetooth 5 (LE)	N/A	N/A	Bluetooth 5.0/BLE/NFC	Bluetooth 5.0/BLE/NFC
Memory	400KB SRAM, 4MB onboard Flash	32KB SRAM 256KB FLASH	264KB SRAM 2MB onboard Flash	256KB RAM, 1MB Flash 2MB onboard Flash	256KB RAM,1MB Flash 2MB onboard Flash
Built-in Sensors	N/A	N/A	N/A	N/A	6 DOF IMU (LSM6DS3TR-C), PDM Microphone
Interfaces	I2C/UART/SPI/I2S	I2C/UART/SPI	I2C/UART/SPI	I2C/UART/SPI	I2C/UART/SPI
PWM/Analog Pins	11/4	11/11	11/4	11/6	11/6
Onboard Buttons	Reset/ Boot Button	N/A	Reset/ Boot Button	Reset Button	Reset Button
Onboard LEDs	Charge LED	N/A	Full-color RGB/ 3-in-one LED	3-in-one LED/ Charge LED	3-in-one LED/ Charge LED
Battery Charge Chip	Built-in	N/A	N/A	BQ25101	BQ25101
Programming Languages	Arduino	Arduino/ CircuitPython	Arduino/ MicroPython/ CircuitPython	Arduino/ MicroPython/ CircuitPython	Arduino/ MicroPython/ CircuitPython

The PCB

Manufacturing

More Pictures

Useful ESP12E-DEV Prototype Shield

In answer to quite a few requests for a prototype shield, similar to my ESP32-S Dev Prototype shield, but for use with the ESP-12E DEV board, I have decided to do a quick design, and make it available publicly

This is the MakerIOT2020 ESP12E-DEV Prototype Shield. It is similar in purpose to the above-mentioned ESP32-S Dev Prototype shield, but I have also added some additional cosmetic changes to make it a little easier to use as well.

With many of my prototype designs, I tend to sometimes leave out something, as I usually use it for my own purposes only, but with this design, as many people specifically asked for it, I took a bit more care, as it is no longer just a prototype, right?

What has changed?

The most obvious is the increased prototyping area. The initial ESP32-S version had a 60-hole breadboard-style prototyping area. The new design has 128 prototype holes.

There is also a dedicated power input header, something that I somehow left out on the ESP32-S version… The Flash and Reset push-buttons were also moved inline, and to the bottom of the shield, making it more comfortable to use.

The design retains the plated through-hole design on the prototype area with connecting tracks on both sides of the PCB to allow for a bit more current.

The big ground plane on both sides of the PCB has also been retained.

PCB Design and Schematic

The prototype shield is for all purposes a breadboard. I did thus not bother with a formal schematic. I believe that it is easy enough to understand the connections by just looking at the two images above.

Manufacturing

Some More Pictures of the PCB

I2C IO Card for ESP-12E I2C Base Card

The I2C IO Card for ESP-12E I2C Base Card is another expander card for the ESP-12E I2C Base Card Project. This PCB is an address-selectable I2C module with two relays and six (6) GPIO pins, all driven from a single PCF8574 running at 3v. The relays are optically isolated, and generous mains isolation cutouts were provided to reduce the possibility of mains voltage tracking. A jumper to enable/disable the i2c pullup-resistors is also provided on the PCB.

The relays are powered from a single LDO regulator, accepting 12v DC from the 2x20pin female header on the bottom of the card. 3.3v and ground should also be applied to the card at the 2x20pin header.

It is worth mentioning that this circuit does not contain level converting circuitry and that the i2c bus thus runs at 3.3v to be compatible with ESP chips.

It is possible to use the card with other processors if the appropriate level converters are used on the i2c bus.

The Schematic

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.

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.

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

iPCB-DFM – Intelligent PCB DFM

(Design for Manufacturability) Gerber Software Analyser

Free to Use for all PCBpartner.com Users

PCBPartner.com recently decided to release their own DFM software, which I believe they developed in-house and use themselves every day, to their customers, in order to enable their customers to design better PCBs and increase the overall quality and service satisfaction.

In this article, I will give the software a quick look and feel, and show you some of its features, while at the same time admitting upfront, that it is quite complex, and that I am also not quite well acquainted with it myself, having only a few days to play with it up to now.

What is DFM?

DFM (Design for manufacturability) analysis of incoming Gerber files is a standard and important process in any PCB factory. iPCB-DFM’s purpose is to perform this process automatically to find potential production issues with your PCB design, saving time and effort for you the PCB designer, and the PCB manufacturing engineers who are going to produce your PCB. Based on 25 years of PCB manufacturing experience, we have a massive collection of PCB DFM rules built into this software, allowing it to analyze up to 24 kinds of specifications.

It also has powerful features such as quick panalization, PCB simulation and direct Gerber editing, and can even help you count how many SMD pads are in your design!

Why do you need iPCB-DFM?

If you’re an electronic engineer, you don’t want to send your PCB Gerber files for manufacturing without checking that your design and file formats match your factory’s production capability; If you are a purchasing manager without much knowledge of PCB manufacturing processes, this tool can help you better understand the specifics of the PCBs you are ordering, making it much easier to communicate with your PCB suppliers.

What Features does this DFM have?

Gerber file view supports Gerber274x, Excellon, ODB++ and IPC-2581 formats
-Measuring
-Layer management
-Auto recognize layers (silkscreen, solder mask, copper, solder paste, inner layers)

-PCB simulation:
generate a simulated preview of your PCB, updated in real-time by different colour settings and surface finishes, and supporting high-resolution PNG output format.

DFM Functions

1 Layer
2 Dimension
3 Minimum trace space
4 Minimum trace width
5 Hole diameter
6 Drill slot
7 Through-hole annular ring
8 Hole distance
9 Hole to trace
10 Copper to edge
11 Special holes
12 SMD size
13 Via in pads
14 Test Point
15 Component solder pads number
16 Via density
17 Surface finish area (%)
18 Routing length of travel
19 Grid wiring
20 Solder mask
21 Fiducial Point
22 SMD pad size
23 SMD pad space
24 BGAs

Gerber Edit

1 Add elements
2 Delete elements
3 Move elements
4 Copy elements
5 Adjust circuit angle
6 Rotate elements
7 Edit trace
8 Mirror
9 Positive and negative switch
10 Break trace
11 Shape edit
12 Single, rectangular marquee, polygon selection

Panelization
Quick panelization
– set a panelization style, tooling bar width and board space,
one click to generate a panalized board in seconds in Gerber format.
Advanced panelization – allows you to adjust tooling hole, v-cut, fiducial mark, solder mask for fiducial mark, drill holes on tooling bar, etc.

What does it need to run?

For the foreseeable time forward, the software only runs on Microsoft Windows. It apparently supports from Windows XP right up to Windows 11, but I only had success on Windows 10, ( I don’t have Win 11).

This was also done in a VM running in Oracle Virtualbox on an Ubuntu 22.04 LTS host. (My main operating system)
Specifications for the VM were 4Gb RAM and a 50Gb Hard Disk. I have also tested it with 8Gb, but it did not make any real difference to the performance.
(This is most definitely NOT related to the DFM software, but more likely to be attributed to a certain heavy resource-consuming operating system (Win 10 – which as most of us know by now, is super slow whatever you give it to run on)

Installation

Installation is straightforward and quite easy, as we can expect from any Windows software these days

Getting Started

The software starts up pretty quickly, but the gets a bit of a slowdown with a login prompt tying back to PCBPartner, where you have to enter your login credentials. This can take a bit of time to actually appear.

I am hopeful that this process will in time be streamlined as I believe that the number of users on the system will grow quite fast…

Let us look at some pictures of the UI and Menu Systems

The software also comes with a very detailed Helpfile in .pdf format

help-1 Download

My thoughts on all of this

This is an extremely complex piece of software. It is also extremely powerful, and can thus be very very useful to all of us. The learning curve is extremely steep, but I do believe that it will be possible to learn and use it effectively.

As a Linux user, I would also like to see a Linux version, or at least an in-browser version, similar to a well-known EDA software package. The days that software should be confined to one operating system should be behind us ( at least in my personal view, I find it very frustrating that most other commercial CAD, CAM and EDA packages are actively forcing us to stay with one of the slowest operating systems available )

I also want to thank PCBPartner for giving me the opportunity to review and take this for a test drive. I would only have wanted to be more adept at actually getting value out of a great piece of software, but I believe that I will definitely get better at it over time.

Robotic Toy Car – Part 6

Today we will look at the remote control unit for the Robotic Toy Car – Part 6.
The project is close to being completed, and as such, there are quite a lot of final things that need to be taken care of.

One of these will definitely be the final coding, which I will release in the final part of the project, so with that in mind, let us take a look at the remote control unit.

Remote Control Unit, designed to be used with ESP-Now

I have decided to do something completely different from standard remote control units, being that I will use ESP-Now, a protocol developed by Espressif.
ESP-Now runs on the Wifi hardware of the ESP8266 or ESP32 and is basically a peer-to-peer protocol, that does not require Wifi but can co-exist with it on the same device. Outdoors, ESP-Now has a range of about 100m, which should work very well for my intended use.

The Remote control, as designed, will have 4 dedicated buttons: forward, reverse, left and right, divided into two groups to make two-handed control easier, similar to a standard game controller. No input on either of the two groups will result in stopping the vehicle, in the case of forwards and backwards, and centring the steering, in the case of the left-right axis.

a 3D Rendered Image of the PCB, motion axis on SW1 and SW2, steering axis on SW3 and SW4

As I always try to make my designs somewhat reusable for other purposes, I have also broken out most of the unused GPIO pins to header pins, with also adding a jumper on GPIO16 to make deep-sleep wakeup mode possible., You can also re-use the switch pins for other purposes, just remember to first remove the 10k pull-up resistors at R14, R15, R16, and R17…

SW4 -> R16 , SW4 = GPIO4
SW3 -> R17 , SW3 = GPIO5
SW2 -> R15 , SW2 = GPIO13
SW1 -> R14 , SW1 = GPIO12

GPIO16 can be reused as well, just remove the jumper, but remember that it is pulled up through a LED and a 470ohm resistor…

There is no USB-to-serial converter onboard, I have been having quite a lot of headaches with them over the last few months, with almost all CH340G chips that I have purchased, being fake, or dead-on arrivals that don’t work… Sending them back to the suppliers, unfortunately, results in unpleasantries, because even placing them in verified working circuits, still proves them to be not working… This is however not an issue, as it is quite easy to upload the board with an external adapter.

The Schematic

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.

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 $5USD 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

Robotic Toy Car – Part 5

In this almost post we look at the power distribution PCB for the almost completed Robotic Toy Car. I had many interesting issues to solve here, especially since I did not design my own Lipo battery charger circuit, but used a very useful little commercially available unit instead, the MH-CD42

Based on a relatively difficult chip to get information on, the module is basically an integrated Lipo charge/discharge module, with a built-in boost converter that provides 5v at a maximum of 2A current. What makes it special is the ability to simultaneously provide current and voltage, as well as charge the attached LiPo cell at the same time, when connected to an external charger.

It does, however, in my view at least, also have a few serious flaws, the most irritating of these being that it will completely discharge the attached LiPo cell even when completely switched off…

I have thus tried to stop this issue from occurring by adding a switch in line with the Lipo Cell, a quite obvious solution, but it should not have been needed if the chip functioned as intended… ( As far as I can gather, the module was originally designed to be used in USB power banks. This makes the flaw even more serious, as a self-discharging power bank really defeats the purpose)

Enough of that though, when it does work, it works great. just remember that you can not apply more than 5.5v DC to the charging input of the module.

The completed Power Distribution and charging module

The Schematic

There is actually not a lot going on here, as everything is already on the supplied module. I have just added a charging port, additional power headers for 5v output and ground, as well as direct access to the LiPo Cell output, and a switch header to cut off power to the MH-CD42 when it is not in use.

The PCB

The PCB was manufactured as a 2-layer FR-4 board. The entire top layer is used as a ground plane, and the bottom layer was used for the 5v and Vbat traces, which were made as big as possible to allow for the high current ( up to 2A ) that the unit can supply to a load.

The BOTTOM Layer caries only power traces for 5v and VBat

a 3D Render of the PCB, showing header pins and other connections

It is also worth mentioning that the VBAT pins are NOT 3.3v ( Remember that the LiPo cell can run from 4.2v down to 3.0v depending on the charge. These headers were only placed on the board to provide direct access to the LiPo cell, for use with for example an ADC input or for connection to a dev board that is already fitted with a buck converter or a suitable LDO voltage regulator.

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.

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 $5USD 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

Compact Remote Alarm Transceiver – Part 1

As part of my experiments with LoRa and the easy to use ATMega328P, I have recently designed quite a few LoRa based projects. In this final 2 part series, I will look at two additional projects, part of a Remote Alarm Transceiver, where I experimented with a changing a few things:

– Using LM317G adjustable voltage regulators.
– Replacing my standard N-MOS based logic level converters with a dedicated chip.

LoRa Remote Alarm Transmitter – with Onboard Relay putout and two sensor inputs

How does this differ from my other LoRa Based projects?

The PCB presented above does in fact not really differ a lot from any of my existing LoRa based projects.
However, there are a few subtle changes, mainly experimental changes, brought on by factors such as component availability and an attempt to reduce component counts and board size.

The first of these changes is using the LM317G voltage regulator, in the place of my usual LM1117 3.3 and 5.0 LDO regulators.

The LM317 is an old device, It has been on the market for a long time. It can supply up to 1.5A of current, and a single device can be configured to supply a wide range of different voltages by just changing two resistors. This seemed quite attractive to me, as it is getting quite difficult to reliably get quite a few components on time, and with decent pricing in the post-Covid-19 world.

The second major change would be moving away from my existing N-Mos based Logic converter setup, where I used the BSS138 and 10K resistors as logic converters. This setup works perfectly, but it has the drawback of requiring quite a lot of components. for example:

To provide logic conversion to an RA-02 module, with access to all the IO Lines (GPIO0-5 included) required 12 BSS138 Mosfets and 24 10k resistors. This is quite a lot of components. A dedicated logic converter chip would thus be a much more attractive solution.

Driver circuitry for sensor Inputs, consisting of a simple transistor input, and an optically isolated Relay output completes the circuit.

Using the LM317

LM317 Typical use circuit - Fixed Voltage

The output voltage of the LM317 is typically set using two resistors, with a suitable current rating, using the following Formula

V_OUT = 1.25 * ( 1 + R2/R1 )

It is also common to use a variable resistor at R2, to have fine control over the output voltage. This is due to the fact that stock resistor values do not always give you the exact voltage you require. You should also take into account that using a 5% resistor will be less accurate than a 1% resistor.

The grid below is a list of common stock resistor values for R1/R2, with the resulting voltage produced.

R1 vs R2 Grid for use in selecting fixed output voltage

R2\R1	150	180	220	240	270	330	370	390	470
68	1.82	1.72	1.64	1.60	1.56	1.51	1.48	1.47	1.43
82	1.93	1.82	1.72	1.68	1.63	1.56	1.53	1.51	1.47
100	2.08	1.94	1.82	1.77	1.71	1.63	1.59	1.57	1.52
120	2.25	2.08	1.93	1.88	1.81	1.70	1.66	1.63	1.57
150	2.50	2.29	2.10	2.03	1.94	1.82	1.76	1.73	1.65
180	2.75	2.50	2.27	2.19	2.08	1.93	1.86	1.83	1.73
220	3.08	2.78	2.50	2.40	2.27	2.08	1.99	1.96	1.84
240	3.25	2.92	2.61	2.50	2.36	2.16	2.06	2.02	1.89
270	3.50	3.13	2.78	2.66	2.50	2.27	2.16	2.12	1.97
330	4.00	3.54	3.13	2.97	2.78	2.50	2.36	2.31	2.13
370	4.33	3.82	3.35	3.18	2.96	2.65	2.50	2.44	2.23
390	4.50	3.96	3.47	3.28	3.06	2.73	2.57	2.50	2.29
470	5.17	4.51	3.92	3.70	3.43	3.03	2.84	2.76	2.50
560	5.92	5.14	4.43	4.17	3.84	3.37	3.14	3.04	2.74
680	6.92	5.97	5.11	4.79	4.40	3.83	3.55	3.43	3.06
820	8.08	6.94	5.91	5.52	5.05	4.36	4.02	3.88	3.43
1000	9.58	8.19	6.93	6.46	5.88	5.04	4.63	4.46	3.91
1200	11.25	9.58	8.07	7.50	6.81	5.80	5.30	5.10	4.44
1500	13.75	11.67	9.77	9.06	8.19	6.93	6.32	6.06	5.24
1800	16.25	13.75	11.48	10.63	9.58	8.07	7.33	7.02	6.04
2200	19.58	16.53	13.75	12.71	11.44	9.58	8.68	8.30	7.10
2700	23.75	20.00	16.59	15.31	13.75	11.48	10.37	9.90	8.43
3300	28.75	24.17	20.00	18.44	16.53	13.75	12.40	11.83	10.03

As you can see from the table above, using stock resistors, the output voltage is reasonably accurate, but it is quite obvious that you will need a potentiometer to get exact values.
Another issue will definitely be heat dissipation. In my PCB design, I have used the SOT-223 package of the component, with a PCB heatsink, built directly into the layers. With the LM1117 LDO regulators, these work extremely well.

Logic Level Conversion

In this design, I used my standard Logic Level conversion circuit, comprised of a BSS138 N-Mos with two 10 k resistors. This circuit, although a bit cumbersome with lots of components if you need many logic converters, is very stable, and functions extremely well.

Conclusion

This circuit was designed as a two-part prototype, with the goal of experimenting with different voltage regulators, and in part 2, with a single chip 8 channel logic converter. As such, I do not feel comfortable releasing the full schematics to you at this stage, do so anyway in the interest of learning. The circuit works, but there are many issues with the regulators:

– Overheating at input voltages above 8.0v
The PCB heatsink will have to be improved, or even a different package for the LM317 with the possibility to attach an external heatsink.

– The voltages do not seem stable, especially on the 3.3-volt side.

Manufacturing the PCB

This PCB was manufactured at PCBWAY. The Gerber files and BOM, as well as all the schematics, will soon be available as a shared project on their website. If you would like to have PCBWAY manufacture one of your own, designs, or even this particular PCB, you need to do the following…
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4) Click on PCB Instant Quote

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