Category: Custom PCB Design

Breaking out of the Chip Shortage – Attempt #3

The ATMEGA4808 provides a very attractive solution to replace the trusted ATMEGA328 or standard Arduino UNO /NANO.

These chips are slightly more difficult to get hold of than the ATTiny chips, and cost a little bit more ( about the same as what the ATMEGA328 used to cost before the mess with COVID-19 and resulting supply chain shortages + inflated costs), but they offer all of the functions of the ATMEGA328, with a few other enhancements that will definitely be very useful.

The extras include:
– Hardware interrupts on ALL GPIO pins; This is way more than the standard 2 interrupts on the ATMEGA328 ( We are not talking about the Pin Change interrupts, but real hardware interrupts, that can be triggered on RISING, FALLING, CHANGE, HIGH and LOW state of each pin

– Up to eight (8) PWM pins as opposed to the 6 on the Arduino UNO
– Up to eleven Analog inputs
– An Analog Comparator module
– Configurable Custom Logic (CCL)
– EVENT System (EVSYS)
– Peripheral pin swapping

It is also worth mentioning that these chips have accurate internal oscillators, capable of clocking the chip at up to 20MHz, further reducing the number of external components required to get a minimal configuration running…

Order your own version of this development board

The Prototype PCB

While I have had a Nano Every “Clone” lying in a drawer for quite a while now, I did not really pay a lot of attention to it. That was, until I needed an ATMEGA328 for a project, and could not find any for sale, or at least at a price that I was willing to pay for it… That incident was the spark that ignited this entire exercise, to find a suitable replacement…

The Nano Every “Clone” in my possession, used the ATMEGA 4808 chip and turned out to be the Thinary Nano 4808. I had quite a lot of problems with the provided core, as well as getting peripherals like I2c and SPI to work. This led to further investigations, and finally, I decided on building my own and to use the MCUdude/MegaCoreX Arduino Core to program it.

This led to the following prototype:

ATMEGA4808 Development board prototype

I did not bother with too much detail on the silk screen here, as the goal was to get a working board, test it, and then later, design a refined PCB.

What is important to note is that the board runs at 5v, but provides a single 3.3v output as well. Logic levels on the GPIO is also 5v. Use level converters for 3.3v only addons…

The MEGA4808 is programmed via UPDI, so we have a UPDI Header on the right-hand side of the PCB. It is also possible to use the Optiboot Bootloader, to flash the board in true Arduino style through a USB connection to a computer.

A CH340N USB-to-Serial converter chip is used instead of the CH340G that is common on the UNO clones. The CH340N provides only the USB D+ D- signals, as well as Rx, TX and RTS. RTS is being used to auto-reset the chip after flashing…

In comparison to the CH340G, which also required a crystal oscillator, but provides all the modem control signals, which, are usually not even broken out, the CH340N made much more sense.

PCB Bottom.

A power LED, as well as an indicator LED on pin 7 was also included.

Assembled PCB, Top Layer.

Assembly and Soldering

I normally assemble all my projects by hand and reflow-solder them with a hot plate. for this project, I decided to do things a bit differently, which ended up being a bit awkward, but still resulted in a perfectly useable PBC.

As you will know by now, I only do written articles, as I don’t consider myself ready for the Youtube and video thing, as well as because I believe a well-written article, with detailed pictures, is easier to understand than a video…

Well, today, we will have both… This article, with its writeups and pictures, as well as a short assembly and soldering video, with no sound, sped up 5x, as I did not want to bore anyone with a 25-minute silent video…

Let us begin then…

PCB and Stencil

We start with a blank PCB and the laser-cut stainless steel stencil that I got from PCBWay.

Solder paste applied

Solder paste is then applied with the stencil and a scraper, and afterwards, the stencil is removed… The PCB is now ready for component placement…

From here on, we will go to the video footage… showing component placement, with some awkwardness due to the camera being in the way, as well as hot-air soldering, with the same awkwardness, as I was forced to use my right hand ( I am left-handed), not to block the camera view…

Begin quite new to the video thing, I have also not quite figured out the editing software, so the video is in native resolution… not zoomed…

After assembly

After assembly, I checked for solder bridges and was quite happy that there were none. This also meant that the board worked perfectly the first time around… as it should…

Order your own version of this development board

Manufacturing

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

Blank PCB – Top
Blank PCB – Bottom
PCB and Stencil
After Solderpaste application
After assembly, inspection
After assembly, inspection
Completed PCB, Top
Completed PBC, Bottom

Breaking out of the Chip Shortage – Attempt #2

The ATTiny1616 is a step up from the ATTiny202, having more GPIO, flash and RAM. This makes it ideal for bigger, but still medium size projects that do not need all the power of the traditional Arduino.

In Part 1 of this series, I took a quick look at the ATTiny202 MCU from Microchip. Having only 5 useable GPIO, with limited Flash and Ram, that little chip was still quite useful for some of those very small projects, where we did not really need a lot of peripherals and GPIO pins.

Today, we shall take a step up, and take look at a slightly bigger MCU, the ATTiny1616, this time with up to 17 GPIO pins, more flash and memory, and still quite easy and cheap to get hold of. (Current Prices are in the range of about $1USD to $2USD, depending on where you buy and how many you buy).

As I wanted to give myself a bit of a challenge with this project, I decided on using a QFN package this time, which, being extremely tiny, only 3mmx3mm, will give most Makers a pleasant challenge to solder correctly. ( I am planning a SOIC 20 version, but with a bit more external hardware onboard)

MakerIoT2020 ATTiny1616 Minimal Breadboard-friendly breakout

The ATTiny 1616 is part of the tinyAVR-1 series, which includes the 1614,1616, and 1617, and they have the following features ( copied from the datasheet link above)

The ATtiny1614/1616/1617 are members of the tinyAVR® 1-series of microcontrollers, using the AVR® processor with hardware multiplier, running at up to 20 MHz, with 16 KB Flash, 2 KB of SRAM, and 256 bytes of EEPROM in a 14-,20- and 24-pin package. The tinyAVR® 1-series uses the latest technologies with a flexible, low-power architecture, including Event System, accurate analog features, and Core Independent Peripherals (CIPs). Capacitive touch interfaces with Driven Shield+ and Boost Mode technologies are supported with the integrated Peripheral Touch Controller (PTC).

ATTiny 1616 Breakout – Bottom view

The PCB – Minimal working configuration – with a few extras

The PCB break-out all 18 of the GPIO pins, while it is only recommended to use 17 of them, unless, like in the case of the ATTiny202, you have access to an HV UPDI programmer. It also becomes possible, although still being quite tedious and awkward, to use the OptiBoot Bootloader on this chip, although it is still not quite recommended. Just using a UPDI programmer, with a separate USB-to-Serial adapter on another port is still definitely the easiest.

The Board contains an LED, on PIN_PA4, Arduino Pin 16, as well as onboard I2C pull-up resistors, selectable via a jumper. It is important to note that the current version DOES NOT contain a voltage regulator on the PCB. It is up to you to provide a regulated voltage source, in the range of 1.8v to 5.5v DC

It is recommended to clock the Chip at 16MHz when running at 5v ( 20Mhz is possible, But I did not bother to test that yet)
8Mhz when running at 3.3v
0-5Mhz when running at 1.8v

See the Datasheet, as well as the megaTinyCore documentation for exact details on this.

Commonly used peripherals, by myself, are listed on the back of the PCB for easy reference.

Order your own version here.

Programming the board

Programming is possible with Arduino IDE (and platformIO, ( I didn’t test that, as I find VS-Code tedious to use ), as well as MPLab from Microchip.
For the Arduino IDE, you have to install the megaTinyCore Arduino Core, as already mentioned above. ( This also apparently works for PlatformIO)

Full instructions, as well as some very useful other tips and information, is available in the core documentation, so do put in the effort to actually read the documentation. You won’t be sorry that you did.

The Schematic

Schematic
Schematic_ATTiny1616-MinimalQFN_2023-02-24Download

Design and Assembly

PCB layout

The board is designed as a double-layer PCB, with ground planes on both sides.

Due to the MCU package having a QFN footprint, using a proper SMD stencil is strongly recommended.

SMD Stencil – Make things a bit easier.

Hot-Air or a hotplate will also be quite useful to ensure success with this project. Passive components can be hand soldered though.

Manufacturing

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

PCB Top
PCB Bottom
PCB Top – Assembled
PCB Bottom – Assembled
ATTiny1616 Breakout on breadboard
ATTiny1616 Breakout, with MakerIoT Multipurpose UPDI Progammer on Breadboard, running blink sketch

Small and Cheap UPDI Programmer

UPDI programmers are a new necessity in my lab, as I continue my quest to find a suitable replacement for the old Atmega328P chips (More on that in another post). In a previous post, I showed you a combination UART/UPDI programmer module that I have recently designed. It would only be fair to show you where that started out, as a single-purpose UPDI programmer, based on the CH340N.

The CH340N has, according to me at least, some advantages over the CH340G in the sense that it requires very few external components, most notably that it doesn’t require an external crystal oscillator. It does however NOT provide you with all the Modem signal lines (RTS, DTS, DTR, CTS etc) that you get on the CH340G, although most people will not use most of those anyway…

The cost of the two chips is about the same, with the CH340N being slightly more available at the moment, at least in my part of the world.

The particular circuit that I am using originated from Stefan Wagner. I simply designed my own PCB around his circuit. Credit is given where it is due, as I found his site, and content extremely detailed and accurate.

While this is a serial UPDI programmer, with NO HV capability, I do find it extremely useful as a test project, and while I may invest in a proper HV UPDI programmer in the future, if the bigger part of the project plays out the way I anticipate, for the time being, this is exactly what I need.

Order your own here

What is on the PCB?

3D Render of the UPDI Programmer

The PCB is quite small, with a low component count, 6 capacitors, 4 of which is smoothing capacitors, two resistors, one Power on LED indicator, a 3.3v voltage regulator, USB connector ( Type B Mini) and of course the CH340N and a few header pins, one of which is used as a target voltage selector by means of a jumper. I did not bother with a switch as this pushes the cost of the device up by quite a bit.

Current costs for the components are around 5USD excl shipping at LCSC.

So, J1 is used to select the target voltage between 3.3v and 5v.
The other header provides VCC ( marked V+), GND and the UPDI output.

The Schematic

Schematic
Schematic_UPDI-Programmer_2023-02-17Download

Manufacturing

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

Pictures of the PCB and Assembled Module

3D Render of the PCB
UPDI Programmer
Assembled PCB
Blank PCB, Stacked
SMD Stencil for assembly
Top Side
Bottom Side

Assembly

I assemble all of my projects by hand, using hot air and or a hotplate for reflowing. Having an accurate stencil for applying just the right amount of solder paste becomes a necessity very quickly.
In future, I plan to have a dedicated section showing the assembly of some of the more challenging boards…

Multipurpose USB UART Module

USB-to-Serial converters are some of the most used modules on my bench. I have quite a few of them, most of them are the cheap online type that can be had for a few dollars.

As part of my new project, where I am seriously looking for an alternative chip to replace the ATMEGA328, which has become almost impossible to get, and super expensive when you do get it, I needed to get hold of a UPDI programmer.

There are many available online, from cheap to more expensive, but I wanted to build my own, as it did not seem too difficult to do.

As another part of my daily tasks, I also use a lot of ESP-type chips, which have a particular procedure to upload code via an external serial adapter.

The idea was thus to design a USB UART module that has multiple purposes, as well as being easy and cheap to assemble.

  • Be able to program ATMEGA328 Chips via Serial
  • Be able to be used as a standard USB-to-UART adapter
  • Be a UPDI programmer
  • Have a selectable target voltage between 3.3v and 5v
  • Have all modem signals (RTS, CTS, DSR, DTR) broken out.
  • Be able to auto-flash and reset an ESP32 or ESP8266 device, or similar
Breadboard Prototype Multipurpose USB-to-UART/UPDI Programmer

What is on the PCB?

The PCB is powered by the PC USB port. The target device voltage is selectable between 3.3v and 5v. The device mode can be changed from UART to UPDI mode with a jumper. An additional header specifically for ESP32/ESP8266 devices is provided, giving access to the FLASH and reset signals for the ESP device.

The USB to serial conversion is taken care of by a CH340G Chip, which provides all the relevant modem signals as well.

All signals, with the exception of the “RING” signal, are broken out onto the main header.

Note that there are NO status or POWER LEDs on the board. This was on purpose, as these sometimes interfere with the UPDI programming mode.

Prototype PCB – Assembled

PCB – Top
PCB – Bottom

Connecting to different devices

ESP32 or ESP8266 Devices

When in UART mode, the device can be used to upload code to an ESP32/ESP8266 automatically, similar to a standard dev board, without requiring you to press and flash and reset buttons.

This is achieved by connecting the device as follows:

UART MODULE SET to 3v
UART VCC to ESP 3v
UART GND to ESP GND
UART RX to ESP TX
UART TX to ESP RX

(Connections for Auto Upload/Reset)
UART RST ( on ESP-Flash Header) to ESP RST
UART GPIO0 ( on ESP-Flash Header) to ESP GPIO0

It will now be possible to flash and auto reset the connected ESP device from the Arduino IDE, and possibly others as well…

Arduino (Atmega 328P)

In the current version of the prototype, you have to connect it as follows:

UART Target voltage set to 3v or 5v depending on what type of board you are uploading

UART Tx to Arduino Rx
UART Rx to Arduino Tx
UART VCC to Arduino 3v or 5v ( depending on the target voltage required by the board you are flashing)
UART GND to Arduino GND

To allow for auto flash/reset on the Arduino, a 100nf capacitor is required between the UART DTR line and the Arduino Reset pin. This capacitor has NOT yet been fitted onto the PCB, as I usually use ICSP to upload these. Future versions of the PCB shall have this included.

ATMEGA4808/4809 and or ATTiny with UPDI Interface

This device is currently an LV-only UPDI programmer. Connections are as follows:

Set Target voltage on J1 of the UART/UPDI programmer.
Set The Device mode on J2 to UPDI mode

Connect VCC and GND from the Programmer to the target chip/board
Connect Programmer UPDI pin( shared with RxD) to Target UPDI pin.

General use UART for use as Serial monitor/Terminal

Set target voltage on J1
Set device mode to UART on J2

Connect VCC, GND from UART to the target device,
UART Tx to Target Rx
Uart Rx to Target Tx

Optionally connect required modem signals, RTS, CTS, DTR, and DSR as needed

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.

PCBWay

Some Links to things used in the project

MakerIoT SMD Prototyping Breadboard
Order this PCB from PCBWay

A Soft Start Circuit Experiment

Every single project that we build needs an On/Off switch. Hardware switches are big and clumsy and can be quite expensive. Most of them also don’t look very good.

This post will be about an experiment that I recently performed, building a reliable soft start circuit, or latching circuit.

Full disclosure: I did not design this circuit. Full credit to the designer, who shall be mentioned later.

As such, This shall be about my experiences with this great little circuit, and also to show off the neat little prototype PCB that I designed and had manufactured for this experiment. It only took a few minutes to design, and even less to assemble.

The Schematic

Schematic
Schematic_Soft-Start-Switch_2023-01-29Download

How does it work?

To answer this, let us look at what components are in the circuit first.
Q1 is a P-Channel Mosfet. I chose the SI2301, because that is what I had lying around.
T1 and T2 are NPN BJT transistors, I chose S8050’s here, and also tested 2n2222a’s with great success.
Other components are 3 100k pullup resistors, 1 1M pullup and an 1k dropper resistor for the indicator LED.

In the off state, R1 (100k) keeps the gate of Q1 tied to the supply voltage, thus keeping the MOSFET switched off.
T1’s collector, also connected to the MOSFET Gate, are thus pulled High, with the Base of T1, although pulled High, connected to the Drain of Q1.

Q1 is still off, so that base will be low, for now at least.

The collector of T2, is pulled up to the supply voltage via R4, and also, through the push button, to the base of T1.

The base of T2, is pulled up via a 1M resistor to the drain of Q1, and a 22uf to 47uf electrolytic capacitor to ground.

The emitters of both T1 and T2 are grounded.

When you press the switch, the base of T1 goes high, and this switches T1 on, pulling the gate of Q1 to ground, switching it on. This now pulls the base of T1 high through R2, latching it on, and keeping Q1 switched on. This also pulls the base of T2 high through R3. As T2 is now also switched on, the junction between the collector of T2 and the switch is now for all purposes a ground.

Now, when you push the switch again, the base of T1 is pulled down to ground via T2. This switched off Q1. As the capacitor on the base of T2 can now discharge, the circuit is reset, and the next press of the switch will turn it on again.

How big a load can be switched?

Obviously this depends on the rating of the MOSFET at Q1. In my experiments, a load of about 150mA was easily controlled, but more than that, started to somehow drain the cap at C1 too fast, and the circuit would reset.

This is not a problem to me, as the circuit is ideal to switch a relay, which in return can switch the main load.

What other issues did I encounter?

The SI2301 seems to have a small amount of leakage, which allowed a few millivolts to activate T1 or T2. I solved that with the addition of a 10k pulldown to ground, on the base of T1.

This does not seem to be the case with other MOSFETS, and I believe changing the value of R1 to provide a stronger pullup, might solve this issue.

Where does the circuit come from?

I found the circuit, and explanation on the excellent Youtube channel EEVBlog.
The owner, Dave, does an excellent job of explaining how this works. All credit to Dave for this excellent circuit!

It has zero current consumption in the off-state, and very little when on.

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.

PCBWay

Conclusion

I believe this is a great little circuit to keep around, with many excellent use scenarios. It does need a bit of fiddling to get to work perfectly every time ( as you can use many different P Channel Mosfets and NPN BJT transistors)

It provides an excellent alternative to a mechanical switch, and for my own use, the PCB Module is small enough to be mounted into an enclosure with another project with ease.

8Ch NMOS Breakout Module

As a companion module to my recently published 8Ch PMOD breakout board,
I decided to do a similar PCB, but with NMOS devices instead. This opens up more possibilities for proper testing and prototyping, as PMOS and NMOS devices has different use applications, and most importantly, can sometimes even be combined for a particular purpose, like an H-Bridge motor driver, for example.

8Ch NMOS Breakout

What is on the PCB?

As NMOS devices function quite differently from their PMOS counterparts, it did not make sense to reuse the PMOS board, and just change the devices… although some people may be tempted to think you could…

The N Channel Mosfet basically “works in mirrored mode” from a P Channel one, and is used to do so-called ” LOW Side switching” which means that your load connects to the positive power rail, and then to the DRAIN pin of the MOSFET, with the source being connected to ground… ( It can sometimes also be used the other way around… but lets not go there now….

The current prototype PCB contains 8 BSS138 NMOS Mosfets, in my case, with is capable of about 800mA of current… All source pins are internally connected to ground. This forces you to use this module as a low side switch…

Two 10-way 2.54mm headers are provided, with a ground pin on Pin 1 and 10 of each of these.

The Drain pins of each NMOS device is available on the top header, labeled D1 through D8, and the Gate pins of each respective NMOS device is available on the bottom header, labelled G1 through G8.

Each gate has a pull-down resistor to ground, to keep it from flapping around, as well as a gate resistor. In my case, I selected to use a 10k pulldown, and a 1k gate resistor, as that is sufficient for my general needs…

Each NMOS device also has a LED signal indicator, to assist in visual confirmation of a specific channel’s state.

PCB Top Side

The Schematic

Schematic

Using the breakout

The module is very easy to use, and as briefly mentioned above, you are only required to connect one side of your load to the positive supply rail, and the other side to the drain pin of your choice.

Connect the ground pins of the module to your ground rail.

The Gate pin, with a corresponding number to the drain you have selected, can now be connected to your GPIO of choice on a microcontroller.

Drive the pin High to switch on the load, drive it log to switch off. Easy.

Please note: While the NMOS devices used on the board can handle quite a lot of current, (800mA in the case of the BSS138), it is not recommended to try and pull too much current through a single channel. The PCB traces can safely handle about a maximum of 300 to 400mA per channel.

PCB Bottom

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.

PCBWay

Example code for using the breakout (Arduino)

// Example code for 8Ch NMOS breakout
int Gate1 9;
int Gate2 10;

void setup() {
  // drive the two gate pins low to ensure NMOS devices
  // are in a positively known state at startup
  digitalWrite(Gate1,LOW);
  digitalWrite(Gate2,LOW);
  // Set gpio to output mode
  pinMode(Gate1,OUTPUT);
  pinMode(Gate2,OUTPUT);

}

void loop() {
  // Toggle the two channels in an alternating pattern
  digitalWrite(Gate1,!digitalRead(Gate1));
  digitalWrite(Gate2,!digitalRead(Gate1));
  delay(1000);  

}

8-Ch P-Mos Breakout

While prototyping our projects, we Makers often need to interface devices with a higher current draw, like motors, or RGB lights, to our microcontrollers. These typically are unsuitable for connecting directly to an Arduino, ESP32 or Raspberry Pi’s GPIO pins. This is usually the time when we start grabbing transistors or MOSFETs.

While I normally keep a few leaded transistors and MOSFETs in the lab, These are not always convenient to use, as they may be in big packages or have the wrong specifications for the task that we are trying to perform.

SMD versions are more common in my lab, but they come with the problem of being small, and also completely unfriendly to the breadboard environment.


I have thus been playing with an idea to make a series of dedicated breakout boards for just this purpose. Having an easy way to test a specific MOSFET for a design, and having more than one of them handy, without all the wiring issues, and using the bare minimum of those DuPont wires!

I came up with the following prototype, which, while not completely optimised yet, already makes things easier. The breakout board provides 8 P-Channel Mosfets, with a single source connection, and individually broken-out Drain and Gate pins.

LED indicators on each channel provide a visual indication of the status of each P-Mos device, and the breakout can also be mounted directly into an enclosure if needed.

What is on the PCB?

Each channel comprises a P-Channel Mosfet, in this case, a SI2301, which has a suitably low gate voltage, a pullup resistor on the gate, to keep it from floating, a status-indicating LED and a current-limiting resistor for the LED.

No gate resistor was added, as this would change depending on the actual MOSFET, as well as the microcontroller that you use. The Gate pullup resistor can also be left unpopulated, in case you need to do something specific there.

Two rows of 10-way, 2.54 header pins are at the top and bottom of the PCB, to make using the breakout on a breadboard possible.

The Pinouts are as follows

H2 – Top V+ D1 D2 D3 D4 D5 D6 D7 D8 GND
with Dx corresponding to the Drain pin of each MOSFET. All the Source pins are internally connected together, as I assumed that I will use the same source voltage on each channel anyway.

H1 – Bottom V+ G1 G2 G3 G4 G5 G6 G7 G8 GND
with Gx corresponding to the gate pin of each MOSFET.

V+ and GND for each header is internally connected, to make it possible to supply V+ and Gnd on any of the two headers.

PCB Top Layer

The Schematic

Schematic

Using the Breakout

Using the breakout is straightforward. Connect a source voltage to either of the V+ pins and Ground to either of the GND pins. ( the ground is used internally for the status LEDs)

Connect your load, with the positive to a drain pin, let us say D1, and the load ground to your breadboard, or power supply ground. Connect the corresponding gate pin, in our case G1, to the microcontroller pin of your choice, through a suitable gate resistor, and pull it high at setup, to ensure that the MOSFET stays off. Pull low to activate as needed.

Please note that you should not try to switch excessively large currents through a single MOSFET Channel, as the PCB traces can realistically only handle approximately 300 to 400mA per channel.

Note 2: If you are driving an inductive load, it is considered good practice to add a flywheel diode on the load as well. This will protect the MOSFET from back EMF when the MOSFET is switched off.

PCB Back

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.

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Example code for using the breakout (Arduino)

// Declare Gate driving GPIO pins
int gate1 = 10; 
int gate2 = 11;


void setup() {
// Set the GPIO pins as outputs and drive them HIGH
// This keeps the channels switched "OFF"
  digitalWrite(gate1,HIGH);
  digitalWrite(gate2,HIGH);
  pinMode(gate1,OUTPUT);
  pinMode(gate2,OUTPUT);

// Writing to the GPIO's before setting their pin Mode,ensures that the
// GPIO's are in fact initiated in a know correct state.

  Serial.begin(115200);

}

void loop() {
// In the loop, we just toggle the GPIOs, thus
// alternatively switching the channels on or off
  digitalWrite(gate1,!digitalRead(gate1));
  digitalWrite(gate2,!digitalRead(gate1));
  delay(1000);
  }

Dual 555 Latching Switch Module

In a recent post, I looked at a single-channel version of this module. While it may be a repetitive post, I will continue, as it shows how easy it is to double up on this circuit to provide more than one latching switch on a single circuit board. The current drawn by this module is so little, even when energised, that it compares favourably with even a microprocessor-controlled solution.

The real advantage will obviously be the cost, as the hand full of discrete components needed for this is way cheaper than a microprocessor alone, and the fact that it doesn’t need any coding makes for an attractive solution.

It is however worth noting that the circuit is quite sensitive to external interference, sometimes resulting in unwanted operation. This does not concern me too much, as 1) This is still a prototype and 2) While it does work as intended, and surely is quite useful, I do not intend using it to switch any high current load, or control any expensive or important equipment.

Since the previous post looked at the base circuit in detail already, I think it will be a good idea to talk a bit about electrical isolation, tracking and keeping the AC and DC sides of a circuit separated completely

In the picture above, we can clearly see that the DC side (near my hand, at the top is contained completely on the right side (top in this case) of the PCB. The hashed copper pour also stops clear of the two relays. There are only four tracks
going to the relay coils, and they are all on the same layer of the PCB.

Also note the square cut-out slot around the common terminal of each of the relays. This provides additional isolation to the relay, as well as the DC side of the circuit, as air is a very good insulator ( at least for 220v at no more than 10A — or so I was taught …) These cutouts will prevent any mains voltage of tracking, think burning towards, towards any other tracks in this area.

The entire left-side top layer ( underneath the relays) are also completely free of copper, to make tracking even more difficult.

If we now look at the bottom layer of this same PCB, we will see that the DC side and its ground-plane are once again completely separated from the relay contact terminals. Also note that the tracks connecting the screw-type connector and the relay terminals are very thick (100mil), straight and as short as possible. All copper around these tracks has also been etched away, further reducing the chances of tracking.

In a production PCB, Warning labels would also be present in the bottom silkscreen of the PCB in this area, warning the user of the possibility of mains voltage in this area. As this is a prototype, and to make the above-mentioned points easier to see, I have not added these labelling on these boards.

Important Disclaimer:
Electricity is NEVER “SAFE”. There are only safe practices and procedures. It is always the responsibility of the user to ensure their own safety. While the design shown above is considered “SAFE” by myself, I only consider it “SAFE” because I am aware of the risks involved in using such a circuit to switch mains voltage, at a certain current, and under a specific use scenario. DO NOT BE FOOLED into simply replicating this circuit, or parts of it, and believing it is “SAFE”. Every use case of a circuit is different, and the devices connected and controlled by it will always differ. Make sure that you ACTUALLY know what you are doing BEFORE using any High voltage/Current and switching it with any electronic device.

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.

PCBWay

Some More Pictures

Back of PCB, isolation cutouts clearly visible

AI-WB2 and XIAO RP2040 Combo

`Ai-Thinker (#notsponsored) should be quite well known to many makers as a company that manufactured and designs many of the modules that we use in our projects. We, MakerIoT2020, definitely make use of quite a few of their products, like the RA-02, as well as their ESP32-S module.



A few months ago, I got the opportunity to play with one of their newest projects, the AI-WB2, which is based on the BL602 Risc-V Chip. After a very very bumpy ride, mainly due to the chip being quite new, and documentation being virtually nonexistent in the English language, I decided to take a step back, and stop trying to reinvent the wheel 🙂 Afterall, I don’t want to use Apache NuttX or a similar RTOS for every project, as the thought of having to write almost all of the different required components from scratch, does not really appeal to me. especially as the SDK is in Chinese, and the English version of it is a bit patchy, to say the least…

This made me quite a bit frustrated, at least until I decided to change my thinking, and take a look at the stock AT command set that comes shipped on the modules from the factory… While excellent for use as a WiFi modem, it did not seem to allow any access to any of the GPIO on the WB-AI2 module… But wait… is that really a problem? No… Let me tell you why…

I also have a few XIAO Modules ( the RP2040 and SAMD21 ) lying around, and those do not have any connectivity options onboard…

A few very quick tests later, It was clear that the AI-WB2 will be a very compact
WiFi as well as BTLE connectivity solution for these XIAO modules, and, If I design with the future in mind, the GPIO pins of the AI-WB2 module can also become useable to me as well… once the firmware and SDK gets more accessible..

What followed from this is a very basic prototype PCB, with the XIAO RP2040 as the main processor, and the AI-WB2-12F as a “connectivity co-processor”, meaning that all communications functions will be offloaded to the AI-WB2 and the results of those, sent back to the XIAO for processing…

This in itself presents quite a few challenges, especially on the communications handling, and using the second UART port, which is currently not possible with the official Arduino Core for the RP2040… Luckily, the XIAO RP2040 uses an alternative core, that supports the second UART port quite well …

What is on the PCB?

AI-WB2-12F XIAO Combo

The Top Section of the PCB is dedicated to the AI-WB2-12F and its supporting components, including a flash and reset button. The GPIO for the WB2-12F is broken out onto H1.

At the right, below H1, is a series of jumpers, connecting the Xiao RP2040 and WB2-12-F Uart ports, or, alternatively, connecting the XIAO Rp2040 to the pin headers at the side of the PCB.

The rest of the PCB is dedicated to the Xiao RP2040 or Xiao SAMD21 module, with its supporting circuitry, and a dedicated Reset button for the SAMD21 module ( also works for the RP2040)

The board is powered with 5v DC through a dedicated header at the left bottom. This directly powers the Xiao and indirectly powers the WB2-12-F through a 3.3v LDO Regulator. Please note that although the Xiao is powered via 5v, the GPIO pins are all 3.3v logic!

The Schematic and PCB

Schematic
Schematic_XIAO-AI-WB2_2022-12-28Download

PCB Layout

Software

MQTT Connection on the AI-WB2-12F

AI-Thinker Example

The full AT command set example is available here

For the Xiao RP2040, like I used, it is possible to use the second UART to connect to the AI-WB2 chip.

As I am still not completely done with my development, I will not release the full code at this moment.

I have also been informed by AI-Thinker that a new version of the AT-command firmware is available that will allow using the GPIO on the AI-WB2 via AT Commands. I am currently investigating that new version, and that is also a big reason for not releasing any code at this stage.

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.

PCBWay

More Pictures

Useful ESP12E-DEV Prototype Shield

ESP-12E 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

Top Layer Layout
Bottom Layer Layout

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

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

PCBWay

Some More Pictures of the PCB

Side by side with ESP12-E Dev
Top “Through” view
Side View
Stacked view
Blank PCB, Back
Blank PCB, Front
Assembled PCB, Back