makeriot2020 - Maker and IOT Ideas

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).

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_ATTiny1616-MinimalQFN_2023-02-24 Download

Design and Assembly

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.

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

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…

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?

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_UPDI-Programmer_2023-02-17 Download

Manufacturing

Find out more here

Pictures of the PCB and Assembled Module

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

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.

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_Soft-Start-Switch_2023-01-29 Download

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

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.

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.

The 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.

Manufacturing

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.

The 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.

Manufacturing

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);
  }

Redesigning my MCP23017 breakout

In a previous post, I designed a breadboard-friendly MCP23017 breakout module. A few months have passed, and after using the module for a while, some issues came to light…

In this post, I will show you how I have fixed those issues, and then I can continue testing/using the new generation prototype, and hopefully, it can become the final revision of this project.

Old Versus New

Let us start by looking at the old and new PCB designs…

There will not be a lot of obvious differences at first, but if we look closely, here are the changes:
– In the old version, due to the size of the SOIC28 footprint, I had to place the bypass capacitors, as well as I2C pullup resistors on the bottom layer of the PCB.

The new design, using the more readily available ( at least where I live) SSOP28 footprint, leaves enough space for these components on the top layer, thus resulting in a mostly single-layer layout, with only a few tracks on the bottom layer.
I2C pull-up resistors can now be controlled by a jumper, enabling or disabling them completely… This helps when adding a few devices to the I2C bus, and rather having the pull-up’s close to the MCU ( as is generally recommended anyway )
Other cosmetic changes involve the separation of the data ports (A and B) from the interrupts, reset, Vcc and ground pins. On initial testing of this on a breadboard, it makes using the device a bit easier, and access to the io pins faster. ( In my biased opinion anyway )

MCP23017 Breakout Module — MCP23017 Breakout – New version

Pinouts and connections

I have tried to make all the connections easy to find and use, with the IO ports ( A and B) on opposite sides of the breakout, Numbered A7 to A0 on the top, and B7 to B0 on the bottom.
VCC, GND, SCL and SDA are on a separate 4-way header pin, with the two interrupt pins (I-A and I-B) together with the reset (RST) pin on a 3-way header opposite the power and signal header..

Addressing pins are in the centre of the PCB, marked with a 2 1 0 ( for AD2, AD1, and AD0 respectively), Jumpers to the bottom ( towards port B) pull the pins to ground, where the opposite side will pull the address pins high.

To the right of that, another 3-way jumper enables or disables the I2C pull-resistors on the module, which in this case is set at 4k7.

Manufacturing

Some More Pictures

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

Some More Pictures

Back of PCB, isolation cutouts clearly visible

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.