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

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);  

}

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

Easy to use ESP32-S DEV Prototype Shield

While my recent ESP32-S Dev Board really does the trick to help my development cycle along, I very quickly ran into another obstacle, in the sense that, after doing stuff on the breadboard, moving those components onto a more permanent location, either as a next stage prototype or more likely that the project is so small and insignificant not to warrant the effort actually to design a PCB for it. This could be rectified by using another one of my recent designs, an SMD breadboard PCB, but that would not always do either.

MakerIoT SMD Prototype development PCB
MakerIoT SMD Prototype development PCB

That got me thinking, and while staring at the ever-present Arduino Uno on its corner of the work-bench, I suddenly remembered that I have once seen an Arduino Prototype Shield, like a plug-on breadboard, with breakouts of all the pins etc…

While I do not personally own a lot of commercial Arduino Shields, as I tend to build my own or design a custom-purpose PCB instead, it did not take me long to settle on a new design, that could potentially solve my problem, and hopefully, someone else’s as well…

ESP32-S DEV Prorotype Shield - Unassembled, Top side

So what is on this PCB?

To start off, the PCB is in the same form factor as the ESP32-S Dev Board, namely the Arduino Uno form factor. There are however a few changes, mainly in the number of pins in the headers. This is mainly to accommodate as many of the ESP32-S’s gpio’s as possible. ( Actually, they are all broken out, EXCEPT for the 6 gpio’s that are usually used with the internal Flash memory.)

The PCB is designed to be stacked either on top of, or even below, the ESP32-S Dev Board, depending of course on the type of headers that you decide to solder onto the PCB.

In order to make connecting to the gpio pins easier, each header row is in fact a double row, with solderable pads in parallel for each gpio on the header row.

Flash and Reset buttons are available on top of the shield, they can be fitted of left off, depending on personal preference, as well as how the shield will ultimately be used.

The prototyping area in the centre has been slightly reduced from the standard 5-pin-spacer-5-pin column of the traditional breadboard to a 3-pin-gnd-3v-3-pin column layout. the prototyping holes are at a standard 0.1″ or 2.54mm pitch.

In total, 60 prototype holes, divided into rows of 10, 3 columns deep, are provided, labelled A-F and 1-10.

3.3v and ground are provided in the centre-two rows, to make power easily accessible.

ESP32-S DEV Prototype Shield
ESP32-S DEV Prototype Shield
ESP32-S DEV Prototype Shield - Back
ESP32-S Dev Prototype Shield – Back

The PCB Design

As this design is basically just two rows of header pins, with a few switches, and a big unconnected prototype area, I did not bother to do a formal schematic for this PCB, but instead jumped straight into the PCB design software and manually designed and routed the tracks and pads that make up this shield.

PCB – Top Layer
PCB – Bottom Layer – Note that this is a “TOP-Down” view, and should be mirrored for actual production

Note that there are big copper pours on both top and bottom layers, in an attemp to reduce electrical noise and provide better shielding.

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 device

Conclusion

Some final thoughts on the completed PCB.
While definitely useful, I have made a purpuseful design flaw on this board, by not including a breakout for the VIN pin. My reasoning at that stage was that I would always be powering the device directly from 3.3v, and would therefor not need access to the VIN pin for power.

Upon completion of the device, and while testing it in a stacked configuration, I realised that that VIN pin would have been quite nice to have access to.

Not a big problem though, as if is very easy to add a 2-pin connector to the power rails, or even solder a wire directly to VIN. Ugly, but totally doable, as this is in fact still a prototype, and it can grow and be fine-tuned to my exact requirements over time.

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.


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

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

4) Click on PCB Instant Quote

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

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

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

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

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

ATMega 328P Based PWM controller Card

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

What is on the PCB?

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

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

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

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

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


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

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

Manufacturing the PCB


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


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

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.

VC-01 and VC-02 Offline Voice Module

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

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

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

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

The Schematic

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

Testing the PCB

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

Manufacturing the PCB


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


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

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.

True OFFLINE Voice Assistant

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

Introducing VC-01/VC-02

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

Custom Firmware – Test 01

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

Hardware access to the real world

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

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

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

PCB Prototype – Of my own design

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

My Conclusion

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

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

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

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

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


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 TOP later of the PCB is a complete ground plane.
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.

The Actual PCB, as received from PCBWay
Top Layer of the PCB
Bottom Layer of PCB

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.

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

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

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.

Robotic Toy Car – Part 4

In this part of the series, Robotic Toy Car – Part 4, We will add some custom side-panels to the project. While the original toy did come with some laser cut aluminum side panels, I decided to replace them with PCB versions, with even more flashing lights (yes, this thing is turning into a “Christmas tree” , but that is what the eventual owner wanted… )

These side-panels will not be programmable. They will simply be operated from a standard 555 timer and a couple of other components, to give a flash time of about one second on and off each…

It is also an excellent project to showcase the capabilities of PCBWay, in dealing with a “rather difficult” PCB to manufacture. As you may know by now, I use PCBWay‘s services quite extensively, and I also only design my PCB’s with EasyEDA. EasyEDA is however quite limited in some aspects, and as far as myself, making panels of different designs on one PCB with complex shapes is not something that I do every day…

Let us take a look at what had to be done, and how well it was manufactured…

The PCB Layout

What we have here, is basically two mirrored side-panels ( as far as the visible “outside” is concerned anyway ) That consists of 6 led’s per side that will flash alternatively. On the “inside” we have a 555 timer chip, with some resistors and capacitors, as well as transistors that does the switching.

The Schematic

The difficulty of this PCB is definitely in the manufacturing. I was however pleasantly surprised with the excellent work that was done by PCBWay. Their Engineering staff did contact me early on in the order, with a suggested plan to manufacture, and once I approved that, they very quickly went on to production. My initial concern was that they suggested “mouse-bites” which we all know can sometimes come out a bit strange…

Completed PCB in packaging..

I was however extremely pleased when the above parcel arrived… They added side rails, and the “mouse-bytes” were super tiny.

After assembly ( not cleaned up yet )
After Assembly ( not cleaned up yet )
Installed on the toy car body

The “almost completed ” Robotic Toy Car

With the completion of the side-panels, it was also time to start work on the power wiring and other essential components of the project, which will get their own detailed post in a few days.

the “almost completed” project

Some details on the construction:
The toy originally came with a single 500mA 14500 cell, which unfortunately stopped working very soon after only a few uses… This was however one of the reasons why the entire project happened in the first place, so no complaints there.

I decided to replace it with a 18560 cell with a capacity of about 1900mA. This cell is much bigger however, and I had to think of where to place it. I decided to put it on the roof, sort of emulating a “spoiler”.

Some of the next parts of the project will be the remote control unit, which will basically be an ESP8266 running ESP-Now protocol, as well as a decent battery charging and power distribution circuit, that will protect the Lipo cell from over charging and discharging, as well as provide sufficient power for all the added electronics in the toy car.

“But you said it was Robotic, so why have a remote control?”

The initial plan for the project did indeed say robotic, but it is also designed to be a learning platform, especially to teach coding. With that in mind, it is definitely better to keep things simple for now, and add sensors and more capabilities later on, especially as I am actually planning to replace the main MCU board with a more powerful ESP32 in a next version anyway.

The car body is also extremely cramped, and does not have any space for mounting sensors at all. I plan to remedy that by designing and 3d-printing a whole new custom body shell later… providing that my young friend actually stays interested enough to learn the coding… If he doesn’t, he will as least have a very interesting looking custom remote controlled toy car.

Manufacturing the PCB

The PCB for this project is currently on its way from China, after having 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 be manufactured.

PCBWay

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

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.