Pixelbot PCBs at the May 1st Hardware Meetup

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The coloured pins make it much easier to see what each connection does

The Hull Pixelbot is going from strength to strength. The original device was powered by an Arduino Uno running a thing we call HullOS. Late last year we ported HullOS to the Raspberry Pi Pico. To make it easier to connect (and to add some interesting new options) Brian has designed a PCB that provides a proper power supply for the PICO and exposes all the connectors for motors and sensors. We’ve also got space for an OLED screen and a couple of push buttons.

This is a major development for Pixelbot. It means that we can expand Python-Ish (or maybe even replace it with “real” Python). It certainly gives us a lot more options when building robots.

Brian used a tiny hotplate to install all the surface mount components. We’ll have the hotplate and some components at the next Hardware Meetup so you can actually watch a circuit board being soldered.

Person Sensor Powered Paparazzi

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I’ve found a use for my broken camera collection. I’m going to create a “paparazzi machine” using a person sensor from Useful Sensors. The person sensor is a tiny camera with a processor which you connect to your microcontroller using i2c. It tells the number and position of faces that it can see in the frame.

The plan is to take one of my slightly less broken cameras (one with working lens movement) and put it on a mount that lets it move towards a face and then trigger when it sees someone in front of the camera. I’m going to use a Raspberry Pi PICO to control it. Should be fun.

Stop your Circuit Python devices showing up as a disk drive

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Click the image to watch the video….

Got a message from Chris over on YouTube. He’s built my PICO Chord Keyboard design (it worked - phew) and he was wondering if there was a way to stop it appearing as a storage device each time it is plugged in. This is a very useful feature of Circuit Python - it’s how you get the program code onto the device - but it can be irritating, as well as giving folks access to your device that you might not want. I sent a reply and then I thought I’d share it on the blog:

You can stop the device appearing as a usb storage by editing the boot.py file (or adding one if it is not there) on the device. Put the following in there: 

import usb_cdc
import board

# Disable USB mass storage
storage.disable_usb_drive()

This should stop the device appearing as a file-store. But remember that if you do this it will be tricky to update the code in the device. You'd have to wipe the EEPROM to get your PICO back to a state when you can change the files.

More details here: https://docs.circuitpython.org/en/latest/shared-bindings/storage/index.html

Effortless Debugging with Your Pico Probe: No More Sudo!

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Hey there, Raspberry Pi enthusiasts! Are you tired of summoning sudo every time you need to commune with your Pico debug probe? Fear not! Today, we're delving into a nifty trick to make your Pico probe obedient without the superuser incantations. And for those of you using Visual Studio Code, this trick is a game-changer.

Why Bid Farewell to sudo?

Summoning sudo for debugging is like wearing a full suit to a casual brunch; it's overkill and can be risky. Moreover, when you're using elegant tools like Visual Studio Code, running the debugger as a superuser inside the tool is a bit tricky. Let's simplify this, shall we?

The Power of udev Rules:

In the Linux realm, udev rules are like spells that control how the system interacts with various devices. By crafting a specific udev rule, we can grant ourselves permission to access the Pico debug probe without escalating our privileges to the superuser level.

Crafting the Universal Pico Probe Rule:

Most Pico debug probes share the same Vendor and Product IDs, so we can usually use a standard rule for all. Here's how to do it:

The Magic Numbers: For the Pico debug probe, the typical IDs are: Vendor ID 2e8a and Product ID 000c. We'll use these in our rule.

Creating Your Rule: Head over to /etc/udev/rules.d/ and conjure a new file called 99-pico-debug-probe.rules Sprinkle the following line into it:

SUBSYSTEM=="usb", ATTRS{idVendor}=="2e8a", ATTRS{idProduct}=="000c", MODE="0666"

This incantation essentially tells your system, "Hey, let everyone read and write to this device, will you?"

Enforcing the Rule: To make the rule take effect, use this spell: 

sudo udevadm control --reload-rules && sudo udevadm trigger


What If My Device Is Different?

Got a different device? No problem! Plug it in, run lsusb, and look for the ID format VendorID:ProductID. Use these values to create a custom rule.

Post-Reboot Harmony:

Your new rule is like a loyal house-elf, diligently working after every reboot, ensuring smooth, sudo-free access to your debug probe.

Conclusion:

And there you have it! A simple yet elegant solution to make your debugging sessions with Raspberry Pi Pico as smooth as butter. No more sudo, no more hassle, especially when you're working in sophisticated environments like Visual Studio Code.

Happy debugging, and may your code be bug-free!

Author’s note: I didn’t write this. ChatGPT did. I worked with ChatGPT to solve my problem and then asked it to write a blog post about the solution “In the style of Rob Miles”. I’m quite proud of this, although I didn’t do much of the work….

PICO Powered Pixelbot now with Wi-Fi programming

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Just plug your Pixelbot into your computer to set up the network

The latest version of the Raspberry Pi PICO Powered Pixelbot (I love a bit of alliteration) now supports Wi-Fi programming. You can connect your robot to your local network and then use a web interface to create and deploy programs into the robot. You can find all the details, plus the images you need to put into your PICO-W here.

Too much voltage is bad for you

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the first PICO powered Pixelbot

I’ve not made a brand-new Hull Pixelbot for a while. Today I made a new one which is powered by a Raspberry Pi PICO. I usually power the robot from four (or sometimes five) AA batteries. This gets me around 6 volts. I did that today with the new robot and it failed to work. It turns out that the Raspberry Pi doesn’t like voltages much higher than 6 volts, and shows its displeasure by not working. I had scrabble around to find a set of “slightly worn” batteries to get it going.

Slow baud rates and the Raspberry Pi Pico

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Hull University campus looking good

It’s strange the things you discover when you try to do something. Today it was all about slow baud rates.

What’s a baud rate? I hear you ask. Well, baud apparently stands for “binary asynchronous unit of data”. Or it’s an abbreviation for the name Emile Buadot who was a French pioneer of digital communication and had an amazing moustache and beard. Emile was sending text down a single wire and he was doing it one bit at a time. Assemble enough bits and you can match patterns of ons and offs to particular characters. The data stream would begin with a start bit (to tell the receiver that a character was coming) and then have a bunch of signal levels that represent the character being sent. One thing that was important is that the sender and the receiver needed to agree on the rate at which the data was sent. Otherwise things get garbled. So they invented the baud rate (number of bits per second) and created some standard speeds (110,300,600,1200, 2400, 9600, 115200 and so on…) Baud rates are still used today. The GPS receiver in your mobile phone will be sending position information into your phone processor via a serial data stream with a particular baud rate.

When I connect a Hull Pixelbot to a computer I have to set a baud rate for the serial connection. I use the horrendously slow “baud rate” of 1,200 bits per second. This is because the program that the robot receives is stored in EEPROM in the robot (EEPROM stands for “Electrically Erasable Programmable Read-Only Memory). This is so we can turn the robot off and it will still remember the program it has been given. EEPEOM is awesome, but it is also very slow to write. The hardware has to bash the bits into the hardware components in the memory device and this takes time. I could have added handshaking - where the robot sets a signal to tell the host computer to stop sending - but instead I did something quick and dirty, which was to slow down the robot baud rate to the point where the EEPROM could keep up.

This kludgy decision came back to haunt me today when I tried to use an Arduino programmed Raspberry Pi PICO at 1200 baud. The PICO seems to get upset when you try to talk to it via a serial port running at 1200 baud. Not sure why, but the result is that my robot code doesn’t work properly. Oh well. I’ll just have to speed up the serial port and add some handshaking. I believe this is called “paying off technical debt”….

Migrating Arduino C to PICO C

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Nothing to do with the subject of the post. Although the I guess you can see the “SEa”

You’d think it would be easy to move a C program from the Arduino platform to the Raspberry Pi PICO. After all, we have the wonderful libraries from Earle F. Philhower, III and the fabulous PlatformIO framework you can use to manage your project (don’t forget to perform this stuff before you try to build anything). And anyway, C is the same everywhere. Right?

Wrong.

When I write the Arduino stuff a while back I made one or two questionable design decisions. One of them was to use the char data type to hold 8 bit values. This was kind of OK back in the day (and by this I mean the 1980’s) but it turned out to be a stupid thing to do. Because some C compilers think that char holds a signed value (-128 to 127) and some think it holds unsigned (0 to 255). Of course the Arduino C compiler goes one way and the PICO C compiler goes the other way. Neither are wrong - the C language standard doesn’t specify this - and you could argue that anyone daft enough to perform maths with variables that are supposed to just hold character codes deserves all the trouble they get. But we are where we are, which in my case was looking at a program that has been working for years and has suddenly gone nuts.

I actually fixed it quite quickly once I figured out the stupid thing I’d done. The Pico debug probe proved very useful for this. I was able to set breakpoints in the timer interrupt handlers and then watch as various counters were updated. When I saw the code subtract 1 from 0 and get the answer 255 I knew exactly what had happened…..

Agile Octopus Tariff Display in HackSpace magazine

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I get my copies of the magazine from Readly

If you’re wondering what that distant rumbling noise is, it might be crowds of people rushing to the newsagents to buy their copy of HackSpace magazine so that they can read my article in it.

Or it might be a bus going past.

Anyhoo, the article is out there. You can find the project on GitHub here.

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They really knew how to make things back in the sixties

Started a new project today. I’m taking an old phone and making it more interesting. It’s going to have a Raspberry Pi inside along with extra circuitry to make the bell ring. Which is proving interesting. The bell in old phones is triggered by a 70 volt ac signal. Now, 70 volts is the far side of “tingly”. Anything below 50 volts is probably OK to grab hold of, but 70 could give you a shock you could do without. Especially at my age.

I’ve manged to get an inverter to convert 12 volts into a slightly less nerve jangling 35 volts or so. The plan is to drive the two coils that work the bell (you can just see them at the very top of the picture above) separately. So that I only use half the voltage. All I need is another MOSFET power driver (I’ve said this many times) so that I can control each coil individually. It should arrive tomorrow. I’ll add it to the circuit that I’ve already built which uses one MOSFET so that I can make the bell both “ding” and “dong”.

Agile Octopus Histograms

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This is a very nice lcd panel

I spent some time today working on my Agile Octopus price display. Agile Octopus is an electricity tariff where you get a different price every half-hour during the day. A while back I made a device that would get the current price and display it, but now I’ve added a little histogram that displays upcoming prices for the rest of the day. The picture above was taken at 7:14 pm. The solid lines in the histogram are the hours and the dotted lines the half hour prices. On the right you can see the minimum and maximum prices. It looks like the prices will be going down over the evening. We’ve found this quite useful when deciding when to put the washing on or bake a cake. The display is powered by a Raspberry Pi PICO-W driving a rather nice LCD panel from Pimoroni.

It’s actually rather pleasing to make something that folks actually find useful and might even save us money.

Radios in tins = bad idea

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Perhaps they might make a nice birthday present…

I’m making a new embedded device. It’s going to be a Bluetooth remote control. I’m on an upcycling kick at the moment, and in a tradition going back a while I thought I’d put the device in an Altoids tin. I bought the mints and then I realised that Bluetooth uses radio to work, and putting the PICO W in a metal box (i.e. Faraday cage) might not be for the best. Oh well.

Mdns makes your embedded devices easy to find

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I’m making a network controlled light. The idea is that the light hosts a web site which you can find with your phone or computer. The light will have an internet (IP) address which you can use to locate it on the network (something like 192.168.50.5) but this might change as these addresses are assigned by your network router on a first-come first-served basis. What you really want to be able to do is refer to your light as “flashlight.local”. The mdns service makes this possible.

I’m using Circuit Python to host the website in a Rasbperry Pi PICO-W. They have a lovely HTTP server library which works a treat. It also supports mdns (Multicast Domain Name Server). This lets applications (for example your browser) ask if anyone on the local network has a particular name (in this case flashlight.local). The mdns server running on the PICO-W responds to these requests with a network address which can then be used to contact the PICO-W. The code below was added to the application and starts the service running. This code is slightly different from the example code for the service, but it does work very well. 

import mdns


mdns_server = mdns.Server(wifi.radio)
mdns_server.hostname = "flashlight"

Once the server has been started it seems to just run in the background responding to requests.

This is the final website for the light

You can use this to make your embedded devices much easier to locate. If they get given a different IP address next time they start up they will just keep going.

Cockroach Circuits

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I’d say “don’t do this at home” but I’m doing it at my home so it must be OK…

I can just about fit a PICO inside my remote controlled flash light, but there is hardly any room for anything else. So I’m using the “dead cockroach” hardware construction style. The circuit looks like a dead cockroach with wires standing in for legs. The connections are created by soldered wire-wrap wire into the holes in the board. I’m going to wrap the whole thing in insulating tape before fitting it into the flash. I like using wire-wrap wire. It is so flexible that it doesn’t tend to come undone from connections. I’ve got lots of different colours, which makes it much easier to follow. The circuit above is an implementation of this:

My level converter is blue though…

The important thing to do is keep testing as you build it, although so far it has kept working .

Hurray for Level Converters

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At its brightest this pixel gives out 3 watts which is a lot of light

I’m working on my PICO controlled flashlight. Today it was time to wire up the output led. I’m using a Pixie light. This needs 5 volt levels to control it, but the PICO only produces 3.3 volts. This might just work (some things do) but I’m a bit concerned that if the power voltage for the lights gets a bit too high the light will not work or worse, be unreliable.

So I’m adding a level converter. These are very cheap and easy to buy (search for “arduino level shifter” on your favourite ecommerce site), but a bit of a pain to wire up as you have to connect input and output signals as well as power supplies and grounds for each side of the connection. However, as you can see above, the light works fine. Next I have to work out how to get the circuitry into the flash gun.

Remote Controlled Lights Working

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This is the prototype light display

I’ve got the code for the remote controlled flash light just about working. It turns out to be a fairly simple matter to get a web site host running on a PICO and then get it to respond to incoming requests.

This is the interface to set the colour of the lights

I’m waiting for my super-bright led to arrive and then I’ll get the hardware built. Great fun. I’ll put all the code and designs onto GitHub when its finished.

Fun with a Flash Gun

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Nothing like having an Auto Thyristor in your flash gun

We were out and about at Cottingham Day this weekend. I took loads of pictures using my Minox B on very old film. That didn’t end well. Which is why I have no pictures of the event at all.

While we were out I picked up this flash gun on a second hand stall. I fancied having another flash gun, particularly for two quid. Of course it doesn’t work. To be honest, I wasn’t expecting it to. These things don’t age particularly well and Cobra is not a name known for quality and longevity. In fact I until I found the flash gun I didn’t think it had anything to do with photography at all.

I’m not bothered though. I plan to take out the internals and replace them with a PICO-W to create a remote controlled light. I can use the battery compartment, reflector and even the flash zoom lens and my plan is to keep it looking as much like the original as possible.

The big grey thing is the capacitor. Need to be careful with that bit as it might have residual charge in it.

I’ve got the flashgun to pieces. Turned out to be quite easy. The main part is held together with little metal clips. The circuit boards are almost exactly the same size as PICO, which has got to mean something. Next step is to work out how to fit some lights inside.