diy | Code and Life

Visit to the Official Raspberry Pi Store in Cambridge

Two weeks ago I had the chance to visit the official Raspberry Pi store in Cambridge. Apart from those living in the UK, I think not many will it that far, so I thought to share my pictures from the visit for you to enjoy (and maybe evaluate whether it’s worth the trip). Enjoy!

The Store

The Raspberry Pi Store is located in the Grand Arcade shopping mall, and on the second floor. Looks nice and official.

Naturally, it houses an excellent selection of the Pi boards. There was 3B-, 3A2, Zero, Zero W, Zero W+, compute modules, Pi 4 of course (with different memory options), all with good availability. To cheapest Zero boards were limited to 1 per customer, much like in web store. All boards had a good choice of cases as well on sale. Very nice.

You could also get whole computer kits with a nice raspberry themed keyboard and mouse, as well as a case, an SD card, power delivery (UK plug at least on the display version) and a beginner’s guide. Nice combo, although it of course about doubles the price tag of just the unit itself.

The dual monitor capability of the Pi 4 was very much on display, and there were a couple of machines to try out in the central table area of the store. The machines also had network connection, which was nice for test drive purposes, and not something that even mainstream computer stores have.

And if you want to tout your inner pi’ness, there was of course coffee mugs, notepads and t-shirts available. Would definitely have gotten one if I drank coffee, or had arrived to UK with more than just carry-on luggage!

Cool things with the Pi

Another thing prominently shown at the store were all the projects that you could do with Raspberry Pi. Here is a setup with an ultrasound distance sensor wired to the board.

Apart from trendy slogans and on-display unit, it was more than just a show or a “hands off demo”. The machines usually had a Python editor open with a short piece of code showcasing the actual DIY setup on display, which you could run and try out — or even modify! This is something that many kids or programming newbies will hopefully find exciting and maybe inspire them to try it out themselves.

Here’s another one with a Sense HAT from element 14 on top a Pi unit. It had a nice RGB display with the code to run animations in, so I naturally had to take a shot and made an old-school “random red and green blinking lights” progression that you see happening in front of very old mainframes. Was a bit disheartened I could not get my own invented-on-the-spot random number generator working and had to resort to stanrdard Python RNG. :(

Another with basic GPIO demo with a button, and some leds. The exact setup was naturally available for purchase on the shelves. The “project stands” usually also had a small display telling a bit more about what the setup is doing.

For those with less programming ability or maybe familiarity with the visual programming language used in LEGO robotic projects, there was also a Scratch demo in the store.

The Pi Accessories

In addition to the Pi boards, there was a multitude of exciting components and project kits, including but not limited to robotics, OLED and TFT displays, all kinds of Pi sensor hats, basic electronics kits, and sensors. The pricing was also good, and competitive with web, especially with no shipping fees and zero wait time. I spent probably an hour poring through the shelves and trying to decide what to pick!

Particularly tempting were the colorful Picade units on display, with robust controls and great retro feel. The size and price thankfully saved me from hauling these units back to Finland, but it was not an easy temptation to avoid!

There was also a very interesting mechanical “Turing Tumble” kit on display. It’s basically a mechanical “computer” powered by marbles. You can take a look at their website to learn more. Different mechanisms enable simple logic to be built, and even though the space is too limited to make a 16-bit adder or anything of the like, you’ll certainly have fun grasping the fundamentals!

Pi literature

In addition to coffee mugs, you can see a couple of t-shirts that were also available. There were also good hacker and geek friendly magazines with reasonable pricing, definitely something that you might pick up to spend some time with on the train ride back to London for example.

In addition to magazines, there was an excellent array of Pi and programming related books. Had I not switched solely to ebooks myself (and not having read those “Learn C” books already 25 years ago) I’d definitely left the store weighed down with some quality reading material!

Great selection of Raspberry Pi books catering all topics from computer architecture to projects and kids was superb as well. If you’d want to gift your kid, relative or neighbor (or even a co-worker) some Pi knowledge, you’d be well covered here.

All good things must come to an end

After much deliberation, I finally picked some stuff and headed to the counter. And what a counter! Behind the glass there seems to be every model of the Pi produced, as well as some pure boards and probably a couple of prototype ones as well. A mini-museum in itself!

My official Raspberry Pi Store receipt. Yeah I know: A measly Pi4 case! What was I thinking?! Probably mostly the 25+ boards, sensors, cases and other stuff waiting at home for me to work on — while walking the aisles I realized that apart from the Picade and the robotics units, I pretty much had almost every kind of gadget already purchased. So I settled for something light but officially Pi.

I had a superb visit, and considering the great historical landmarks and good pubs and restaurants, I can warmly recommend a trip to Cambridge and the Grand Arcade Pi Store to anyone visiting UK for more than a day or two.

In addition to housing an excellent selection of all things Pi, the official store gets my respect for representing Pi culture and projects in a very easy to approach and inviting manner. I believe the foundation’s goal to bring children to computing is well served with the store, and hopefully they can open a few more to other cities as well. The concept certainly seems strong enough. Five stars out of five.

Power up your computer wirelessly with Wemos D1 mini

Tired of reaching for that power button? Or perhaps you’d like to be able to turn on your PC when travelling? I sometimes like to do that to access some local files (or software via VNC), but dislike leaving the PC on for days “just in case”. This article explains how you can do it with the $3.50 Wemos D1 mini.

Wake-on-LAN is of course a great idea, but it only works if your PC is physically wired to the router. Wake-on-WLAN theoretically should work for WLAN as well, but here’s a shocking revelation: it usually does not, as it requires your PC to power up your WLAN card for it to receive the magic WLAN packet, and router support. At least I’ve never had a combination of network card and router that would work.

I used to have a nice DIY knock-sensor to PS/2 thingy, but the piezo kept dropping out, and got tired of repeating the required sequence of knocks. So I thought it would be cooler to have just a Bluetooth button I could use to do the same. I had a WLAN enabled Wemos D1 mini board lying around, and it only draws less than 100 mA of power, so I thought to find out if I could make it listen to a “magic packet” and boot up my PC. Turns out it was easier than I even thought!

Note that this project involves opening your PC case and playing around with your motherboard power switch wiring. Everything should be relatively hard to screw up, but if done wrong, you may get electrocuted, you may stick a screwdriver where it shouldn’t go and damage your motherboard or other components, so proceed with your own risk!
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DIY Bluetooth Keyboard Breakout for $10

You could get an excellent Bluetooth keyboard controller from Adafruit called Bluefruit EZ-Key which allowed super easy creation of projects that sent keyboard presses (for example a gamepad) just by connecting some switches to the pins. However, the EZ-Key cost $20 and is now discontinued. And in any case, Bluetooth-capable devboards are now available from AliExpress for a few dollars, so $20 today feels on the steep side. “Could it be done cheaper?” I wondered…

I have honestly about a dozen cheap wireless devboards lying around, many based on ESP8266 which only have Wi-Fi, but some also with ESP32 which includes Bluetooth. I spent some time trying to configure a Chinese ZS-040 serial Bluetooth module to function as a keyboard, but the AT command set was a very small subset of what the similar HC-05 / HC-06 modules have. After an evening of trying, I decided to give up on that. There are instructions how to flash HC-05 modules with RN-42 firmware to get Bluetooth HID capability, but it will require quite a few steps.

I also took a look at esp32_mouse_keyboard project, but for some reason or another, abandoned that avenue. Don’t recall if there were obstacles or the project was still incomplete a year ago, might also be that the ESP32 only had BT LE which technically didn’t support HID (Human Interface Device). Throw me a comment if you have that working!

Meanwhile, another idea dawned to me:

A Cheap Bluetooth Keyboard Must Contain A Bluetooth Module

Enter the wonders of AliExpress: While you cannot source an easy BT keyboard module from US under $20, you can get a full mini Bluetooth keyboard for $9.50 (at time of writing) including postage! This package ought to contain:

A fully compliant Bluetooth board that pairs with iOS, Android and PC devices
Full functioning keyboard and case
Presumably, a battery and a way to charge it

Sounds a too good deal to be true? Well, let’s find out! The keyboard has a solid metal backplate that is easily screwed open with micro cross head screwdriver. Once inside, it reveals a very professional layout with a flat ribbon cable (or “FCC cable”) coming from the mechanical part into the controller module, And a small (most likely LiPo) battery.

Taking the tape off and turning the board around reveals a bit spacious, but very professional looking PCB with clear markings. There are easily usable on/off switch and connect button on the PCB, a connector for the keyboard switches, and obviously some kind of microcontroller wired to the connector, as well as another smaller chip that is most likely a voltage regulator or charging chip.

I Googled around to find out if the “YC1026” MCU would have a datasheet to help me along the way, but unfortunately I only got Chinese web pages (most likely the manufacturer) without any documentation. Time to dig out my trusty Picotech 2000 scope and do some old-fashioned reverse engineering!
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Simple X Audio Switch (Double-Y)

I’ve had a small problem over a year: I have two headphone amplifiers, a transistor-based O2 headphone amp, and a tube-based Little Dot MKII. I also have two sets of headsets. Because switching the cables all the time is somewhat tedious, I haven’t really used the other amp and headphone set.

There are several Y switches that you can buy, but most seemed either expensive or mostly tailored towards electric guitar enthusiasts. And I would still need to combine two Y switches to toggle between the two amps and headphones. As the construction is really simple, I decided to solder my own. Here’s a short tutorial on how to make one yourself. You’ll need:

4 audio connectors (I chose 3.5mm over RCA), two to each end
2 switches with at least 3 connectors (left, right, ground) – I chose two 4 way switches
A box where you can drill holes for the connectors and switches
Small length of wire, some solder and soldering iron

1. The Schematic

The design of the switch is extremely simple. In both ends, three wires come from each of the two connectors to a switch, and the switches are connected to each other. I chose not to combine any ground lines to avoid ground loops. You need also to select a switch which breaks the connection on one side before connecting the other so the amplifiers will not feed into each other.

2. Soldering the wires

Despite the simple construction, there is a lot of soldering involved. Each of the four connectors will have ground plus left and right channels, and all have the switch on the other end. That makes 24 solder points (4x3x2), and there’s six more between the switches for a total of 30 points. The 3.5mm connectors had small “L” and “R” markings to tell which channel is left and which is right. I used different colors of wires for each type to avoid mixing L, R and ground.

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Turning PC On with a Knock Using ATtiny45 and a Piezoelectric Sensor

Today’s post is something I’ve prepared for a long time. Hardware-wise it’s a simple thing – ATtiny45 emulating a PS/2 device, sending a keypress when three knocks are detected in the attached piezoelectric sensor (or piezo buzzer as they are also called). But if your computer can boot on PS/2 keyboard input and you have your computer stowed somewhere hard to reach (or just want to impress your friends), it’s a pretty neat little gadget! Here’s a video of it in action:

My PC takes a few seconds to put anything on display, but if you look at the bottom right corner, you can see the blue power LEDs light up immediately after the knocks.

What You’ll Need

Hardware-wise this hack is super simple. You’ll need less than $10 in parts and many probably already have these lying around:

ATtiny45. Actually, any ATtiny or ATmega with 4kB or more flash, A/D converter and two timers will work with small adjustments, and with -Os -DMINIMAL compiler flags also 2kB MCUs (ATtiny2313 doesn’t have a A/D but you can either work around it or use a button)
Piezo buzzer and 1 Mohm resistor to act as knock sensor
PS/2 connector, or alternatively a passive USB-PS/2 adapter (I have half a dozen from old keyboards and mice) and USB cable (like the one I used in my V-USB tutorial)
Breadboard and wire. Alternatively you can solder it on a simple PCB like I eventually did.
Optionally, a 4k7 ohm pullup resistor for RESET line, and a LED and 330 ohm resistor to indicate state

The Schematic and Breadboard Setup

The PS/2 part as discussed in my minimal PS/2 keyboard post doesn’t require any other hardware than the ATtiny. The piezo element uses a 1 Mohm resistor like in the Arduino Knock Sensor tutorial, providing a path for voltage level to get back to zero over time. The LED is connected to PB4.

The PS/2 connector also provides power to the device. Instead of soldering a custom PS/2 connector for the project, I took a passive USB-PS/2 adapter I had lying around and used a multimeter to find out which USB pins correspond to the PS/2 ones. Not surprisingly, PS/2 GND and VCC are connected to USB GND and VCC. In my adapters, PS/2 clock was connected to D+ and data to D-. You can see the mnemonic printout I made on that one below, as well as one possible breadboard configuration.
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DIY ATtiny45/85 ISP Header

A quick weekend tip for a change, I thought to share a nice small soldering project will make programming ATtiny45 and ATtiny85-based projects a flash:

Basically I took a piece of veroboard, soldered some extra long pin headers on the bottom so it will form a tent of sorts above a ATtiny45/85 attached to a breadboard project. Then I soldered a 6-pin header to attach the ISP programming cable to, and used short pieces of jumper wire to route the header pins to correct ATtiny85 pins.

Now whenever I need to flash a ATtiny45/85 project sitting on a breadboard, I can just put this on top of that and never need to look up the pin layout again!

You can click the images for larger versions. I’ve also been quite busy with my PS/2 projects, so I have some nice material to share regarding that when I have some free time again in my hands!

DIY USB password generator

Having done half a dozen V-USB tutorials I decided it’s time to whip up something cool. As USB keyboards were an area untouched, I decided to make a small USB HID keyboard device that types a password stored in EEPROM every time it’s attached. A new password can be generated just by tabbing CAPS LOCK a few times (4 times to start password regeneration and one tab for each password character generated, 10 is the default password length). Below you can see the device in action:

The place I work at requires me to change my password every few months so this would be one way to skip remembering a new password altogether (as long as I remember to write it down before regenerating a new one so password can be changed :).

What is inside?

The device is powered with a simplified version of the hardware I used in my ATtiny85 USB tutorial – I stripped away the LCD, reset pullup and both capacitors. If you’re better in cramming components inside enclosures I suggest adding at least a 0.1 uF capacitor between VCC and GND, but it seems to work fine even without it:

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