I love watching ideas bounce back and forward between people on Twitter and see them grow. The best for me recently started when The Verge posted a story about an OpenSource Android App which basically turned a Wii Balance Board into a Withings weighing scales, including RunKeeper and Fitbit integration. I retweeted it and it was picked up by Joe Desbonnet. He realised you could also do some interesting things with the Balance Board and a Raspberry Pi and started hacking. Which of course made me realise I could control the i-racer with it!
Here’s a wee video of it in action:
Apologies for the mobile interference in the audio. I was using my new SGS4 to SSH to the Raspberry Pi to kick off the Python code. The ConnectBot guys really need to fix the microscopic font on screens like the SGS4!
The car isn’t very fast in the video as the Lego added a lot of weight and I hardcoded the speed to 50%. We’ll try again next weekend using a lighter shell, full speed and tarmac instead of cobblelock.
Technical Nitty Gritty (not too Gritty!)
My initial experiments with the Balance Board did not go well. Eventually I discovered that the version of the cwiid Wii library that is available on Raspberry Pi (and Ubuntu etc) is not able to deal with the Balance Board. See this bug. I applied the patch and re-built my own deb files. To use them, just unzip them on the raspberry pi and install like so:
The rest of the time was just spent tweaking the numbers so that I could interpret someone leaning in various directions irrespective of their weight. It’s still not great but works for me, a 7yo and a 6yo.
All the old i-racer Bluetooth code carried over unchanged from our Cheese Controlled Car. Follow the instructions there for installing various Bluetooth bits and bobs on the Raspberry Pi.
I was very surprised that I could talk to both the i-racer and the Balance Board over the same $2 Bluetooth adapter. I was sure I’d end up having to use two adapters.
You can, as ever, grab the code from Github. The only changes you need to make in the code are to set the Bluetooth MAC addresses of both the Balance Board and the i-racer.
Sidenote: The Android App was a dead end. It doesn’t work on Android 4.2 because Google decided to upgrade their broken Bluetooth stack and actually managed to make it worse.
Any questions, leave a comment.
Only if you really need it: Building those cwiid libraries yourself
sudo nano /etc/apt/sources.list
Add the following line:
deb-src http://archive.raspbian.org/raspbian wheezy main contrib non-free rpi
Then do the following:
mkdir ~/build
cd build
apt-get source python-cwiid
apt-get build-dep python-cwiid
cd cwiid-0.6.00+svn201/
Then edit these three files and add the changes from https://launchpadlibrarian.net/115501163/balanceboard.patch (or run “patch” if you are familiar with that)
We have a treadmill setup in our house which has always faced some sort of media centre setup. It’s the only way I don’t lose my mind with boredom when running during Irish bad weather (August to June). Originally it was an XBOX-1 with XBMC on a 14″ Philips portable CRT. Then it became a Patriot PBO connected with a HDMI-VGA adapter to an LCD monitor and now it’s a Raspberry Pi running Raspbmc connected to the same monitor.
The problem in all these setups has been audio volume. When I’m pounding my featherlight torso on the treadmill deck, I need lots and lots of volume to hear anything. I bought a 2.1 Speaker thingy from Lidl a good while back and that helped but it still wasn’t loud enough on some media.
Then I got a Fiio E3 battery-powered headphone amp and that worked well with the PBO. The big downside was that it chewed through the single AAA battery in no time at all and was unusable with rechargeables.
I came up with a really cool solution to the battery problem. I got one of these adjustable voltage regulators from DX, cut the head off an old Nokia charger and wired it in. Then I used a multimeter on the output and twisted the potentiometer until I got 1.5V out. I used crocodile clips to then connect to the Fiio.
I can’t recommend that voltage regulator highly enough. If you, like me, have tons of old power supplies from long dead electronics, it can scale down anything to the voltage you need. I’m getting another one to power the Raspberry Pi from an old Linksys 12V wall-wart as most of my phone chargers simply don’t have enough juice. At €2.90, it’s super value.
The problem with the PBO as a media player is that its UI is garbage. It feels like something from the 90s. In particular, it’s missing a simple but crucial feature we love in XBMC – a tick mark to show you’ve already finished watching something or you are mid-watch. The PBO is also terribly crashy and struggles regularly with SMB network shares.
So we finally moved to Raspbmc and it works really well. Well almost. The only big problem is the analogue audio, it has no amplification on it at all. So even with the Fiio and the Lidl speakers up full, it is very hard to hear on the treadmill.
I had a go with using a USB audio adapter but that was a disaster. Audio out of sync and the GUI mis-behaved the whole time. It was louder tho!
Then I went looking for something with more welly than the Fiio. That company has other devices but they are even more expensive than the RPi itself.
But after much gnashing of teeth with no output and then mono output, I realised that a loudspeaker amp is totally different to an inline headphone amp and just cannot work in that configuration. So much for 6 years of Electronics in UCD
Weirdly I could only find loudspeaker amps on DX, eBay and Amazon. A bunch more googling and reading on audio/hifi/hobbyist sites and fiiiiiinally I found a headphone amp design called the CMoy which (a) looked easy to make (b) looked cheap to make and (c) had very detailed instructions for idiots like me.
I ordered the various bits online from the usual suspects (eBay, DX, Farnell) and put it together last week on a mini-breadboard. Shockingly for me, it worked first time! The only difficulty in the instructions is that they are customised for a very specific Radioshack board and I had to translate that to my simple breadboard.
Then yesterday I sat down to build the final circuit on some stripboard I got yonks ago in Maplin. I’ll be honest, it took a while. Particularly translating the layout to a very small bit of board. But yet again, magically, it worked first time. I have it powered with another old Netgear 12V wall-wart. It’ll take anything from around 9V to around 30V which is really handy.
A bit of glue-gunning on to the unused lid of a Raspberry Pi case and I have a finished product. And boy is it loud! We’ll need to be careful we don’t blow the amp inside the Lidl speakers or damage the speakers themselves. Mrs D’Wife, who ran 10 miles on the treadmill today (10 miles!), approves of the improved volume level too.
I highly recommend the CMoy kit if you are struggling with audio volume levels on anything, not just the RPi. At some point I’ll draw out my layout to save others the hassle of figuring out the original layout. Hit me with any questions below.
UPDATE 1: I completely forgot to do a costing on this. Whilst the overall spend for me was €32.45 (incl P&P), this includes some giant packs of resistors, capacitors and LEDs that I have been using on multiple projects. If you can manage to get exactly the amount of each thing you need, then the entire amplifier only costs €6.59. That’s obviously excluding the power supply, solder, tools and the glue from the glue gun. You will find it difficult to just buy 1′s and 2′s of things. You can do it in Maplin but it’ll cost you a lot more. You can also do it on sites like Farnell but they have a minimum order of €20.
So either buy the bigger packs on the basis that you’ll be making other things or do it as part of something like a Coder Dojo where lots of you pitch in together to make lots of these.
After the enormous attention that the Cheese Controlled Car got, my thoughts moved to what else we could use with the i-racer. Two immediately came to mind: the Wiimote and a mousepad. But both went in directions I didn’t expect. I’ll write up the mousepad at a later stage but this post is about the Wii.
The Wiimote is an amazing device. I don’t think the average person realises that it has a VGA infrared camera at the front, has a bunch of accelerometers inside and communicates with the Wii using Bluetooth.
The bit I didn’t know until recently was that it also talks to the Nunchuck using I2C (I squared C, not I two C). This is a brilliant low-level communications protocol invented by Philips many years ago to make it very easy for inter-IC communication using just two wires. I spent a lot of the 1990s writing and debugging I2C drivers.
This made me realise I could dump the full Wiimote and just use a Nunchuck. Both Raspberry Pi and Arduino support I2C and there is tons of code on the web for both platforms.
TL;DR – If you want to jump straight to the outcome, here’s a really rough video of it in action:
Whilst there are adapters out there to get at the Nunchuck’s pins, I decided to just cut the cable and go direct. A lot of our Nunchucks have rusty connectors due to the kids blowing on them to get a “better” connection. So they are basically spittle-filled. Gross I know.
A few minutes of soldering and I had the Arduino happily reading the joystick, buttons and accelerometer of the Nunchuck. But then I sussed that the simple serial Bluetooth dongle I had bought on DX to talk to the i-racer was Slave-mode only (HC-06) whereas I needed the more expensive Master-Slave one (HC-05). I managed to find the right one on Elec Freaks.
Using Raspberry Pi and Python
Whilst I waited for that to arrive, I decided to return to the Raspberry Pi and use that. Its I2C interface is available on some of the external PINs as follows:
Pi pin 1 is 3.3V and connects to the Nunchuck Red Wire
Pi pin 6 is Ground and connects to the White wire
Pi pin 3 is the I2C Data Line and connects to the Green wire
Pi pin 5 is the I2C Clock Line and connects to the Yellow wire
Then you need to do some simple installs on the Raspberry Pi to enable I2C and access it with Python:
Byte Description Values of sample Nunchuk
1 X-axis value of the analog stick Min(Full Left):0x1E / Medium(Center):0x7E / Max(Full Right):0xE1
2 Y-axis value of the analog stick Min(Full Down):0x1D / Medium(Center):0x7B / Max(Full Right):0xDF
3 X-axis acceleration value Min(at 1G):0x48 / Medium(at 1G):0x7D / Max(at 1G):0xB0
4 Y-axis acceleration value Min(at 1G):0x46 / Medium(at 1G):0x7A / Max(at 1G):0xAF
5 Z-axis acceleration value Min(at 1G):0x4A / Medium(at 1G):0x7E / Max(at 1G):0xB1
6 Button state (Bits 0/1) / acceleration LSB Bit 0: "Z"-Button (0 = pressed, 1 = released) / Bit 1: "C" button (0 = pressed, 1 = released) / Bits 2-3: X acceleration LSB / Bits 4-5: Y acceleration LSB / Bits 6-7: Z acceleration LSB
However, despite multiple attempts, I haven’t been able to read reliably from the Nunchuck on the Raspberry Pi. An appreciable percentage of the data comes back as 0xFF. I have no idea if it’s the wiring, the RPi CPU, the I2C driver in Linux, the I2C library in Python, timing or the code above. I don’t believe the problem is the Nunchuck as I now have it working 100% reliably on the Arduino. In any case, the RPi was only ever going to be the proof of concept platform as we obviously need something more portable and less power hungry if we are going to chase a remote control car around the house.
Using Arduino and HC-05
Last week the HC-05 module finally arrived from China and I was able to start playing with it on an itty bitty Arduino Nano yesterday. Using the basic instructions and code from here, after a lot of misunderstanding what pin did what, I was able to connect to the HC-05 and it was able to connect over Bluetooth to the i-racer.
I pulled in the Arduino Nunchuck code from here and converted my Raspberry Pi Python to Arduino Processing (basically a C variant). My code maps the wide range of movement in the Nunchuck joystick to the basic 6 degrees of freedom plus speed on the i-racer. It took quite a few hours of Googling before I finally sussed that “arccos” was the mathematical function I needed. So the code splits 360 degrees into 6 segments of 60 degrees. That gives us Stop/Right Forward/Forward/Left Forward/Left Backwards/Backwards/Right Backwards. Speed ranges from 0 to 15.
It was a real delight to see the i-racer responding with no delay to my thumb movements but the code definitely needs tuning and I’m pretty sure the Nunchuck is not giving a full range of motion. It’s pretty ancient and so hard-left does not give the same value as hard-right for example.
Fionn was thrilled as I’ve been promising him I’d get it working for the past month! Interestingly, his first instinct was to use the accelerometer in the Nunchuck instead of the joystick. This must be how most Wii games work. It shouldn’t be too hard to switch the code over to using the accelerometer but we’ll use this for a while.
After a few more goes, both Fionn and Oisín pointed out that their natural action was to move the joystick in the direction they wanted the car to go, relative to them. I think I’ll leave that for another day
Being able to run the whole thing off 4 rechargeable AA batteries is a real plus. I’m also a huge fan of the Shrimping It project which is a minimalist Arduino setup using little more than the ATMega itself. I have two and the idea is to replace the Arduino Nano with one and make the whole thing even smaller again. The i-racer runs out of juice way faster than the remote ever will so I may be able to try AAA rechargeables or maybe a little Lipo battery.
Next up is probably a left-over Nintendo DS touch-screen as the controller. I also think we’ll start adding “headlights” and an ultrasonic detector for collision avoidance. These will require changes to the i-racer firmware itself so you’ll probably hear from me again in 2017!
I’ve been lucky to-date that I haven’t killed the RPi stone dead with my little projects. I find the simplest way to help avoid any catastrophic shorts is to use an old 40-core IDE cable (note, the “newer” 80-core ones don’t work even tho they fit). I Dremeled mine last week to fit in this very nice inexpensive case.
In many ways, that GPIO header on the RPi is like the expansion port on the ZX Spectrum. So much possibility, so much danger
I’m finding myself jumping back and forth between the RPi and Arduino a lot recently. Arduino is amazing because of the huge body of code and boards that are available. Interfacing to most things often just requires wiring it straight in and pasting some code off the web. In the picture above you can see an Arduino Nano which is both tiny and cheap ($10). Where Arduino falls down is when complexity is required. A 8-bit CPU can’t just be connected straight to the internet or to a Bluetooth USB dongle. This means that some of the add-on boards (particularly Wifi) cost multiples of the Arduino itself.
The Arduino code for Nunchuck worked perfectly first time, but right now I’m waiting on a Bluetooth Master module from China to connect it to the i-Racer ($10 module vs $2 USB BT dongle). Whilst I’m waiting, I’ve been trying to get the Nunchuck working on the Raspberry Pi. I’ll do a full post in a few weeks but suffice to say it has not been straightforward. Scanning I2C reliably with Python is proving a struggle and I don’t know if it’s HW or SW related. Having a Python runtime and Linux kernel between your code and the Nunchuck may not be the best for realtime performance. Compare that to the Arduino code which is raw machine code with no OS, reading its pins directly on a bullet-proof I2C bus.
There are many types of boards out there to make interfacing to the Raspberry Pi easier. They range from simple breakout boards converting male headers to female headers all the way up to big motor control boards with their own microcontrollers. I haven’t bought any of these yet, so it’s up to you to figure out what is most appropriate for your project.
Slice of Pi
Only £3.90, this is a breakout board which just makes it easier to connect jumper wires and less likely that you’ll short anything out. One of its headers is XBee compatible. Probably worth getting no matter what you are doing. Very simple self-soldering to assemble and comes with all the parts
UPDATE 1 – 16/02/2013: Slice of Pi/O
Big thanks to Conor Houghton for pointing out this board which I had missed. It is the Slice of Pi with an IO expander chip. The basic idea is that you communicate to the chip using I2C and it handles all the actual interfacing and buffering. So your RPi is much less likely to be damaged. If you damage the MCP23017 chip itself, you just pop it out and put in a new one for €1.53 from Farnell. Lots of info about it here. This is in fact the board that I ended up buying. It is only £7.89 delivered to Ireland which is in keeping with the low price point of the RPi itself.
PiCrust
This is similar to the basic Slice of Pi but has more headers. However you have to order all the parts separately yourself. Still very inexpensive.
Adafruit Prototyping Plate
This is the same idea again but with lots of connectors and plenty of space to permanently solder things on. $16 in US and I’m sure someone is selling on this side of the pond too.
PiFace
This is more complex and has relays, motor control, switches etc. At €25 it won’t break the bank and comes fully assembled. You can program in Python, C and Scratch. The last one is verrrrry interesting for something like Coder Dojos. I showed my RPi at Bandon Coder Dojo last week and got a ton of interest from kids and parents. Being able to do robotics in Scratch would blow a lot of their minds.
UPDATE 2 – 17/02/2013: RaspiRobot Board
This was just announced by Sparkfun on Friday. It’s specifically for robotics and seems decent value at $29.95. After you’ve assembled it, it provides dual bi-directional motor controllers, two open collector outputs, two switch inputs and a voltage regulator capable of powering the Pi itself. A LiPo battery or 6 x AA batteries should provide the juice you need. Obviously Model A is the one to go with for robotics due to the much reduced power consumption.
Arduino Shield Bridge
This is a neat idea. It makes it possible to connect Arduino Shields (shields are the Arduino add-on boards) to your Raspberry Pi. Whilst boards like Wifi are expensive on Arduino, there are tons of control and interfacing boards which are very cheap. Things like Joystick boards, environmental sensors, heavy-duty motor control, RFID, XBee etc. They have created an Arduino-compatible library so you can use some of the same Wiring code on the Raspberry Pi that you would use on Arduino. Note that this can’t work with everything but their site is good in explaining what will work. It is €40 which is starting to get pricey for something which may only be suitable in a subset of cases.
Alamode
This takes the same Arduino idea and extends it further by basically giving you a full Arduino board which plugs neatly into the Raspberry Pi. You can see it as either adding Arduino functionality to the RPi or giving the Arduino very inexpensive Ethernet capabilities. However at $50, we are now at twice the price of a Model-A Raspberry Pi and many Arduino boards. So you really need to be sure this is something you need and will use. I’ve hooked Arudino up to RPi but only using USB. Clunkier, simpler but a lot cheaper.
Gertboard
This is probably the best known board as it was designed by one of the people originally involved in the RPi design. Whilst it is not “the official board”, many people see it as such. It is a very high end board with lots of functionality, particularly around motor control for robotics etc. It even includes the same ATMega MCU as an Arduino. Originally a kit, you can now buy pre-assembled for £30. My guess is that it will see the most community support due to its high profile. But like so many of the other boards I’d point to the fact that it’s more expensive than the RPi itself.
If I’ve missed any others, please let me know in the comments. At the minute I’m tending towards the simpler breakout boards. With a little care, you should be ok and they aren’t adding much to the overall cost of the RPi. The power requirements of the Pi mean that using it for robotics etc probably isn’t a runner for me and I’ll stick with the Arduino for that. Ditto anything that I want to do outdoors. But for projects where you need to get the data online, an RPi is ideal.
I’m particularly excited by the idea of using Scratch to both interface to the real world and maybe even access the web. I wonder is anyone working on web services functionality for Scratch? I was disappointed that no-one did the same for MIT App Inventor and the IOIO board.
Actually, that reminds me I meant to blog about ModKit. An absolutely brilliant Arduino project to bring Scratch-style/App-Inventor-Style development to that platform.
You install a simple program on your PC and then do everything else in the browser (desktop app optional). It’s amazing to drag a few blocks in a browser IDE which say “blink LED” and then the LED on the Arduino on your desk starts blinking! It’s projects like this that will get kids interested in hardware and electronics big time. Perhaps it might eventually support RPi plus one of the boards above.
When Santa told me that he was getting an i-Racer remote controlled car for Fionn, I was very excited. This is a remote controlled car that, on the surface looks very crude. Heck it doesn’t even come with a remote control.
That’s because it’s Bluetooth-controlled! You can install a simple Android App, pair with the car and control it either with on-screen controls or using the accelerometer in the phone.
As a standalone present it is pretty neat but like all remote controlled toys, I’m sure would be discarded after a few days use. However Santa didn’t want to spend a fortune on a full-blown Arduino-based robot platform or an even bigger fortune on Lego Mindstorms.
It’s when you start thinking about what is possible over time with the i-Racer that things get really interesting. Forgetting electronics for a minute, you could have huge fun making new shells for it out of different materials. Imagine a Foldify template for it so you could make printed paper shells. Lego might be a bit heavy but K’Nex plus some Sugru could work very nicely. Or what about bamboo food skewers or ice-pop sticks? Maybe just some stickers.
Then there is the code running on the car. The source is available so you can play around with it. Now this isn’t the easiest thing in the world to do since the car is not Arduino so you need compilers and special programming dongles, but the option is there.
Taking that one step further, you could clip on other bits of electronics. I have a temp sensor, a PIR detector and an Ultrasonic distance detector all winging their way from China. You could use these to give the car a lot more “intelligence”. There is also someone working on porting the car’s code to Arduino since the microcontroller is compatible.
But that stuff is hard and more long term and wouldn’t actually involved Fionn doing much. Always have to keep your focus on the “customer”! So I thought about it some more and realised that you could have enormous fun with how you control the car. The use of Bluetooth gives you a giant range of pretty *cough* easy possibilities.
So I started playing with some Python code and after a ton of dead-ends, Linux bugs and system problems I was finally able to talk to the car from my Ubuntu PC with a $2 Bluetooth dongle. (Details below)
Then I realised that this would be no use over Christmas as we spend it travelling to family houses around the country without the Ubuntu PC. My Windows laptop should work with tweaks but that’s not for games! So I started looking at the Raspberry Pi. Whatever problems I had run into on my PC were 10x worse on the Pi. (More details below)
After a ton of messing I got keyboard control working the way I wanted over USB on the RPi. Which leads to the piece de resistance – MaKey MaKey control. MaKey MaKey is a beautifully simple idea. It’s an Arduino-compatible board you plug into a PC and it emulates various key-presses and mouse clicks. You then connect whatever you want, as long as it is vaguely conductive, and use that for input. It famously uses bananas, pencil drawings and buckets of water as inputs to various fun software.
The Cheese Controlled Car (CCC)
So Fionn finally had the ultimate car controller. 5 Pieces of Christmas Cheese connected to a Raspberry Pi via MaKey MaKey talking to a car over Bluetooth. Check it out in action:
If you want to try this yourself and run into any problems, pop a comment in below.
Other possibilities include grapes (GCC):
And Barbie (BCC):
Now for the nasty details. Whilst these steps are quite short and the code is very simple, it took a week of evenings cursing, hacking and googling to get everything working right.
Figure out how to connect to car over Bluetooth using Python with PyBluez
Sort out bad bug in Bluetooth on Debian (and therefore Ubuntu)
Realise that most cheap micro Bluetooth dongles from China have duplicate MAC addresses and cannot talk to each other.
Discover that Bluetooth dongle works on USB hub on Raspberry Pi at low-level but Bluetooth stack cannot see it. So connect it to one of USB ports on Raspberry Pi
Discover that cheap Chinese Bluetooth dongles hang the Raspberry Pi after random amount of time
Switch to using older bigger more expensive Bluetooth dongle
Realise that Bluetooth dongle must be plugged in after booting Raspberry Pi in order for it to be detected
Repeatedly curse the totally messed up implementation of USB on the Raspberry Pi
Use a powered USB Hub to connect the MaKey MaKey and anything else like WiFi to the Raspberry Pi
Figure out basic keyboard reading in Python
Figure out reading keyboard in Python without carriage-return
Try PyGame for keyboard reading but discover it needs a screen attached
Figure out reading directly from USB with auto-repeat using Evdev and python-evdev (must be run as sudo)
Now you need to work around a nasty bug in Debian and Ubuntu. They have accidentally compiled in code for Nokia Series 60!
sudo nano /etc/bluetooth/main.conf
add this line to it:
DisablePlugins = pnat
Now plug in the Bluetooth dongle, power up the i-racer and run:
hcitool dev
It should detect your dongle and report its MAC address. If it does, then run:
hcitool scan
This should find the i-racer as a Dagu Car. Note its MAC address and then pair to it by running:
bluez-simple-agent hci0 00:12:05:09:94:26
where you replace 00:12:05:09:94:26 with the MAC address of your car. The PIN is either 1234 or 0000
In a Python shell, (sudo python) run the following to find out your Keyboard or MakeyMakey ID:
from evdev import InputDevice, list_devices
devices = map(InputDevice, list_devices())
for dev in devices:
print( '%-20s %-32s %s' % (dev.fn, dev.name, dev.phys) )
My MaKey MaKey comes up (with KB/Mouse/Joystick disconnected) as:
/dev/input/event0 Unknown USB IO Board usb-bcm2708_usb-1.3.3/input2
The Code
Finally run this code as sudo to control the car using the MaKey MaKey:
import sys
import select
import tty
import termios
import bluetooth
import time
from evdev import InputDevice, categorize, ecodes
if __name__ == '__main__':
dev = InputDevice('/dev/input/event0')
bd_addr = "00:12:05:09:94:26"
port = 1
sock = bluetooth.BluetoothSocket( bluetooth.RFCOMM )
sock.connect((bd_addr, port))
for event in dev.read_loop():
if event.type == ecodes.EV_KEY:
key_pressed = str(categorize(event))
if 'KEY_LEFT' in key_pressed:
# 0x5X for left forward. 0x51 very slow. 0x5F fastest
sock.send('\x5A')
if 'KEY_RIGHT' in key_pressed:
# 0x6X for right forward. 0x11 very slow. 0x1F fastest
sock.send('\x6A')
if 'KEY_DOWN' in key_pressed:
# 0x2X for straight backward. 0x21 very slow. 0x2F fastest
sock.send('\x2A')
if 'KEY_UP' in key_pressed:
# 0x1X for straight forward. 0x11 very slow. 0x1F fastest
sock.send('\x1A')
if 'KEY_SPACE' in key_pressed:
#stop
sock.send('\x00')
Note that this is extremely simple control with fixed speed just to prove the idea works. Real code will go up on GitHub when it has much more usable controls with automatic acceleration/deceleration etc and after I make it configurable with any i-Racer and with the MaKey MaKey on any USB port.
What’s next?
Apart from extra sensors and new outer shells, I want to do more playing with controllers. I have an Arduino Joystick shield, Arduino Nano and serial Bluetooth breakout board coming from China. It’d be cool to make some sort of interesting custom controller case with the Arudino controlling the car. I may also get an Arduino Esplora.
The other really obvious one is to stick with the RPi and pair a Wiimote to it too. That could be the ultimate controller for the car.
One downside of the i-Racer is that Arexx, the Chinese manufacturers, have not released the source-code to their Android App, only to the car software itself. Given how trivially simple the control protocol is, it should be very easy for someone to create Open Source equivalents for Android and iOS or even WP8 or BB10. I’m currently poking around inside PhoneGap’s Bluetooth support (this plugin) to see if a simple cross-platform Mobile Hybrid App could be created.
If this is a success, with success being defined as Fionn remaining interested, then I’ll bite the bullet and start getting the parts for one of the good Arduino robot kits out there. A good intermediate step might be the Sparkfun Protosnap Minibot Kit. After that, the sky is the limit:
This post was prompted by @mollydot asking me last night on Twitter what accessories make sense if you are buying a Raspberry Pi as a Christmas Gift and @jkeyes rightly suggesting that a post with links would be useful.
I really think this Christmas could be a lovely replay of 1982 for a lot of people, like me, who got their first home computer that year. You could have so much fun on Christmas Day messing with the RPi rather than falling asleep in front of the fire. Just don’t fight over who gets the telly when Doctor Who is on.
Whilst the bare-bones nature of the Raspberry Pi is wonderful, it is unusable out of the box unless you are a house with smartphones, digital cameras and existing PCs already that you can raid for components.
What you want to avoid is a repeat of me that December in 1982 with my brand-new 16K ZX Spectrum which didn’t work on our Nordmende TV until two weeks later when the RTV Rentals guy came and replaced the TV Tuner. Two weeks typing Beep 1,2 to make sure it wasn’t broken.
You can get it online from Farnell Element 14. Also most of the accessories I mention below. They are quoting a 3 week delivery time so get your skates on.
And available online from RS Components. They have lots of accessories too.
Orrrrr, you can skip everything I have written below and just get the Maplin Starter Kit for Raspberry Pi. Unusually for them, it’s actually decent value and you know all of the components have been tested for compatibility. There weren’t any in Blackpool in Cork the last time I was there so ring-ahead or order online.
An SD Card
I got these very cheap 16GB ones from 7DayShop in Jersey but the casing on one has shattered after very little use. They have branded ones which should have better quality plastic.
Micro-SD cards in an adapter work fine too.
Get the fastest one you can. Class 10 for full SD works great as does Class 6 on MicroSD.
Any size from 4GB up should be fine initially.
A Micro-USB phone charger
I’m currently using the one from my HTC Sensation.
Anything above 700mA should be fine but that excludes most cheap 500mA chargers that come with Chinese electronics.
I’ve had success with a some of the cheap ones from DX.com in China but many of the so-called 2 Amp ones can barely do 1 Amp so it might be best to avoid. Also, be warned, delivery times from DX can range from a week to many months.
I was very surprised to see an entire shelf of power supplies in a small Maplin in London but not one Micro-USB charger. As a place where a lot of people go to get emergency replacements for things, they should surely have tons of these?
TV Cables
If the person you are buying for has an LCD/Plasma TV then any HDMI cable will be fine. I have used ones from DX and Lidl with no problems.
If they have a older CRT TV then they will need a video cable with RCA at both ends and an audio cable with 3.5″ headphone jack at one end and RCA at the other end. If the TV takes RCA then that’s all they need.
If the TV only takes SCART, then you need an RCA to SCART adapter. Most TV shops have these. Maplin definitely do.
If they have a monitor with DVI then there are HDMI-DVI adapters. Neither of the adapters on DX worked for me. See this page for a list of compatible adapters.
If they have a monitor with VGA then this adapter on eBay _may_ work. Note that it works for me on two monitors here but totally failed on a projector at an event during the summer.
USB Keyboard and Mouse
I haven’t found a wireless one which doesn’t work. Lidl and Aldi both great for these at the right time of the year. Otherwise anywhere online or PC World.
Not all wired keyboards will work as they may draw too much current. I have one roll-up rubber one (don’t ask) which shuts the RPi down when I connect it.
I found a dirt-cheap Microsoft wired Keyboard/Mouse for about €15 last year in Dixons
Powered USB Hub
USB remains a very frustrating experience on the Raspberry Pi. Unlike a PC, it seems to be a crap-shoot as to whether something will work on it or not. The problem is the tiny amount of power the two USB ports can provide (150mA compared to 500mA on most PCs) and some ongoing problems in the drivers.
The best way to avoid this is to get a USB hub that can be externally powered and connect all devices to that. Unfortunately, many of the dirt cheap ones out there that have a power connector don’t actually work with power connected.
This extremely cheap hub ($5!) that I got on DX last week seems to be working really well so far. It doesn’t come with a power supply but accepts one. You’ll have to find a 5V one yourself with that smaller size of power jack.
If you continue to have problems then you may be forced (as I was) to hack the USB cable from the hub to the RPi and disconnect the power lines so that the Hub isn’t sending power back up to the RPi
Wireless Adapter
Whilst the RPi has an Ethernet port, it’s not really that useful for many people whose broadband routers are in the hall. One of our RPis is wired but that’s because we run GigE cabling everywhere.
I have a ton of Wifi adapters collected over the years. Most of them work on the RPi.
I’m currently using some random Wireless-G one to stream a webcam internally.
We had some good fun last night with the neighbourhood kids making use of our Doorbell of Dooooooooommmmmmmm.
I’ve had a bigger doorbell project planned for quite a while but 2 weeks ago decided we should do a simpler Halloween one. Using various bits bought from Sparkfun and Maplin along with a great tutorial from Adafruit (more below), I finally got something we were happy with, working late last week. Then yesterday evening I put it in place on the door. Unfortunately, with all the pulling, taping and general movement, one of the five buttons stopped working. But the other 4 were fine.
The sounds used were pulled from various online sources. Sibéal came up with the Mr Burns idea and Oisín thought of the Home Alone one. I used Audacity to clip some of them and ffmpeg to convert some of the YouTube videos to audio. The cheques are in the post
Originally I was going to use Arduino for this but considering a Waveshield for playing audio costs more than a Raspberry Pi, I changed direction. I then thought I’d use the Arduino for the button detection and communicate over USB to the RPi but I finally realised I should just use the GPIO pins directly on the RPi itself. My worry about killing it accidentally were unfounded.
The first version was done on a breadboard to make sure I made no mistakes. It worked well. But it was never going to work stuck to a doorframe so I moved to a strip of veroboard and soldered it together. This had a few, ahem, glitches, which took a while to sort out due to my soldering incompetence.
The final setup was really simple:
One button per sound
Each button connected to a GPIO pin on the RPi along with connection to 3.3V and GND on the RPi (pull up resistors there too but apparently not necessary?)
An old 40-core IDE cable from a dead PC used to safely connect the wires from the buttons to the pins on the RPi.
Extremely simple Python code running in a loop on the RPi which checked to see if any of the connected pins were pulled low by the button being pressed.
If so, it made an external call to mplayer to play one of our selected audio clips
The only real change from the Adafruit tutorial was to use mplayer instead of mpg123. This allowed me to use any audio format including WAV, rather than just MP3s. Also some of the instructions are a little redundant with the latest version of Debian on RPi, but they do no harm.
This is the trivial script to set the volume and call the Python script:
This is the code, it uses the RPi.GPIO library (the latest version works fine):
#!/usr/bin/env python
from time import sleep
import os
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(22, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(24, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(25, GPIO.IN, pull_up_down=GPIO.PUD_UP)
while True:
if ( GPIO.input(22) == False ):
os.system('mplayer /home/pi/haunted_sounds/Howl.mp3 &')
sleep(3);
# if ( GPIO.input(17) == False ):
# os.system('mplayer /home/pi/haunted_sounds/HomeAloneCountOf10.mp3 &')
# sleep(3);
if ( GPIO.input(23) == False ):
os.system('mplayer /home/pi/haunted_sounds/ReleaseTheHounds.wav &')
sleep(3);
if ( GPIO.input(24) == False ):
os.system('mplayer /home/pi/haunted_sounds/Scream.wav &')
sleep(3);
if ( GPIO.input(25) == False ):
os.system('mplayer /home/pi/haunted_sounds/CastleThunder.wav &')
sleep(4);
This diagram of the RPi pin-out was invaluable:
Once everything was setup at the door yesterday, we then found that the volume on the Lidl iPod Dock was far too low. I had to put a tiny battery powered speaker outside, taped to the postbox. But even that wasn’t great so I added a Fiio amplifier. Of course then we couldn’t hear it inside, so I split the audio and used one audio device inside and one outside.
I didn’t have time to setup wireless on the RPi so I used a wired network connection. This enabled me to SSH to the RPi from my PC and start the Python program. It also allowed me to remotely change the Home Alone clip to the howl from An American Werewolf in London after it got a bit tiresome, 2 hours later.
I made a video of it all in action but the bloody version of CM10 on my phone corrupted it. To give you a taste of what it was like, I extracted the audio from it. Enjoy:
Changes? Instead of externally calling mplayer, it’d be better to use some sort of audio library that would allow a follow-on button-press to interrupt whatever is playing. Also, approx 75% of kids pressed the top button so the next time we’ll randomise what is played.
Next steps? Well that’d be our Social-Enabled Doorbell. It’ll probably be Christmas before I finish it tho.
This post was going to be just an up-to-date summary of many other articles out there on this subject. With the rapid rate of change in the RPi world, even very recent guides have proven to be unusable quite quickly.
However I’d first like to remember Mike Singleton who died last week. I didn’t know his name until today when I read this lovely piece about him. But what I did know about was Lords of Midnight and Doomdark’s Revenge. Those two adventure games dominated that category on the ZX Spectrum in the mid-80s. Mike was still creating new games until very recently. It’s just another reminder of how important the 1980s UK home computer scene has been to the current gaming industry. In memory of Mike, I’m playing Lords of Midnight from the start again this evening on the Raspberry Pi. RIP.
The Raspberry Pi makes a brilliant base for old-school game emulation, just as it does for XBMC. You literally just need it, a USB joystick, maybe a wireless dongle, a TV and you are in business. I’ve been very tempted to double-sided-sticky-tape one to the side of the TV without a case, it’s that small. I’m currently using an ancient 14″ Philips portable CRT to get the full retro effect, including blinding flickering.
Atari 2600
OK, I have to admit my rose-tinted spectacle were on overdrive here. The Atari 2600 Pacman in my head was actually the arcade version. The real thing is pretty awful. This console was a bit before my time and the main thing I remember about it were the completely unusable joysticks. But if you want to re-live that horror, then it’s really very simple.
Grab all the Atari 2600 ROMs from one of many sites. They are tiny so the download takes no time at all.
Then install the Stella emulator:
sudo apt-get install stella
Then just run stella inside X Windows. More details here.
MAME Arcade
MAME seems to have been around forever. It enables you to play old arcade games on a wide variety of machines. I remember using it on my brother-in-law’s Atari 520ST in the 90s.
So it’s no surprise it works well on the Raspberry Pi. Compiling from source apparently takes forever and some of the binaries from this summer don’t work on the latest Debian release. However this latest compiled version of Advance MAME by Shea Silverman runs perfectly on the latest Debian.
