Category Archives: Arduino

A model train set in a suitcase – a seemingly never ending project

Over the past two years I’ve been working on my largest and most complicated electronics project yet.  My work on the project has ebbed and flowed, but it’s mostly finished.  So I thought I’d start writing up some notes on it.

The initial inspiration was seeing Jeff Faust’s Arduino controlled z-scale train set. I’d been toying with the idea of getting a train set even since my first child was born, but space was very much a premium in the house. So z-scale appealed greatly. It didn’t take much of a leap to then consider putting the train set inside a suitcase, so it’d be easy to store. So after saving up for a little bit, I picked up a Marklin z-scale starter set. I also picked up a turnout, a decoupler and a bit more track, so there was a little bit more interest to the layout.

Seeing what the z-scale layout looks like in suitcase with scenery mostly done

Although, it’s not finished, I wanted to get some of this written up now. If I wait till it’s actually finished it may be a long time. Hopefully I’ll go into more detail on a few bits at a later date as well. From an electronics point of view there are quite a few “modules” that would justify individual blog posts. For now I’m just going to provide an overview of my progress to date.

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A couple of ATtiny projects (ARC reactor + lighthouse)

Here are a couple of the other ATtiny projects I’ve worked on.  Only now just writing them up.  They are both pretty simple.

The first was an Iron Man style “ARC reactor” (the circle light in his chest) that I made to go with my son’s (shop bought) Iron Man costume.  It was just three blue LEDs covered in translucent Fimo, that light up in sequence, stay lit for a few seconds, then shut off in sequence.

Arc reactor on Iron Man costume

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Re-configuring the HC-06 (cheap) bluetooth serial module

I picked up a cheap bluetooth serial (rs232) module from Amazon. As it didn’t cost too much, I thought I’d take a chance. The module arrived fine, though (unsurprisingly) without any documentation. Initially I’d tried following the documentation for configuring a HC-05 module, but after I while I realised it was actually a HC-06 module. The HC-06 is very similar to the HC-05, but (crucially) initially runs at a different baud rate (9600bps instead of 38400bps). Luckily I found some good instructions for configuring the HC-06 serial module elsewhere. I’m going to recap what I did to get the module working with my (OS X) laptop and a USB serial adapter. Initially I just connected the pins from the bluetooth module to the USB serial adapter directly. Although this meant that the power/ground pins lined up it also meant that the rx/tx (receive/transmit) pins also lined up – which we don’t actually want. We actually want the rx pin on the serial adapter to go to the tx pin on the bluetooth adapter (and vice-versa). This is because it’s not simply passing through the signals – instead we’re transmitting from the serial and receiving on the bluetooth adapter. This also means that we have to make sure the baud rates of both adapters match. You can see the pinouts of the bluetooth (top) and serial (bottom) adapters here: USB Bluetooth module (HC-06) and USB serial adapter I used a breadboard and some jumper wires so I could have rx and tx swapped over: Configuring HC-06 bluetooth module with USB serial adapter connected to laptop
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LeChuck from Monkey Island cross-stitch with animated LEDs driven by an ATtiny

After acquiring some aida and a set of fairly cheap embroidery silks, I decided to try my hand at cross-stitch. As with a lot of craft related activities cross-stitch and embroidery are having a resurgence. The fact that cross-stitch is essentially the first form of pixel-art makes it perfect for rendering old-school 8bit/16bit graphics. Heading over to the Sprite Database I found the sprite for LeChuck from Monkey Island 2: LeChuck’s Revenge.

Nearly finished LeChuck cross-stitch + frame, button and electronics

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Making a musical Robot Santa ornament using an ATtiny 85

William tests robot santa

In what is threatening to become a tradition, I made a Christmas ornament again this year. Last year I just made simple tree ornaments using sculpey and fimo.

This year things got a bit more involved, as I decided to make a musical model of the Robot Santa from Futurama. It was a good thing I started working on it in November, as it took quite a few evenings to get it all finished.

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Arduino powered, temperature sensing, RGB LED nightlight

About a year ago I started on a project to make a temperature controlled nightlight. I was inspired by seeing these lovely LED lamps styled as mushrooms growing out of pieces of wood. Those mushrooms were made out of glass, which was somewhat beyond my skills. However I then saw some had used translucent sculpey to make mushroom nightlights on instructables. So with that discovery it seemed like it would be rather simple to do…

The first job was to solder up a three colour (RGB) LED (a super bright one from oomlout):

Wires + RGB LED ready for coating in Fimo

I then covered the LED in translucent Fimo:

RGB LED and wires covered in Fimo

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“Ultimate” Arduino Doorbell – part 2 (Software)

As mentioned in the previous post about my arduino doorbell I wanted to get the doorbell and my Chumby talking.

As the Chumby runs Linux, is on the network and is able to run a recent version of Python (2.6) it seemed like it would be pretty easy to get it to send Growl notifications to the local network.

This did indeed prove fairly easy and involved three main activities:

  • Listening to the serial port for the doorbell to ring
  • Using Bonjour (formally Rendezvous)/Zeroconf to find computers on the network
  • Sending network Growl notifications to those computers

Getting Python and PySerial running on the Chumby is pretty easy. The Chumby simply listens for the doorbell to send the string ‘DING DONG’ and can then react as needed.

def listen_on_serial_port(port, network):
    ser = serial.Serial(port, 9600, timeout=1)
        while True:
            line = ser.readline()
            if line is not None:
                line = line.strip()
            if line == 'DING DONG':
        if ser:

port is the string representing the serial port (e.g. /dev/ttyUSB0). network is an object that handles the network notifications (see below).

The network object (an instance of Network) has two jobs. Firstly to find computers on the network (using PicoRendezvous – now called PicoBonjour) and secondly to send network growl notifications to those computers.

A background thread periodically calls Network.find, which uses multicast DNS (Bonjour/Zeroconf) to find the IP addresses of computers to notify:

class Network(object):
    title = 'Ding-Dong'
    description = 'Someone is at the door'
    password = None
    def __init__(self):
        self.growl_ips = []
        self.gntp_ips = []

    def _rendezvous(self, service):
        pr = PicoRendezvous()
        pr.replies = []
        return pr.query(service)
    def find(self):
        self.growl_ips = self._rendezvous('_growl._tcp.local.')
        self.gntp_ips  = self._rendezvous('_gntp._tcp.local.')
        def start(self):
        import threading
        t = threading.Thread(target=self._run)
    def _run(self):
        while True:

_growl._tcp.local. are computers that can handle Growl UDP packets and _gntp._tcp.local. those that can handle the newer GNTP protocol. Currently the former will be Mac OS X computers (running Growl) and the latter Windows computers (running Growl for Windows).

I had to tweak PicoRendezvous slightly to work round a bug on the Chumby version of Python, where socket.gethostname was returning the string '(None)', but otherwise this worked ok.

When the doorbell activates netgrowl is used to send Growl UDP packets to the IP addresses in growl_ips and the Python gntp library to notify those IP addresses in gntp_ips (but not those duplicated in growl_ips). For some reason my Macbook was appearing in both lists of IP addresses, so I made sure that the growl_ips took precedence.

    def send_growl_notification(self):
        growl_ips = self.growl_ips
        reg = GrowlRegistrationPacket(password=self.password)
        notify = GrowlNotificationPacket(title=self.title,
                    sticky=True, password=self.password)
        for ip in growl_ips:
            addr = (ip, GROWL_UDP_PORT)
            s = socket(AF_INET, SOCK_DGRAM)
            s.sendto(reg.payload(), addr)
            s.sendto(notify.payload(), addr)

    def send_gntp_notification(self):
        growl_ips = self.growl_ips
        gntp_ips  = self.gntp_ips
        # don't send to gntp if we can use growl
        gntp_ips = [ip for ip in gntp_ips if (ip not in growl_ips)]
        for ip in gntp_ips:
            growl = GrowlNotifier(
                applicationName = 'Doorbell',
                notifications = ['doorbell'],
                defaultNotifications = ['doorbell'],
                hostname = ip,
                password = self.password,
            result = growl.register()
            if not result:
            result = growl.notify(
                noteType = 'doorbell',
                title = self.title,
                description = self.description,
                sticky = True,

    def send_notification(self):
        send notification over the network

The code is pretty simple and will need some more tweaking. The notification has failed for some reason a couple of times, but does usually seem to work. I’ll need to start logging the doorbell activity to see what’s going on, but I suspect the Bonjour/Zeroconf is sometimes finding no computers. If so I’ll want to keep the previous found addresses hanging around for a little longer – just in case it’s a temporary glitch.

You can see the full code in my doorbell repository.

“Ultimate” Arduino Doorbell – part 1 (Hardware)

After a first couple of small Arduino projects I felt the need to make something a bit more useful and permanent.

I had seen Roo Reynolds talking about hacking his doorbell to get it onto Twitter and as our doorbell is a bit rubbish I thought this seemed like a good project. His hack only updated Twitter, so there was no direct physical sign that the doorbell had been rung. Given that our current doorbell is pretty rubbish anyway (it should ring, but just makes a rattling sound), I decided to start off with the physical/audible side of things and then later move on to pushing notifications out to laptops on the local network or beyond…

I’ve been documenting my progress on Flickr now for a while.

Take apart wireless doorbell

Following Roo’s approach, I picked up a cheap wireless doorbell from Tesco for about £9 and took it apart:

I was able to verify that I could turn an LED on/off with the doorbell at this stage, so I knew I could use that as a signal in the Arduino. Using a multimeter also let me figure out some more details about the voltage and current used to power the speaker:

Testing wireless doorbell with multi-meter

This was about 3.1 V and 75mA output. That’s a few milliamps more than the Arduino can tolerate, so I knew I had to make sure I put a resistor (22KOhm) in between the doorbell and the Arduino. The doorbell would also need to draw power from the Arduino, but luckily the Arduino has a separate 3V output, so that wasn’t an issue.

Testing connecting Arduino to doorbell

From there I verified that when the doorbell was activated I could read a drop in voltage from the wire on the doorbell labelled “SPI”. At this point I had the input for my Arduino.

Servos and prototypes

The next step was to provide some sort of audible output. Originally I had thought about just adding a buzzer, but fancied something a bit more old-fashioned. I figured it’d be good fun if the nice 21st century tech of the Arduino used some rather more ancient technology to create sound – a bell.

Using a micro servo from Oomlout I created a couple of prototypes.

I made a pretty simple circuit to hook up the servo, doorbell and arduino:

The first prototype used some lego and a bell from a Christmas ornament:

This worked, but the servo was probably louder than the bell!

Next I got hold of a small brass bell from a music shop. Luckily the top unscrewed and would let me easily attached it to a piece of lego. So another prototype was created using the small brass bell:

Prototype doorbell with brass bell

This worked much better!

The bell is about 100g in weight, which isn’t massive, but when it’s flung around the lego prototype would tend to move too. Not so good when this will live on the kitchen window sill. So I’d need something sturdier for the finished version.

A little soldering

As well as trying out a better bell I also made the circuit for the bell and servo more permanent, by soldering everything up on a piece of stripboard. I also used a few headers, so most of the circuit would plug into the Arduino – like a rudimentary shield. The wire to the pin controlling the servo, was left to be plugged in separately. I hadn’t soldered anything since school, so I ended up swearing quite a bit trying to do this. For me it was probably the trickiest part of the whole exercise, but it did work in the end. Just glad I had a multi-meter with a continuity mode to find the short-circuits – a knife worked well to clear up some of those.

Stripboard soldering

Full soldered doorbell + arduino


I next turned to my (t)rusty woodwork skills to create a sturdier version. First off some pieces of wood to mount the Arduino, doorbell circuit and servo:

Arduino and doorbell mounted on wood block

Servo mounted in wooden block

Next came the base and first part of the bell moving arm:

Then I added the top piece of the arm as well as the picture wire to make the bell swing properly:

Closeup of bell innards

At this point everything worked as expected:

Tidying up

After the sawing and sanding was finished there was still some general tidying up to do.

Once I’d taped down the servo wire and antena wire with electrical tape I needed to deal with the movement of the whole piece when the arm swings out. First I got hold of some Sugru and made some small rubberised feet to prevent the bell sliding around:

Sugru rubber feet on bell

The next task was to add a counter weight so the bell wouldn’t tip over. For this I made two piles of fifteen pennies, which I wrapped in electrical tape and taped to the ledge on the reverse side from the Arduino:

Counter weights on back/front of doorbell

Eventually these will be covered up and will probably actually make up part of the internal structure of the outer decoration. This should also mean they’ll end up being attached better. For now though electrical tape has proved sufficient.

One final tweak involved inserting some small nylon washers either side of the arm:

Washer and tidier wire

This was done to help make the movement of the arm more consistent and slightly smoother. Previously I was finding that the arm would shift position slightly, which sometimes caused problems for the servo.


With the hardware finished I then set about actually getting it all up and running as our real doorbell. So imagine my horror when upon placing the doorbell on our kitchen window sill and connecting the power everything went haywire and the arm just constantly moved! After some tweaking of the code and kitchen-side debugging I realised that I really should make use of the Arduino’s internal pullup resistors for the doorbell pin. Up until that point I had left it “floating”. When powered by the USB this rarely drifted to zero, so I thought it was working fine. However on mains power it regularly dropped quite low, making the Arduino think the button had been pressed, triggering the servo. Configured the pullup resistor and tweaking the activation threshold (as it was now higher than zero) sorted out this problem perfectly:


So we now have a slightly Heath Robinson doorbell. It works better that our old one. There’s also plenty of scope for making it do more too. In fact phase two will be mostly about connecting the doorbell to my Chumby to get it communicating with the local network.

Check out my doorbell git repository on github for the code, as well as a fritzing circuit file.

Chumby to Arduino communication using PySerial

So here are a few notes on getting a Chumby to talk to an Arduino using PySerial (and Python). It’s pretty easy, but I’ll document it to make it obvious. As the Chumby is sometimes a bit slow with a few of these steps, it’s good to know it will work in the end.

First you’ll want Python on the Chumby. At the time the latest version already compiled for the Chumby is Python 2.6, so it’s pretty up-to-date.

Once you’ve got Python installed and on a USB stick you’ll also want to download PySerial – I picked the latest version PySerial-2.5-rc2.

With PySerial expanded and on the USB stick (alongside Python) you’ll want to put the USB stick in the Chumby and connect to it via SSH.

Change to the directory for the USB stick (e.g. cd /mnt/usb).

You should see (at least) two directories, one for Python and one for PySerial:

chumby:/mnt/usb-EC5C-3D0A# ls -l
drwxr-xr-x    6 root     root         4096 Jun 26 21:15 pyserial-2.5-rc2
drwxrwxrwx    4 root     root         4096 Jan 10 13:51 python2.6-chumby

You’re first instinct may be to try and install PySerial via the usual call to python install. However this appears not to work.

All is not lost though – just manually copy the relevant directory (serial) from PySerial to the python site-packages directory, e.g.:

cp -r pyserial-2.5-rc2/serial python2.6-chumby/lib/python2.6/site-packages/

Know to check that’s worked open a python prompt and try to import the serial library:

chumby:/mnt/usb-EC5C-3D0A# python2.6-chumby/bin/python
Python 2.6.2 (r262:71600, May 23 2009, 22:28:43) 
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import serial

If you don’t see any errors (as above) then everything has installed ok.

Next step is to try out connecting an Arduino.

So first off you’ll want to ensure the Arduino has a program that can read from the serial port – to show that everything is working ok. In my case I picked my Morse Code program. This will read bytes from the serial port and toggle the built-in LED (on pin 13), so it’s handy for verifying the serial port is working.

So now you have a program loaded on the Arduino, connect it to the Chumby. The Arduino should get enough power from the Chumby to start up ok.

You need to work out which serial port the Arduino is using on the Chumby. List the tty’s in /dev and pick the most likely looking one (should have USB in it’s name):

chumby:/mnt/usb-EC5C-3D0A# ls /dev/tty*
/dev/tty      /dev/ttyS00   /dev/ttyS02   /dev/ttyS1    /dev/ttyS3
/dev/ttyS0    /dev/ttyS01   /dev/ttyS03   /dev/ttyS2    /dev/ttyUSB0

On my Chumby the serial port was /dev/ttyUSB0.

Now open up a python prompt again and try talking to the Arduino. You’ll need to configure the baud-rate of the serial port to match the program on the Chumby. In my case this was 9600.

chumby:/mnt/usb-EC5C-3D0A# python2.6-chumby/bin/python
Python 2.6.2 (r262:71600, May 23 2009, 22:28:43) 
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import serial
>>> ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=1)   
>>> ser.write('sos')

If you are using the same morse code program you should see the LED blink out ‘DOT-DOT-DOT DASH-DASH-DASH DOT-DOT-DOT’ – confirming that the serial port works.

This is really quite handy, as the Chumby is a small low-power Linux server. Coupled with Python this means it’s really easy to get any Arduino based project online, without needing a “normal” computer constantly running. Not quite as self-contained as using an Ethernet Shield, but the Chumby is fairly small, so it and an Arduino will easily sit on a window ledge (for example).