This project involves high voltages that will definitely hurt like hell and probably kill you if you touch the wrong bits when powered up (170V @ up to 45ma DC). Do not attempt to build this unless you are comfortable with HV safety practices and know how to solder and assemble PCBs. It is not a forgiving design and if you plug something in wrong you could cook a CPU or yourself! I'll not be going into step by step "what to solder where" instructions because if you need those then you are probably not of the required skill level to attempt this safely, sorry!

Before you embark on a project like this you should first make sure you can obtain the B7971 nixie tubes, these are becoming quite rare now and attracting high prices. It might take you a few months to track down enough, though you can start with as few as four tubes, it is easy to add extras as they turn up.

You might even decide to use a different display technology, fourteen and sixteen segment VFD tubes are quite readily available though they are a lot smaller than B7971. If you go down this route you will also have to make your own driver board(s) and replace the low level display routines in the code with appropriate code to drive your board.

Obtain a raspberry pi and install the latest raspbian distribution on it ( I used the minimal build with no GUI, just terminal access, feel free to use whatever you are comfortable with). Then install prerequisites thus:

sudo apt-get install graphicsmagick 
pip install twython

In order for the bot to have it's own twitter presence and be able to send and receive tweets from code running on the pi you'll need to set up a twitter account and obtain API keys for it. There is a good guide on this instructible. Keep these keys secret otherwise anyone might be able to impersonate your bot or just get it banned from twitter by spamming.

Nixiebot software is available on github (see links) download it and maybe give it a tweak to change the personality.

Now assemble the hardware, soldering up the smartsockets takes a while as there are many transistors and resistors on each one. Be careful with the tubes and be sure to be extra careful when straightening the pins. Too much movement can crack the glass to metal seal and you'll end up with an expensive dead tube (ask me how I know!) . Likewise you shouldn't need to exert too much pressure when inserting the tubes into the socket pins if you have straightened them properly. If you find you have to use force then you may be leaving residual strain on the pins once inserted which can cause problems with the seal after a while.

Full instructions can be found here.

Power:

The smartsockets each need 5V@ about 10ma, and 170V@ approx 20mA max. You'll not likely find one PSU that can power all the tubes at once, I currently run four Tayloredge 1363 modules to boost 12v up to 170V. Each module seems comfortable with up to three tubes running off it. Originally I used a bit of perfboard to house the PSUs and a 5V stepdown regulator to power the pi but have since made a PCB that has room for expansion if more tubes get added (see files). I got the PCB made by dirtypcbs.com in their protopack +-10 deal and have a fair few spares left over. If anyone is serious about making a large nixie array and feels they could use one of these boards then get in touch and I'll send one over :)

You don't have to use the tayloredge supplies, other PSUs are available, you could even roll your own, but do make sure it is up to supplying the current required by these big Nixies.

I use an old laptop PSU to supply 12V to the boosters and 5V regulator from mains.

Housing

Once all the boards and PSU are assembled you should house the sockets in some way. Currently nixiebot just has the smartsocket boards on standoffs which are epoxied to a baseplate for a minimalist look. I do plan to make something more fitting sometime. Whatever you make, it is best to mount the boards before wiring everything up.

Power wiring

Once the boards are fixed you can wire up the 0V, 5V and 170V connections on the smartsockets. If using multiple 170V supplies do not parallel up all the HV outputs (otherwise they will fight as the output voitage will not be exactly the same on each PSU) , just run each separately to the tube or group of tubes that it will power.

For the Pi I feed in 5V via the I/O header, you may want to go in via the USB sockets, your choice.

Data wiring

The Pi talks to the first smartsocket via its UART TX pin which is connected to the smartsocket RX. This board then has its TX pin connected to the next smartsocket's RX pin ... and so on, the smartsockets are daisychained and pass messages on down the line, only reacting to the messages that apply to them. Details are in the smartsocket protocol document

The tayloredge PSUs have a control line that can be used to turn the HV on or off via a GPIO on the Pi, my PSU board accommodates this line and includes a pulldown resistor. Future enhancements may well include adding a PIR sensor and only powering the displays when someone is in the room ( or when needed for a twitter photo request) So you may want to wire a GPIO pin to the HV control too.