Predictably, I used a classical 555 astable circuit.

I studied a few circuits. I hoped to run my circuit on just one button battery, either a 1.5 or 3v. This led me towards transistor flip-flop circuits. I tried a few different circuits to no avail before my impatience pushed me to the 555.

I was hoping to make a circuit that would flash the LED for 50-100ms out of every second, so that the internet would run for weeks on one battery.

In choosing the 555, there were two compromises. Firstly I required two batteries instead of one (the 555 requires a minimum of 5v). Secondly I wouldn't be able to make a short flash for extended battery life as the 555 doesn't allow an off/low output longer than the on/high output.



The following is optional:

I prototyped the circuit on a breadboard.



I played about with resistors I had to hand. Using two 1 mega ohm resistors gave me a time of approximately 0.7 seconds low and 1.4 seconds high.

Watching the clip from The IT Crowd, the time period seems to be long, so this circuit is probably more accurate to the TV show than my short-flash idea.

If you've not done much electronics then prototyping can be a VERY good idea, allowing you to switch components and play around as you wish. Imagine soldering your circuit together and, after finding it not working, discovering it could have been solved in the prototype stage when you could easily change things.



I then soldered the circuit on the veroboard. One tool not mentioned thus far is a veroboard track cutter. This is a cross between a screwdriver and a drillbit, used to cut the copper tracks on veroboards (necessary when using DIL chips). These are, in my opinion, overpriced, so I just used a drillbit with my fingers.



I had already used a section of the stripboard for another project in progress, so I snapped off as much as possible, which probably wasn't enough. As you can see from my pictures, it is all a bit tight.

I am quite impressed at how compact I kepts the main parts of the circuit. The main problem was, as you can probably see, the CR2032 holders, which are bloody chunky and didn't fit so happily (there was enough space for one but the second wasn't so happy. Got it in eventually though).



As you can see from my photos, I haven't shown you the bottom (copper track) part of the circuit. That is because it is a monstrosity which should not be privy to prying eyes.





Also, the wires, you see, are curly. These are for connection to the LED are soldered between pin 3 on the 555 (the output pin) and the resistor (which goes to the negative rail, used to protect the LED).

I have curled them by wrapping them around a pencil. I did this so that they are more flexible, and just easier to deal with.



