Today, I’ve had an eventful day – not only have I received my small, test order from RS Components, I have also received the Nixie tubes and power supply boards. We chose to order 16 Nixie tubes – five for each 8-bit input register and six for the output register. Separate flyback boost converters are needed for the Nixie tubes as they operate at 120V which we are unable to supply directly.
I have yet to power up the tubes, but I’ll be sure to post some pictures when I do – they should give the TwitALU that vintage feel that we’ve been after.
The parts that I ordered from RS Components included a whole range of 3mm LEDs so that we can decide on which colour and intensity to use. I also ordered three of the specific relays that we aim to use so that I can construct one 1-bit full adder for test purposes.
As soon as I received the parts, I ripped open the RS packaging and used my Arduino to switch the contacts on the relay. Immediately, I ran into a problem that the Arduino could not sink enough current when powered from its USB port, an extra 9V, 2A power supply was used to give the Arduino the extra oomph that it needed. This means that the CMOS 7400 logic chips probably won’t be able to drive the coil directly and some sort of buffering system is needed. I’m hoping that there is a DIL package octal buffer that can supply enough current, but I will have to do more research.
This testing does mean some modification to the 8-bit relay full adder PCB has to be made – but it is much better to discover and correct these issues now and before the PCBs are manufactured.