electronics

Internally the BigTrak is a fairly typical modern toy, the circuit board in it with an epoxy covered ASIC in the middle looks like the main circuit board in any cheap radio controlled car. The motor driver H-bridges are built out of discreet transistors, but as the motors only draw about 25mA running current the transistors are nothing remarkable. Quite possibly the most expensive part is the 0.1" header that the keypad plugs into.

The H-bridge is a circuit used in electronic control of high current devices, particularly where the device polarity may be reversed, e.g. DC motors. The name comes from the fact that the circuit typically looks like a letter "H".

Actually I have a working RepRap now so it isn't all bad, but there are plenty (too many?) guides about what to do to make a RepRap, I thought I'd just point out the problems and mistakes I made building mine.

Video Graphics Array "VGA" is a standard for computer display. It has a lot going for it in the hobby electronics field as it is a pretty simple standard and quite straight forward to implement with sufficient signalling speed, there are also a lot of monitors around to test projects on! Colour is a lot easier to generate on a VGA monitor than on a composite video monitor, but it requires a lot more speed as the frames are more detailed and there are more signals to generate.

I recently received an enquiry about how the I/O throttling on the PIC worked to ensure that the PSP was shifting valid data out to the Z80. I had a look back at my code and figured out how I'd done it. However I realised in that conversation that the schematics for the project were vastly out of date and it seemed that I hadn't been keeping as up to date as I thought I was with my local copies.