Well, I work with software (mostly developing it), I work with Linux systems from embedded to hpc. When asked why something doesn’t work, I am known for telling people to “RTFM!”. My favourite, when some muppet distinguished colleague says they don’t know how to use the Unix “man” command is to point out that they can “man man” to figure it out 🙂

When it comes to software and systems that I am familiar with then smug bastard am I.

Hardware. Hmmmm… I should probably eat my own dog food on that too. As I hinted at in an earlier post (not that anybody reads this drivel, fortunately) I was worried about some itty-bitty transistor-itty thingy that I’d used. I think I was right to be worried.

Incompetence, in all it's gory

Incompetence, in all it’s gory

The said transistor is at C7-C9 on the middle board. When I connect all this stuff up then the LED comes alive but starts to “spazz out” (sorry for the technical terms) when it tries to light up more than 2 digits. That Maxim chip is very sensitive to voltage fluctuations, DMM says voltage is going from 4.98 to 4.6. That’s fluctuating then.

Transistor datasheets says:



So, I think that little tranny is limiting the current to 200mA. That’s my guess anyway and it fits with the varying voltage. If I connect the Pro Mini to an FTDI cable then it just works.

I think I can replace that with an N-Channel power MOSFET (I have a pile of them). I “believe” that they work at similar voltage levels so shouldn’t be an issue turning one on, or off. I can’t find that data in the datasheet because I don’t really know what I’m looking at. I guess I’m out of my depth and out of my comfort zone. Sod it! I’ll just blat one in and see what happens 🙂

There was one other mistake. I forgot to connect the ground rails on the board with the transistor on it. That took “seconds” to spot. Unfortunately, about 600 “seconds” of testing, faffing and generally getting nowhere. Whatever.

If I “charged” my “leisure” time at £1/hr I’d be seriously out of pocket on this already. Meh. I’m really enjoying all the faffery and learning about stuff I just assumed was “easy” because other people did it and I couldn’t be arsed 🙂

Onwards, and, er, whatever…

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