On Tue, 2005-03-15 at 08:55 +0000, Peter Washington wrote: [...]
I'm a bit of a newcomer, (complete virgin actually), to newsgroups and mailing list, so please bear with me.
That's okay; I'll help you with the mailing lists if you'll help me with the hardware...
[...]
- Trust the Maxim datasheets over any other source. (I think the Hardware Recyling circuit has used 0.1mF to 0.1 micro Farads, lack of the Greek mu)
- Putting Vcc into the Gnd Pin of any chip will definitely damage it IF any other pin is connected to a voltage around about Vcc.
The "Magic Blue Smoke" gets boiled off and it stops working ;-(
There's actually good, if rather embarassing, news. The reason why I was getting a voltage drop of zero across Gnd and Vcc was not, as I thought, because the MAX232 was short-circuiting the power supply --- it was because it wasn't connected to the power supply! I hadn't noticed that the breadboard I was using had a break in the power rails halfway across, and of course I'd plugged the power supply in on the left and the circuit in on the right... I think the only useful thing I can say at this point is "D'oh!".
So after plugging everything in the right place, I powered it all up again and it seems to be much better behaved. All the voltages seem to be correct, so the charge pump is pumping and it generally seems to be doing its thing.
Still doesn't work, though; but seeing as when I connect TX and RX together on the jack, I get garbage instead of seeing my input echoed back, I suspect there's a wiring problem somewhere. I'll try to scrounge up a scope and have a look this evening.
[Incidentally, I've discovered that the HAM radio set use pretty exactly this kind of interface --- you can buy readymade cables for under twenty quid. Pricy, but unlike the stuff I build it should work... it might be worth looking at TI calculator cables, too.)