Circuit problems.. DMM questions..
December 29, 2008
OK.. I just finish wiring up the first part of the new circuit board thats going into Ozzy. Basically the board has an attiny2313 + L293 thats a dedicated motor and servo driver. It has a 5v regulator too. The tiny takes serial commands from the main chips on the board. I don`t have the atmega168`s that will go in, so I wrote a simple test program on the Arduino to send serial commands and plugged in only ground, TXD and RXD wires. When I powered up my circuit board the arduino power LED came on!
I thought this was odd because the arduino is supposed to be USB powered. I tried to do some checks with a multimeter, but being a DMM n00b I come to ask the LMR electronic gurus..
1. From the ground bus to the chip sockets I get 5v. Great! But I also get 5v out of the TX or RX pin from the ATtiny. I assume this is where the Arduino was taking power from. Is either TX or RX pin supposed to be left high when theres no data moving?
2. I remove the battery and chips to check resistance in places. + to - of the battery plug has no connection, but if I reverse it and put the - multimeter lead on the + battery pin and same for the other theres about 8M resistance? Is this normal? It`s got a diode in to stop me putting the battery in wrong, I thought this would block the connection backwards?
3. Also if I put the - DMM lead on the ground bus and put the + lead on where there should be regulated 5v output the resistance bounces around between 300 to 5M ohm :| but after a while seems to settle on about 10k. Would the capacitors on the power supply do this?
I`ve got to take the board out and check the back tomorrow. I`ve probably just melted some wire insulation somewhere because I`m pretty hamfisted with my soldering iron. Other than that possibility I am stumped, so any help or suggestions would be appreciated. I can take a picture of the board or try to draw out the schematic if that helps.