RE: my own avr devolopement programming board

kouruu — Sun, 08 Mar 2015 12:16:06 GMT

Looking at his picture and the guide he referred to, he only has 1 cap on the Vout. Having no decoupling caps on the Vin and Vout could give variations in the voltage, but it shouldn't be that low. That kind of behavior is usually due to either a short, no power or a failed device or passive.

RE: my own avr devolopement programming board

michaelwylie — Sun, 08 Mar 2015 07:41:16 GMT

You have the input and output caps on the regulator? It can be unstable without them.

RE: my own avr devolopement programming board

kouruu — Sun, 08 Mar 2015 06:51:42 GMT

I'm by no means an expert, but I would check for a short between your voltage rails and ground during your soldering. The 7805 shouldn't get hot without hooking up a big load on the 5v out ( which is is caused by the excess voltage from your 9v supply dissipated through heat. ) A short would allow the electrons to flow freely and force a high amp pull. Your 7805 would get hot and/or battery depending on short, if this is the case. Electricity will always follow the path of least resistance so if a short exists, it's unlikely you will get a voltage supply to the circuit. Another possibility would be a bad 7805. (Just cause it's new, that don't mean it works.)

One thing I forgot to mention, to see if you have a short, you can take a multimeter and set it to continuity. The meter will beep if you touch the leads together. touch them to you voltage rail and ground and if it beeps, you have a short. Also, on your 9v power supply I assumed you used a battery, but either it be a battery or power supply unit, check your in voltage and make sure it's giving you a DC 9V.

If this doesn't help, hopefully someone with more experience than myself can assist you.