Atmel 328p showing 1.2v

Hi

I have a 328p chip soldered on a custom pcb but it is not working as expected.

Now the voltage between vcc pin and GND pin is showing to be at 1.2 v
i am using lm7805 to convert 12 dc to 5v dc . and i am uploading a blink sketch .
but i am unable to upload.
output of lm7805 is exactly 5v and chip is directly connected to the 5v.

Is something shorting ?

Hi,
Can you post a schematic of your project?
Can you post a diagram of your custom PCB? (Export an image in jpg)

If Vcc of the 328 is supposed to be connected to the LM7805, it seems as though you have some resistance in the track between the two.
If you remove the 328, I hope it is in a socket, what voltage do you measure at the pin pads on the PCB.
Check all your tracks with DMM.

Thanks.. Tom.. :slight_smile:

From you post it would point to the grounds, however its best to troubleshoot some more.

I would suggest you connect your multimeter ground at one point, perhaps where power enters the board. Without moving the multimeter ground, read the voltage at:

All measurement should be made at the corresponding pin of the device(s).

  • Input to the 7805
  • output of the 7805
  • ground of 7805
  • Vcc of the 328p, also report what pin on the package are you reading
  • ground of the 328p, also report what pin on the package are you reading

Looking at your readings, do all of this make sense?

manveen_singh:
Is something shorting ?

Does anything get hot?

(results in the same answer).

Schematic is needed for an educated guess on what's going wrong.

The first thing I would check after verifying that you have 12VDC is if you have proper bypassing on the 5V regulator and that the caps are very close to regulator, < 1". I am just guessing but I have seen this many times.
Good Luck, Have Fun,
Gil