AVR usbisp stops working after i power the microcontroller

[jayanthyk192]

Hi,

I just built an AVR ISP programmer. I got it working and wrote a program on an ATMEGA128. I'm running this microcontroller off an SMPS(from an old comp.) I switched off the SMPS and after a few minutes switched ON the power. This rendered the USBISP to not work. Then i reconnected the USBISP and again it worked. Then I restarted the SMPS and again I had the same problem. I Tried this many times and had the same problem. What might be the problem? Please help.

Thank you.

 

[nandhu015]

The problem is with usbasp. You should connect usbasp after powering up the micro.

 

[jayanthyk192]

The problem is with usbasp. You should connect usbasp after powering up the micro.

What is the reason behind this? I could add something inbetween to stop this. I need to switch ON and OFF the MC.

 

[nandhu015]

You can try a buffer between usbasp and microcontroller.

 

[jayanthyk192]

You can try a buffer between usbasp and microcontroller.

I'm sorry, I forgot to update the thread. I tried it with a battery and it worked fine. So I added a switch inbetween the SMPS power line and MC. Now it's working fine. I even noticed that the usbasp goes into high impedance or input mode as any good programmer should. So I think the SMPS was giving a spike which made the usbasp to sleep or shutdown.