Hi. I have a USBtinyISP, an Atmel ICE and a mid 2010 MacBookPro (MBP from now on).
I use the USBtinyISP to program my own ATmega328 boards, described here: https://hackaday.io/project/11724-yauvc ... controller
I power up those boards from a switching power supply, regulated at 3.3V. The USBtiny jumper is removed to do so.
I find issues with the MBP every time I connect the boards to the USBtiny when it is connected to the MBP. Same issues happen if the board is connected to the USBtiny and I connect the USBtiny to the MBP USB. In both cases the USBtiny is not recognized by the MBP. To fix them I have to disconnect everything and reconnect, keeping only the power supply ground connected to the bundle.
I'm going to say this again: Only power supply ground *must* be connected to the board->USBtiny when these are connected to the MBP. Than the red led from USBtiny turns on and USBtiny is recognized. That is an issue.
It is obviously a ground problem. My MBP uses a 2 pin adapter to connect to the wall. I ordered a 3 pin adapter that grounds the MBP, and while it does not arrive, I managed to ground the Apple power adapter myself. But the problem persists.
I have a second monitor connected to the MBP and sometimes, when I plug in the USBtiny the second monitor looses the image and gets blank. Nothing else happens. No smoke, no burning.
Now comes the news. Yesterday the USBtiny stopped working. All I get is an initialization failure, cannot read device signature (0,0,0) from avrdude. I switched to the Atmel ICE and could program the boards.
I tried many solutions, rechecked the flat cable connections end got no results. I even remelted all the USBtiny solders without success.
I read somewhere that 99% of the time the problems with USBtiny are wiring ones. I believe, by changing the programmer, that I do not have wiring problems. That is why I'd like to ask you what happens on 1% of the time? Should I substitute one of the ICs?