Venturii Forum
General Discussion => Electronics => Topic started by: Cube on November 04, 2016, 09:11:28 AM
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I recently purchased a small batch of microcontrollers from Digikey for the Venturii VDAC-MID1 prototype board(s) I've been testing. Seeing that they were a whole dollar cheaper, I quickly browsed the datasheet and didn't notice anything drastically different from the standard 328P, so I bought 10 of them. I soldered the whole prototype together and powered it on. It was very exciting to see all the LEDs come to light, and optimism was mounting since nothing let out any smoke or even got warm. I pushed the VDAC firmware to the board and the status LED began to blink rapidly, indicating an idle CPU, and optimism was riding high.
That optimism was short-lived, however, as soon as I tried to connect to it through the VDAC module. Originally I used a USB-485 dongle but fell back to TTL when that didn't work, and quickly found that the TTL pins were inexplicably being pulled high by the MCU. I verified that there were no shorts in the PCB, and even removed the LED status indicators on the Tx and Rx pins, all to no avail. Suddenly that little B on the end of the MCU part number came back to mind, and I checked the datasheet for the UART pins. Relieved to find that they were unchanged from the 328P, other differences quickly became apparent and further reading on the Internet caused me to wonder if I had made a bad choice in selecting the cheaper option over the tried and true 328P?
I've got a batch of 328P MCUs coming in today, and hopefully Mark or Jeremie can float the 328PB off with their hot air rework stations. I don't have such a tool yet, and the prospect of removing the MCU with an iron is a little daunting, especially since I'd rather not damage the board in the process. I think I may have damaged one of the resistor pads when I removed it from the Rx pin - these prototype PCB's from OshPark are very nice, but I don't know how they will stand up to rework. Maybe that's why they give you three?
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The second revision of the Venturii VDAC MID-1 should be compatible with the 328PB MCU's, and you just have to override the device signature when uploading the binary to them with avrdude. That being said, I have not yet tested this as I only built one of the prototypes so far and we are saving the other two boards to try to build them with the Pick 'n Place machine.