Quote:
Originally Posted by SiriusHardware
One consideration when basing it on any common microcontroller board is how much current the programmer hardware will need during programming pulses - potentially quite a lot, and if the supply to the Arduino (or whatever) is limited to the standard USB 500mA then it could be necessary to organise an independent more current capable 5V supply for the programmer hardware. In Chris's original Acorn based version this won't have been a significant problem because the +5V supply was presumably drawn from a more than adequate +5V supply on the rack it was meant to be plugged into.
Raspberry Pi Zero and Pi 4 apparently pass their +5V supply unfused to the +5V output pin on the GPIO port and both devices presumably negotiate for more than 500mA from whatever micro USB supply they are powered from.
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On my design all the voltages for programming are supplied through a separate 12v power supply to the sheild. There is a separate buck converter and bulk capacitance that converts this 12v down to 10.5v for programming and 5v for other logic. Only the Arduino itself receives power through the USB when plugged into the computer. I did this because I imagined most people could lay their hands on a 12v 2A ish wall wart.