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I currently use a Pololu USB AVR Programmer v2.1 for programming 328p chips and I really like it. The ability to have ISP and Serial in one physical device, enumerating as two separate COM ports on the PC, the programmer powering the circuit at 3.3v, with the programmers windows GUI interface to set voltages, programming frequency and give feedback on the programming when things go wrong, is all brilliant.

However, many of my circuits either have a power requirement higher than that on the Pololu (80mA), or to much capacitance (33uF) so that the power surge on connection is too much for the Pololu and it resets. The reset disconnects my serial debugger, disconnects the Pololu GUI, and sometimes does not come back on at all due to the startup current draw.

I am looking for suggestions for an alternative device, or way of stopping the brown out on power up?

Thanks very much Kevin

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  • To clarify, you are avoiding powering your programmer from the target's VCC because you don't want the programmer to re-enumerate when the target power-cycles, correct? – timemage Dec 19 '20 at 16:33
  • Hi, I want the targets VCC to be 3.3v from the programmer, so that I don't have to provide a separate power supply. It is normally Solar powered - but that is difficult inside in the winter in the UK :) – Kevin W Dec 20 '20 at 17:00
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How about, connecting a tiny battery across the 3.3v output of the Pololu. Lets assume a 3.7v LiPo, charged to 3.3v.

When the battery is connected at 3.3v, no current will flow.

When my device to be programmed is connected it will draw a spike of current, which will start to take the Pololu below 3.3v, but then the LiPo will start supplying current and stop the Pololu voltage getting dragged down and browning out.

The LiPo will then be slightly below 3.3v, so will get a Constant Voltage charge back to 3.3v.

Two potential issues I can see:

  1. When the Pololu is disconnected from the USB will it be being 'back powered' by the LiPo?

  2. When in CV charge mode, the only current limiting will be internal resistance of the Pololu output / LiPo cell, probably not an issue in practice due to the voltage drop being very small.

I know it is a hack, but thoughts welcomed.

Cheers Kev

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