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by Vurdentium 453 days ago
A) The timing for this is deliberately set to be very conservative in terms of the wakeup window (at the cost of higher power), so the radio is probably powered up for a good 5ms before the beacon arrives. I don't know if you could unintentionally design a 3V3 supply so poor that it takes in the order of milliseconds to adjust to an output current of about 30mA -> 80mA.

B) Yes, this is a fair point, and why I was careful to specify a "quiet" station above. If actively transmitting then there is likely a benefit to disabling power saving, but unlike Arduino bros I will admit at this point that I don't understand the WiFi spec well enough to comment further with any confidence.
2 comments
readmodifywrite 453 days ago
Not to mention the TX power ramps up in microseconds to quite a lot more than 80 mA.

If your supply can't handle the modem sleep mode it definitely isn't going to transmit reliably either.

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bobmcnamara 452 days ago
Often ESP32 devices at low power can still transmit, but will start to fail to receive acknowledgements.

I have a guess, but no real way to test what's happening. On the scope the start of a transmission says the supply hard, but most of the packet the ramp rate is relatively low. Once the transmission stops and the radio turns over to receive mode, the ramp rate is much faster. On a third device I can record packets and see that they are being sent and acknowledged, but often retransmitted by the ESP who didn't seem to hear the acknowledgement.

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bobmcnamara 452 days ago
> The timing for this is deliberately set to be very conservative in terms of the wakeup window (at the cost of higher power)

Yes, the minimum interval of when to start listening is determined by both radios clock accuracy budget, one of which can be known and the other assumed.

> so the radio is probably powered up for a good 5ms before the beacon arrives.

No, not anywhere near that long. I don't have a board wired out for current measurements, but for reference, 5ms/101ms beacon with DTIM=1 would be a 5% duty cycle without any useful data, unacceptably high for many battery powered devices.

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