Incredibly short RED blink or solid WHITE after powerup, Photon needs reset to work [Solved]

I’m not completely sure what’s happening here. Whenever I power up my Photon the first time it either blinks RED for a really short time, then dimly turns on D7; or, it will simply light up solid white.

The Photon is then stuck, when pressing the RESET button the Photon does what it’s supposed to do (start up, running it’s code, connecting to the Cloud, normal functionality).

The Photon is connected through Vin to a buck converter which converts 12+ volt to 5V. The buck converter has capacitors. The BUCK converter is turned on/off through a Voltage Supervisor (which turns of the circuit at 10.5 volts). When starting the power up, this supervisor takes a short amount of time (1/4th of a second) to calibrate, then it turns on the circuit.

What does this short RED or solid WHITE mean?

@Len, is the Photon RST pin being held low while the supervisor and buck turn on and calibrate? The RED/WHITE LED is not normal and may be indicative of a low voltage condition on Vin.

My logic behind is that the capacitors on the buck’s input and output take a while to be fully charged (if that’s the correct wording of it). Therefore a smaller voltage continues to the Photon which turns it on, but then it goes into this condition.

My voltage supervisor might also be the cause because I’ve already had a quite similar circuit (the same as this, but without the supervisor) and in that case it just worked.

RST pin is not held down, it is at the moment not connected so the internal pullup should be working fine.

@Len, what voltage supervisor chip are you using? You can slow down the Photon RST rise time by adding an RC circuit so it takes longer for RST to go HIGH then does your supervisor to calibrate.

I’m using the MAX6457,
I have version AANN, 0.5% hysterisis with 150ms timeout, but I’m going to switch to the AANM with 8.3% hysterisis and 50µs timeout.

How would I do this RC circuit? Interesting that I can influence this, I wasn’t aware of it. While resetting manually is not a problem at the moment, eventually we’re going to place several devices in a remote location in a casing, so it’s probably better if this is all in control.

@Len, there is an existing RC on the Photon that provides a 1ms or so delay:

You can add extra capacitance in parallel with C6 on your board to slow the rise time. However, with a 50us response time, the Photon should be ok.

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I’d figured about the 50 µs, however currently I’m using the 150 ms version. I’ll add an extra capacitor between GND and RST and experiment with some values. Any idea which one would be good? I was thinking between 1µF and 10µF.

@peekay123 small update, an extra capacitor did work, cool stuff! :smile:

For future reference and for other people: I first tried it with a 470µF 16V capacitor, this worked perfectly. In this circuit you also notice the capacitor needs to charge first, before the Photon turns on.

I then used a 10µF 50V capacitor, but this started blinking the device. The Photon turned on and off rapidly. This definitely is not the right value and considering this result I wasn’t sure a 22µF would do the trick either so I opted for the 100µF 16V which is perfect.