Board populated with problems

A project log for Ricmohte

Ricohote? Ricmote? It's a remote for a Ricoh GR II camera.

morganmorgan 09/12/2019 at 02:132 Comments

I did end up populating one of the boards the other night and for the most part things went pretty smoothly. I'm please to say the #SOICbite Programming/Debug Connector Footprint worked brilliantly and will keep moving forward with it on this board, even if (likely) another revision is required. I even managed to have the clip on and all the wires connected on the first try! Flashed the ESP32 on the first try! I used my #ESProgrammer, which is showing all sorts of problems of it's own but is working...

So... onto the problems... First is a problem in selection for the SOICBite. The way I was thinking about this was, it's a programming interface, break out the things the ESP32 needs. The EN/IO0, TX/RX, 3.3V and Ground. This made flashing easy but, also that I could not test major parts of the board. I have a couple major power nets, VIN for example, is the combination of VBAT and VBUS (USB), switched by a P-Chan FET. The problems start with the fact I cannot test that part of the circuit.

What's worse is because I'm supplying 3.3V externally, testing the soft power switch has become increasingly difficult do to by the fact I have no idea what going on when I apply voltage to the AP2112 EN pin while there is already 3.3V on the output pin. In the little testing I've done so far, it does even appear power is flowing backward through the regulator. I've worked around this issue by not connecting the programmers 3.3V and connecting the USB cable for main power.

The only difference from this circuit is Q2 is an NPN transistor. This works in a revised version of the Falstad sim from the previous post and was the same part used in my test circuit. So far I have gotten it to work where it will power on but the latching just doesn't seem to be working. I'm using the same test code as before where BTN is an input pulled HIGH, but it just doesn't stay on. One notable difference in the test circuit was in that, VIN would be 3.3V and PWR_EN would have been hooked to the test boards 3.3V IN. Where as in the final board, the soft switch is attached to the AP2112 enable pin.

So. Next steps I guess I'm going to replace the NPN with a FET. Apparently, I don't use N-Chan MOSFETs. So I have to head to the hackerspace to dig one up. While I'm there I plan to probe through the entire circuit and document voltages to see if that sheds any more light on what's going on. Any suggestions would be appreciated.


Bharbour wrote 09/15/2019 at 20:06 point

Your comment about power flowing backward through the AP2112K regulator is correct. That is one of the not so great features of LDOs.

It looks to me like the GPIO on the BTN signal needs to be configured as an output and driving high to keep Q2 switched on and the gate of Q3 low enough to be switched on. Either an NPN (emitter grounded) or an N Channel FET should work OK for Q2. R4 could be a few K (3.3 - 4.7K) to reduce the base current if you use an NPN, but it should work and survive with the 330 that is there.

Since the output of Q3 is driving a fairly high impedence (3M), you might put a 50k or 100k pull down resistor on the Q3 drain-U2 EN signal to make it switch off more quickly when Q3 turns off.

The basic circuit should work as it is drawn.

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morgan wrote 09/12/2019 at 03:59 point

Womp, womp. Replacing the NPN with an N-Chan MOSFET didn't help.

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