WS85 not starting after new build

[lsteiner13]

Hello,

I have just finished building 2 Breezedudes (2.3 HW).
For some reason my WS85 only starts randomly. When it starts everything works as it is supposed to. When it does not start, I see that the output voltage on the UART port drops from 3.3V to around 0.7V after connecting the WS85.
This happens on 2 different WS85 and 2 different Breezedude boards.

Any idea what could be the cause of this?

FW on the Breezedude is 1.0.4.
FW on the WS85 is 1.1.8.

Thanks a lot!

[thezenox]

I have seen this recently in combination with WS80 sensor on some boards during testing, but never happend to me on a WS85.
My guess is that the inrush current of the capacitors of WS sensor kills the P-MOSFET used for switching the power of sensor. But I don't know yet why it did never happen in the last 1.5 years.

Quick fix: Solder a wire from 3V3 on blue connector to VCC_WS (also labeled 3V3) on black connector. This bridges the (broken) MOSFET and puts a constant 3.3V to the sensor. You loose 'advanced under voltage protection' (so it is not possible to power off the sensor by software) but in normal use I have never seen a power issue where this would be required.

Ideale fix: Replace the MOSFET (Q1) by some 3-4A P-MOS (e.g. IRLML2244 or AO3401A) and add a 10 Ohm resistor inline with the VCC of the WS85 sensor. I already added this fix in HW2.4.

[lsteiner13]

Thanks for the quick answer - I guess I will give the quick fix a try!
What I have noticed is, that when the board is put in flash mode (double press on the reset button) and then connecting the WS85, the board restarts automatically but the WS85 turned on every time.
The supercap in the WS85 was empty during testing which I guess never happens when installed outside - maybe that's why this never happened to you.

[thezenox]

The "restart" when connecting the sensor is due to the 3.3V supply voltage dropping because of the surge and causing a brownout reset of the MCU.

You say it always turn on when connected in bootloader mode, then your MOSFET still seems is such good condition, that it can supply the sensor enough current to start. I will check that if I have a broken one again.

Non Solder Quick fix: (if you have another JST PH-4 housing, or just shrinktube it as single pin) pin-out the crimp terminal of the black connector and put it in the same position on the blue connector.