False Low Battery Warning

Hello all,

Just finished installing a Fallen v2 yesterday and I am getting a false “low battery” warning at random. It usually triggers right away (within 30 sec of powering up).

Full disclosure: This board was purchased second hand and prior owner did attempt install. There was some minimal soldering done and visually board looks fine. Just seeing if anyone else has ideas what to test before I give up and get another board

Below is what I have tried so far:

  1. Three different batteries (all 4.1v on multimeter)

  2. Different SD card

  3. Uploaded config again, doubled checked correct Proffie v2 selected

  4. Metered battery +/- pads on the board and reads 4.1v when battery is plugged in

  5. Continuity test from Batt + pad to all other pads on board. No shorts found

  6. Thoroughly inspected and cleaned all joints and wires

Any guidance would be appreciated.

What does “batt” say in the serial monitor?
What version of ProffieOS do you use?
What version of the arduino-proffieboard plugin do you have?
Could you post your config file?

ProffieOS averages many readings on the battery, but maybe in your case it needs more averaging.
If so, you could try changing this:

Finally, I should mention that the battery monitor circuit is fairly sensitive to stuff touching it. Especially if the thing that is touching is it semi-conductive. If I remember correctly, the circuit is roughly in the middle of the board on the bottom. (Same side as SD card.)

What does “batt” say in the serial monitor? 2.84v
What version of ProffieOS do you use? 5.9
What version of the arduino-proffieboard plugin do you have? 2.2.0? Is this under Tools>Boards>Boards Manager?
Could you post your config file? Fallen v2 Config - Pastebin.com

Regarding the circuit, I get the error even with the board hanging loose from the chassis, not taped down with wires crammed in lol

The only thing I did with wiring which may be a little unorthodox is run the accent pixel off the 3.3v pad. It is a single neopixel, so I figured it wouldn’t be an issue

That’s pretty low.
Is that with the blade ignited, or off?
Is it always that low, or does it fluctuate?
When the battery is actually low, does the serial monitor values go even lower, or does it just stay at 2.84v?

I don’t think the LED on 3.3v should be an issue.
Have you measured the 3.3v pad to make sure it’s still at 3.3 volts?

That is with the blade off. I am not very familiar with the serial monitor and how to use it. Sorry

3.3v pad reads 3.9v

Welcome to ProffieOS, type ‘help’ for more info.
Battery voltage: 2.81
Amplifier off.
Unmounting SD Card.
Battery voltage: 2.78
EVENT: Power-Pressed#1 millis=284863
EVENT: Power-Pressed millis=284863
Motion setup … I2C init…
EVENT: Power-Released#1 millis=284864
EVENT: Power-Released millis=284864
EVENT: Power-Shortclick#1 millis=284864
EVENT: Power-Shortclick millis=284864
ACCEL: {0.09, -0.46, 0.36} diff={0.42, -0.18, -0.95} v=1.06 fgl=0.01 accel_={-0.16, -0.32, 0.99} clear=0 millis=284872 swing_speed=1.38 mss={0.04, -0.36, -0.98} stab=0
EVENT: Swing millis=284889
EVENT: Power-SavedShortclick#1 millis=285164
unit = 0 vol = 0.00, Playing Survivor/hum/hum01.wav
channels: 1 rate: 44100 bits: 16
unit = 1 vol = 0.50, Playing Survivor/out/out05.wav
channels: 1 rate: 44100 bits: 16
humstart: 1800
unit = 2 vol = 0.50, Playing Survivor/swingl/swingl01.wav
channels: 1 rate: 44100 bits: 16
unit = 3 vol = 0.50, Playing Survivor/swingh/swingh01.wav
channels: 1 rate: 44100 bits: 16
Battery voltage: 2.78
Playing Survivor/swingh/swingh01.wav
channels: 1 rate: 44100 bits: 16

Ouch, that’s bad.
That will eventually burn your board, and it might also be the reason the battery level is wrong.
The CPU is not meant to operate over 3.6 volts!
If that’s somehow caused by the LED you connected to the 3.3v pad, then I suggest disconnecting it immediately.

I will unsolder all the pads connected to the LED and try that

I removed all wires from the board going to the accent pixel and still got the low battery

I swapped the board out and connected all wires including the accent pixel and all is right in the universe.

I guess somehow the person who tried to install previously burned something up internally in the other board.

Appreciate the help

Does the 3.3v pad still read as 3.9 volts?

Nope, reads 3.3v now

Besides the CPU itself, there are only two components involved with reading the battery voltage: R1 & R2 These are 410kohm resistors, but almost any size resistor from 100k to 500k will work as long as they are both the same.

Might be worth taking a look at them and see if they look ok at least.

Looking at those resistors under a magnifying glass, they look OK visually. I do not see any signs of excess heat or misplaced solder anywhere on the board for that matter.

I am going to try using the board again on my next install, maybe try LED 2/3 instead of 4/5 or something. Maybe get lucky lol

You can also measure the voltage between two resistors.
It should be exactly half the battery voltage.

I just checked this board. It’s saying low battery, Serial Monitor says 2.78.
The 3.3v pad and SD power pad are 4.8v with a 4.13v charged battery.
The resistors R1 and R2 must be in flux while power is applied, I can’t get a reading. With no power they steadily climb from the 200’s up to about 318 \Omega
Voltage across R1 R2 is 2.08v.

Is 5v shorted with 3.3v somehow??? If not, I don’t see how this is possible.
(Unless you’re measuring it wrong.)

You can only measure resistance when the board is unpowered, and it’s not always going to work perfectly. However, when it’s powered you can measure the voltage on the voltage divider. One end should read 0, one should read battery voltage and the middle should read battery voltage / 2.

The only place the 3.3v pad beeps is to a Q7 leg.
5v pad only beeps on a U3 leg.

It’s a solid 4.8v on the 3.3v pad, while 5v does actual 5v when sound is running.

I suppose the short could be under/near the 3.3v regulator.
Is it plugged into USB? Maybe it’s getting the 5 volts from there…
(Check both sides of D61?)

USB only, 3.3v pad still 4.8v
Batt pad side of D61 is .96
Board side is the same 4.8
Batt connected, D61 shows 4.8 still