Hackable Badge Battery Voltage on Display?

shawnerz · 2015-11-08 21:18

Hello all.
I've got a newbie question. I have my badge. Played with the code. Everything works great. I thought I read a forum post that someone was able to get the badge to display its battery voltage. The gist of the thread was that it was not measuring properly.
I have searched but I cannot find that thread. I would like my badge to display the battery voltage as well. Oh, I poked around in github as well, and didn't find what I was looking for.
Is it a register I have to read from? Is there an ADC to query?
And just to verify, the Hackable Badge is built around a Propeller I, right?
Thank you very much in advance,
-Shawn

Mike Green · 2015-11-08 23:12

The Hackable Badge is indeed built around a Propeller.

I/O pin 0 (P0) of the Propeller is connected to an RC network with a 0.01uF capacitor charged from the battery through a 300K resistor. P0 is connected through a 1K resistor to the capacitor. You can set P0 to output a zero which will discharge the capacitor, then change P0 to input mode and measure how long it takes to charge up to the switching threshold of P0 (until P0 becomes a 1). There's some variation in the switching threshold from device to device and it will also change with the supply voltage. Best thing to do is to use an accurate voltmeter to calibrate this battery voltage measuring setup. There's a discussion of this technique in the Basic Stamp Reference Manual under the RCTIME statement and some discussion here.

JonnyMac · 2015-11-09 16:09

If you're programming the badge in Spin, here's a method that will read the RC circuit as Mike described (this counts on constants found in the eBadge base code).

pub read_battery | level 

'' Returns battery level
'' -- value returned is RC charge time in microseconds
'' -- will require calibration for volts

  level := 0

  ctra := %01100 << 26 | BATT_MON                                ' setup counter to measure low
  frqa := 1
  outa[BATT_MON] := 0
  
  repeat 4
    dira[BATT_MON] := 1                                          ' discharge rc
    waitcnt(cnt + (MS_001 << 1))
    dira[BATT_MON] := 0                                          ' allow RC to charge
    phsa := 0                                                    ' clear sample
    repeat until ina[BATT_MON]                                   ' wait until finished
    level += phsa                                                ' add sample to level

  ctra := 0                                                      ' release counter

  return (level >> 2) / US_001                                   ' return average of 4 reads

Hackable Badge Battery Voltage on Display?

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