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Simple low voltage disconnect circuit for Arduino, feedback

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Simple low voltage disconnect circuit for Arduino, feedback

Preface:

  • Under impression to need a low voltage cut out, to prevent 2x AA NIMH rechargeable battery from being drained too now, and damaging them. (right??)
  • In deployment this circuit will commonly be exposed to complete discharge event if allowed.

Concept:

  1. S1 momentary switch is held down, activating Q1 to power up 328p
  2. Sketch begins and Setup() calls digitalWrite(A5, LOW)
  3. S1 can now be released as Q1 is held LOW by A5
  4. Battery gets low, triggering brown out detect (BOD), 328p resets, and disconnects Q1

Notes:

  • R1 is resistor wheel and i experimented with different values to get it to work. (as i have not done the math)
  • I have this assembled on breadboard, radio and lcd module are not pictured
  • With A5 disconnected it works well (while S1 held down), When off 0ma at Ammeter.
  • With A5 connected it can work with higher value of R1 (47k) to prevent it booting up itself, but when off Ammeter reads about 2ma.

This 2ma is still enough to drain the battery significantly if left flat for some time. Im guessing the 2ma and need for 47k resistor are related to what appears as A5 'leaking' while arduino off.

I have been able to reduce 2ma current consumption while off by putting pullup resistor between A5 and +V

I have limited space so need to keep things simple.

Feedback:

  • Any improvements / suggestions, to get around the leaky A5 issue ?
  • Or generally meet my design needs better ?

Circuit: