I have designed a circuit that uses this low-battery-indicator: http://www.homemade-circuits.com/2013/05/low-battery-indicator-circuit-using-two.html
The circuit will be used in a buzz wire game that is placed outside. When the player completes the game the solenoid is activated to reveal some treats behind a trap door.
The solenoid is activated in three short 80ms bursts to make sure that the trap door mechanism is released. It fails to release one time of twenty but that is probably a mechanical issue.
The game is turned off while not in use and is activated by a switch when a lid is opened.
The game might be visited approx 5 times each week. Initially more frequently.
The target operating temperature range is from approx. +25°C in summer down to approx. -25°C in winter
- 4 PCS of 2V 15 mA standard indicator LEDs
- 1000uF 10V electrolytic capacitor
- Arduino Pro Mini Processor
- 1N4007 fallback diodes
- 1% 1/4W metal film resistors of various values (see schematics)
- 3V 15mA buzzer, operating voltage 2-5V
- HK 19F 5 V relay, 125 Ohm coil resistance
- JF-0530B 6V 300mA solenoid
Some current measurements:
- Arduino and one LED: 36 mA
- Arduino and two LEDs: 53 mA
- Arduino, one LED and the buzzer: 56 mA
- Arduino, two LEDs, the relay and the solenoid: 1.57 A
I set the low battery threshold indoors so that the low-battery-LED lights up at around 5.8 V.
The initial battery voltage reading with the circuit off is 6.5 V. With a 53mA load the voltage stabilizes at 6.1 V indoors.
But when I place the circuit outdoors for a while in approx 0°C the low-battery LED turns on even if the rest of the circuit works as intended. I measured the voltage outside and it reads 5.8V
When I take the circuit indoors again with the exact same batteries the low-power LED turns off and the Voltage level is back to 6.1 V
Is this a normal behavior? The circuit is meant to operate at -20°C. Will the voltage level be even lower at that temperature? Is there a way to prevent this from happening?