I just saw this little gadget being released by HPI and thought I could improve on it.

Basically the HPI unit has a couple SMD leds that display the voltage ‘bar graph’ style but is always on. Yes, it won’t draw a huge amount of current, but if it drew ~20mA per led, we are talking a minimum of 200mA being drawn off a freshly charged hump pack. In 10 hours, this will run a 2000mA hump pack dry, and that’s a bit sucky tbh (yes, I know that the number of leds lit will reduce as the battery level drops but pffft :p)

To keep the design simple, it’s a 16F88 (chosen to protect my code, if this goes commercial) with the analog input connected to the battery terminals and an 8-led bar graph is displayed. I’m planning on having the unit display teh hump pack voltage for 30secs after power on, then permanently enter sleep until the next power cycle.

I just checked the datsheet, and during sleep this unit will draw a max of 0.6 to 5uA, which is ridiculously low. Seriously, this will not drain the battery, at all! You want to check the voltage again? As Acemastr has suggested, just flip the switch off, on quickly and it’ll display the voltage again.

Oh yea, due to the size of the BAT/GND pads, I left the decoupling cap out of the circuit as routing this PCB was proving to be tiresome - simply solder a cap of your choice across, i.e.a 10-100uF should do nicely.

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