This is my target for the sensor stick:
- Runs at 3.3 volts using low quiescent regulator
- Uses an average current of 50uA
- Should run on battery for at least a year
At 50uA power usage and running for a year we need a battery that has: 50uAh*24hours*365years= 438mAh. So at least 438mAh is needed. Please note the battery internal drain, so we need more than calculated.
So here are my options
- 4x coin cell CR2032
- 6v
- 440mAh
- Small size, but consumes lot of space on PCB since it must be directly/flat attached to pcb
- 2x Double coin cell holders will cost 1.80euro @Digikey, BH800S
- Boost converter
- single cell from 1.5v would work (AAA)
- increased component/PCB cost, around 3 euro
- increased sleep current
- increased noise for the capacitance measurements
- Not an option due price tag.
- 3x AAA batteries
- 4.5volts
- 700mAh
- Alkaline cells has higher voltage drop in voltage curve than coin cells
- PCB mounts cost total 1.30 euro (BK-82 @digikey)
- Seperate AAA holder box cost around 50 eurocent @ebay
- 9v block
- 9volts
- 900mAh
- Higher voltage drop, just like AAA. But since it is 9 volts battery, we have a high margin.
- Consumes a lot of space.
- Battery snap-on wire cost 20 cent @ digikey
- Battery holder 60cents @ ebay or 1 euro @digikey
Putting all the things together, I currently think it is best to use the 9 volt block with snap-on wire.
