I'm hoping to power an ATtiny85V for a nice long time on some small battery, probably a coin cell.
I've looked into the software side, and my code is watchdog timer driven, has unused analog and digital converters turned off, the chip is running at 1MHz etc. Of course being both busy and new at this, I'm not sure exactly how much current it is drawing, but I'm hoping I have basically minimized it.
Every few seconds it wakes up, does its voltage level checks on the ADCs, records it to ram, and goes back to sleep. If it detects a serial line is connected, it spews the data out.
However, now I'm looking at the circuit as a whole and wondering if there are things I should do to make the circuit as a whole more battery friendly?
What are the basic dos and don'ts when it comes to designing a long lasting (simple) circuit where one component (the microcontroller) has a repetitive but variable current draw?
- Is an indicator LED a big deal? Is it using up the battery when it is bright? Should I put a giant resistor on it to make it dim, or does that just make the resistor use the battery?
- Should I use bypass/decoupling capacitors to even out the current draw from the battery, or will the capacitor just waste the battery's power?
- The microcontroller only needs 1.8V, but I don't have any 1.8V batteries. Should I use two 1.x batteries and send it too much voltage? Can I prolong the battery life by "not using as many volts"? How do I do that?
- Does it take extra power to check if a pin is HIGH or LOW? Like compared to a no-op or some arithmetic, is there much additional power usage in checking one of the GP I/O pins for its state?
I vaguely know how to compute (and more vaguely how to measure) current, voltage, power, but I'm not really sure which of those things equates to battery life. Is the important measurement of battery life in Coulombs?
I have this vague idea that batteries are full of stuff like:
- charge, as in amp-hours
- energy, as in watt-hours
- power, as in watts
but I am not really clear on what my circuit "eats" when it runs. I've read a fair amount of EE101 and physics textbooks, but I don't really have any lab experience. In other words, I've read a ton about batteries, but I'm not really sure what most of it means in practice.
Do resistors use up battery life? Do capacitors? Do diodes? I suspect they all do, but which of the numbers are the ones that matter? Impedance? Power dissipation? Current? Voltage?
Is there a way to lower voltage without wasting battery? Is there a way to lower voltage while increasing battery life?