Voltmeter Clock Power Management on the ATtiny84

This is what it looks like:

This is what prototyping looks like at Awkward Engineer: Sometimes, kinda messy.

In previous posts, we went over chip selection, choosing a power source / battery (which we postponed until we could measure our system's current draw directly), and deciding to start BUILDING stuff.This past week, we ordered some parts off of Digikey and started breadboarding, which leads to our most recent activities, planning out our...

Software / Power Strategy

To truly take advantage of what the ATtiny84 microcontroller can do, we're going to be getting into some of the features of the chip that the Arduino environment normally hides. More specifically, we'll be taking advantage of some of the power saving modes.

As it turns out, the ATtiny84 has two timers that can be run completely independently of the actual CPU (plus a watchdog, which we won't use). The general idea, therefore, is to keep the CPU off as much as possible, saving power, and only doing work during periodic interrupt service routines when TIMER1 maxes out.

The first timer, TIMER0, will be used to control the PWM outputs that control the hands on the voltmeter. When initialized with the right settings, the timer will chug along independently of the CPU and the Output Compare Registers A & B will automatically compare their settings to the timer count, setting the duty cycle of the PWM outputs.

The second timer, TIMER1, has a 16 bit register that triggers an interrupt when it overflows, waking up the CPU. The microcontroller then polls the input to see if the "Mode select" knob has changed, adjusts the hands as appropriate, then goes back to sleep.

Here are some of our notes before we get deep into writing the software.

Marketing Cont...

This week, we tried checking out the Flea at MIT to drum up interest for the Voltmeter Clock and get more people signed up on our mailing list. In retrospect, it might not have been the best place to go (Shiny new gadgets are a bit out of place at what is essentially a garage sale for not so shiny, old gadgets), but we never would have known unless we tried and sometimes that's what entrepreneurship is about. I'll be keeping my eye out on some other events to go to, like Show & Tell Night at Artisan's Asylum in Somerville.

I generally find Facebook and social media marketing exhausting, so this week I tried scheduling posts for the first time. I'll see if this strategy is more maintainable / can be harnessed to drive signups to the email list.

Meanwhile, the email list is still growing through with targeted invitations, so we'll continue work on that front.

That's all for now!

Cheers!

-Sam aka The Awkward Engineer