Drained batteries, LEDs, and creative solitude

(April 2020)

It was just after the 3rd week of complete isolation due to COVID-19, that I noticed a drained AA battery, sitting in a corner.

"Poor thing. Are you feeling as useless as I am?"

I took my multimeter, and measured it - yep, down to 0.8V. Far lower than the nominal 1.5V - no wonder it couldn't power the device.

"Bin material... You can't drive anything, not even an LED..."

No juice left. Or is there?

Wait a second. Voltage can be boosted, can't it? If so, it can drive an LED.

Looking at my drawers. Dust, cough, dust.

There!

Boost me up

I bought these boost converters, alongside many other electronics parts, when I immigrated. Don't judge - a man needs a hobby, and this is a really rewarding one. I've had tons of fun with electronics.

But after reading the specs...

"Input voltage: 2V-24V."

Damn.

Research, phase 1

Let's Google.

A couple of hours later, and I've read all about the Joule Thief.

In the video above, Clive Mitchell - affectionately known as "Big Clive" to his Youtube subscribers - builds his improved design, specifically made to "steal" the last ounce of energy out of a dead battery.

But his design depends on an inductor. I don't have any - nor do I have any ferrite core to wrap some wire around. I could, probably, still wing one; but somehow, I want to deviate.

Is there a way to boost voltage without an inductor?

Research, phase 2

Ah, there's also a family of designs, that are called charge pumps. These only depend on diodes and capacitors! I have both of these handy...

Dave Jones - another famous electronics Youtuber - shows how these work:

OK, this is becoming exciting.

All I need to do, is to create a clock, pulsing at a frequency of at least 100Hz - and arrange pairs of Schottky diodes and capacitors. The voltage will go up!

But... wait a second.

I can't power any of my microcontrollers with 0.8V. My Arduinos need at least 5V; even the pro mini versions need 3.3V, just like the ESP8266 and the STM32F1s that I have.

Argh. How can I create a pulse from 0.8V, without a microcontroller?

Down to basics

Well, one of the things I stumbled on, as I spent time on this hobby over the last 4 years, was the astable multivibrator; a design that uses only resistors, capacitors, and transistors, to create never-ending oscillations from an input voltage. As long as the voltage is high enough to turn a transistor on, this should work.

Well, 0.8V is larger than 0.65V. And I do have a box with transistors.

(heartbeat elevates)

Since I am a complete idiot in everything electronics related, my only salvation is to simulate first.

I launch LTSpice, and create this design: