A MOSFET Current Mirror
This is a little MOSFET current mirror I threw together to subvert the tyranny of I2R. I recall that I used it to limit charging current to a small supercapacitor. There's nothing fancy about it -- however I like how the hand soldering worked out. It's a cute little thing.
A Tilt-Activated Night Light
This is a very simple circuit. An Attiny10 microcontroller wakes from sleep when a tilt switch triggers. If you keep it upside-down long enough (a few seconds), it will light up an LED (or trigger an optional MOSFET). After 30 minutes, or if you repeat the tilt action, it will turn off.
The goal was to make something lovely to help children who have trouble falling asleep in the dark. A single CR2032 powers the device for a long time. The deep sleep mode of the Attiny10 is used without the WDT active, so power consumption is just a little over 100 nanoamperes when inactive.
The auto-power off means it won't run all night. The fact that you turn it upside down to turn it on, makes it easy to use, even in the dark. The biggest issue was that tilt switches tend to be sort of tall compared to the rest of the circuit. I tried getting some smaller ones, but reliability was so-so.
The circuit is very small, so I crammed it in to a tiny case and added a cute rubber duck:
A Low-Voltage Tube Amp
I heard that it was possible (although impractical) to use certain vacuum tubes at very low voltages. One day I found a vacuum tube in a corner of a used bookshop, in a junk section. Predictably, this was while visiting Japan. The staff warned me that it was not guaranteed to work -- sounds like fun!
So, I tried to get it to amplify at only 5V. The filament glowed a healthy orange, and... it worked! Sort of. With acutely distressing distortion, and very high output impedance. So I shoved a Chinese amplifier module that I lost the datasheet for in front of it. As intended, that made it even worse. I called it a roaring success (and indeed, it converts singing to roaring).
I also added some lithium cells and so on. Oh, and also the mandatory military-specification output filter capacitor from the USSR. It's perhaps best classified as a lithium-powered pocket warmer with inexplicable audio functions. Just what I need in the tropics!
A PS/2 to TTL Serial Converter
As a small part of [redacted] I needed a way to convert PS/2 keyboard signals to TTL serial output. Like, for example when you want to send commands manually to some MCU. But don't need a screen, and don't have a laptop for some reason? Frankly, I've forgotten what I was thinking when I built this, which is probably for the best.
It works well enough though, and looks pretty!
