I was looking at which of the AVR Tiny microcontrollers was best to experiment with, and thought that the ATtiny3217 looked promising. It's not the simplest or cheapest, but the 24-pin VQFN it's packaged in is only 4mm across, so is physically smaller than the 8-pin SOIC of some of the other Tiny devices, and allows a lot more to be done. You can buy them for less than £1 each fairly easily, and about 65p if you're willing to buy more (500!)
Admittedly, a part that small is going to be a pain to hand solder, but I can probably do it carefully, and can possibly also get it assembled commercially for not a lot of money, when having a PCB made.
I searched for a way to easily experiment with it, and looking for development boards originally found the
Dily 3217, but that doesn't seem to be sold by anyone. Luckily, after a little more hunting I found the
ATtiny3217 Nano Curiosity board on Microchip's website, for only £11 each!
Like a lot of DIL boards, such as the Teensys and Arduino Nanos, it's meant to be plugged into a breadboard, but also has support for some development options such as controlling the regulator voltage and programming the board over the USB connector.
Reading the
datasheet for the ATtiny3217, it's actually a remarkably powerful AVR device. There are a lot of cheap Cortex-M0+ devices on the market now, but this AVR one is likely to be less power-hungry. I think you can use every one of the 22 non-power pins for IO, it can run using its internal 20MHz (or 16MHz) oscillator, has 32kBytes of Flash, 2kBytes of RAM and 256 bytes of EEPROM, a USART, SPI and I2C interfaces, an ADC, DAC and PWM, not to mention some of the really complicated stuff!
Experimenting with it should be fun, yes I know I'm weird.