Making Things Cheap

In the last post I sketched out an idea for the project I’d like to work on this term. Here I summarise some technical research I’ve conducted to follow up and start costing a prototype.

Microcontrollers

Choice of microcontroller is a key decision. The program for each module will probably be extremely simple (depending on whether modules communicate or not).

Requirements:

• Arduino compatible (ideally - for the sake of ease)
• Able to run a simple metronomic program to trigger solenoids in patterns
• Only needs one pin
• Takes external power

I researched several options, and by the far the most hopeful is the Attiny85. It’s extremely cheap and looks like it will do everything I need it to. It doesn’t have many pins, but I will not need many.

Some Attiny85 resources:

• Digispark Attiny85 Micro Arduino 5V Development Board
• Digispark Attiny85 documentation
• An Introduction to the Attiny85

Solenoids

It will be important to use 5V solenoids instead of the 9V ones I used on the Autoreong, so only one power source will be required.

Using 5V will simplify the circuit. A simple circuit design would use:

• 1 x 5V solenoid
• 1 x 220 ohm resistor
• 1 x 1N4004 diode
• 1 x NPN (BC547) transistor

Some of the cheaper 5V solenoids I found:

• DC Solenoid Electromagnet - SODIAL(R)DC 4.5V 40g/2mm Open Frame Actuator Push Pull Solenoid Electromagnet
• DC 5V 1.1A Pull Type 5mm Stroke 50GF Force Solenoid Electromagnet

Power

The circuit will need to be powered by a battery, but both battery life and size will be important factors. This will require some experimentation. I’m interested in exploring alkaline batteries, as they can potentially provide power for a very long time and tend to look a bit nicer than regular batteries (this is important since the aesthetic of the modules is all about exposed circuitry). Resources on using alkaline batteries with microcontrollers was hard to come by, but what I did find suggests it’s possible:

• Reddit: power an arduino uno with 4 aa alkaline batteries

Conclusion

As a rough estimate it looks like I should be able to put together a basic module prototype for somewhere in the region of £10. As a starting point this is less than I was expecting, and gives me some confidence that this is a viable project. I’ve ordered some of these components - once they’ve arrived I can start building some circuits.