I’ve separated the Switec X25 motor driver code into a separate library repository on GitHub. This will make it easier to use the driver library in other applications.

I’ve been looking around on-line and in stores for some parts to make some classy steam-punk gauges. After a lot of searching I came across Lets Make Time here in Australia who carry clock and weather station parts at very reasonable prices. It’s always hard to gauge build quality from pictures, so I laid down some cash and bought a grab bag of stuff. The order arrived and it all looks great. It was no surprise to find the rectangular gauges are made from plastic and look a bit cheap, but I really love the retro shape and they actually don’t look too bad. I haven’t cut one open yet, but from the outside everything looks great for my purposes.

The logic in the advance() function of the Switec X25 library steps the motor forward or backward one step, then computes the delay in microseconds until the next step is due. This logic determines the acceleration curve and maximum speed of the needle. My first cut at this code used floating point arithmetic to model this as time/accel/velocity problem. The motion was nice and smooth, but it was overkill, and consumes too many precious Arduino compute cycles. When driving multiple motors, this will create an artificial ceiling on the maximum motor speed. I’ve rewritten that logic to use a simple lookup table instead. This is a fairly obvious approach, but it was reassuring to see similar approaches recommended in both the VID 29 documentation and the MCR MR1107 data sheet .