On Looking into Mouse Sensors

Posted in Arduino, Computer Vision, Electronics, Making, Reverse Engineering - October 1, 2019 - 0 Comment

That is to say, the sensors from optical mice, rather than a sensor intended to detect the small rodent.

I have 10 boards from optical mice and three desoldered sensors. Among that bunch there are two common IC packages, a 16-pin staggered DIP (4 units) and an 8-pin staggered DIP (6 units). There is also a 20-pin staggered DIP, and two 12-pin DIP packages.

Most of the chips were made by Agilent, or Avago, a spin-off of Agilent that eventually bought Broadcom and started operating under that name. A couple are from At Lab, or as they style themselves “@lab”.

The chip interfaces are very heterogeneous. Some of them just output PS2 data and clock signals, and so are a very integrated mouse IC. Some of them output quadrature signals for x and y motion.

I had high hopes for using these mouse sensors for a couple of hacks. One of them is that they are essentially optical flow processors, so you can use them to either get velocity based on the observed motion of stationary objects from a moving platform, assuming you know how far away the objects are (and so get odometry for a moving robot by watching the ground roll by). The inverse of that is that you can also get how far away an object is assuming that it is stationary and you know your own speed (for height over ground detection in a drone, for example).

Ultimately, though, I don’t think this stash of ICs is going to do the job I want. What I want is something I can drop into projects I’m working on, and reverse engineering each of these, finding the datasheets for ICs old enough to support PS2 protocol, and so forth, would be its own hassle of a project. USB optical mice are $7 or so, so I can’t really justify the effort to get these working, sort out optics for them, etc.

On top of that, drone optical flow sensors with the optics already sorted are like $10-20, so for that use case, I can just buy the part. For robot odometry, I can use the same part, or put optics on a USB mouse that can actually plug into a recent computer, instead of decoding quadrature or PS2.

It feels kind of weird to pick up one of my old projects that I had been kind of looking forward to, and realize that it’s simply not useful or interesting, but I guess that’s just how it goes. At least I can free up that parts drawer now!