Wednesday, May 17, 2006
Magnetic Shaft Encoders
Vik has been rabbiting on about the magnetic rotary encoder chips from Austria Microsystems for ages, and so I finally got round to trying them out.
Guess what? They are beaut!
I rapid prototyped a holder for a small piece of stripboard to go on the back of one of the geared motors that I used for the Mark II Extruder, soldered one to the board, and put the lot together:
A small magnet is mounted on the motor's shaft, and Hall-effect probes in the chip encode the rotating magnetic field. Here's the scope trace:
There are two outputs which give quadrature (i.e. the phase tells you if the thing is going clockwise or anticlockwise).
I used the chip that gives 256 steps per revolution (the AS5035), but they go up to 4096. The signal is clean reliable and easy to feed into a PIC. And the circuit is simplicity itself (though it needs to be soldered by ants, as the chip is SMT).
For more details, see the Wiki here.
I don't think I'm lucky. I think they designed it right.
Yup - that's how I did it. Useful tips: you need a big magnifying glass, or some half-round bottle-end old-person's reading glasses from the chemist (mine cost £12, and you can stick them on the end of your nose like a librarian...); Hold the soldering iron together with a light rigid stick about 300 mm long that you can rest on the bench to steady your hand - just like those sticks with a pad on the end that you see art restorers using; and finally drink no beer the night before...