Driver

Finally my stepper driver arrived. Now I don't need to use my own home-grown driver circuit.

The benefits are: DIP-switch controllable current (up to 4.2A, my own circuit only does up to 1.5A) and sub-stepping up to ludicrous levels (using Allegro A3955 I get only down to 1/8 steps). And it's very easy to use. Just plug it in and it does its work. I just have two pins to worry about - direction and pulse. It steps the stepper itself. The downside of course the price.

Unfortunately the speed I hoped for did not really materialize. If only slightly. Currently I'm unsure if it can keep up with what the HP control circuit expects. If not - need to get a better stepper motor. But that's easy - just need to plug it in, driver takes care of the rest.

And on another note I found out why my printer got paper jam errors. The contraption to move the sensor was just not fast enough. I down-geared it by around ~1:4.45 because the encoder wheel has 1200 dashes while my stepper does 400 steps. Instead I should have relied on sub-stepping the motor and attached the encoder directly. If I overdrive the motor I can almost get it to work. It even started scrolling out the paper when the paper sensor was on. But its checking systems move it forw-back very sharply and the stepper tends to jam on that.

I don't feel like rebuilding the stepper thingie right now so am instead reverting to reverse-engineering the sensor. I've already attached wires to it and it seems to indeed be a two-channel system. Though I haven't really got the sense of all the pins, only two of them seem to have any sensible life in them as can be seen on the following picture:

As you can see the green leads the yellow - two channels being covered by the encoder strip as it moves.