ther Pages of Rages

Thanks to Chris, the builder of stuff, who prepared this rendering of the scanner for me:

Well, I’m gonna be going to the Amia conference in Anchorage, Alaska next week.

I want to take my second prototype film scanner to show it in at a vendor booth. One problem: I don’t have one yet! All the parts should arrive this week. So I’ll be working day and night to get it together.

I’m excited about the new design. The ripple in the last test film is caused by two things: First, the brush-DC motors I was using had some “cogging” as the motor turned. This was preventing the film from moving smoothly through the transport. Secondly, the displacement sensor I was using (the carcass of an optical mouse), which *should* have canceled out the motion, has a lowly 300 dpi resolution. I made a PLL to translate this signal up to the line clock for the camera, but the sensor resolution limited the accuracy of the line clock.

After some interesting but ugly work with a stepper motor (too many moving parts), I switched to a high-torque pancake motor directly driving the spindles. Much better. This motor has no cogging that I can feel, and turns very smoothly. If this was a money-no-object design, I would use e-TORQ motors. But, remembering the 80/20 rule, I found a Chinese manufacturer of decent pancake motors intended for electric bicycle use. I designed a current-mode controller for them. I’ll have to limit their maximum speed: They can really whip a reel of film around! Maybe this can be a feature: rewind 800 feet of film in twenty seconds!

I’m also going to replace the 300 dpi sensor with a new 1600 dpi sensor (sacrificed from a Razer mouse). This should give a good, stable image. Thanks to HP/Agilent/Avago for putting their excellent datasheets online.

It’s exciting to see something come together after working for almost a year on it.