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I built a special dialysate proportioning system for Drake-Willock, another manufacturer of kidney machines doing business in Oregon. I was working alone, from home. The proportioning system was a compact aggregate of three separate switching power supplies. It had analog servo circuits to control the output of the power supplies so that the loads, in this case three peristaltic pumps, maintained a fixed delivery rate ratio at any speed within the specified range. The speed encoders were disks perforated at the periphery at regular intervals. With pulleys, springs and piano wire I jury-rigged three Prony brakes to measure torque and power outputs.

     Peristaltic pumps work by squeezing tubing through which a liquid
     (typically blood) is flowing. The idea is to avoid contaminating the 
     liquid. The torque required for driving the rollers is large and 
     uneven, with an elastic component. Servo control can be a problem.

During that year I also experimented with a mobility aid for the blind. It featured retina optics that could be aimed at any object and would return audible signals describing linear features and colors.

The device -- a wand with an 8mm movie camera lens at the end linked by a fiber-optic cable to a small portable case -- impressed Lawrence Scadden, a blind man in charge of technological aids for the blind at the Smith-Kettlewell Institute in San Francisco. The poor man almost got run over by a car because he was so absorbed "listening" to the white line at a pedestrian crossing. A potential investor refused to invest in the project because someone had already patented the basic idea (but in a much more primitive embodiment).