Are there any pots inside?

I was watching my 9 year old daughter deftly manipulating the joystick on our original Sony PlayStation (predecessor of the Play Station 2) and that reminded me of a story.


I lived in Boston from 1976 to 1984. I liked to hang out in a surplus electronics store called Eli Heffron’s.. There were tons of old government electronics parts available for nary a buck. They must have salvaged old submarine parts from the Navy. There were huge racks of old sonar equipment, replete with vacuum tubes. Multiple floors of retired military electronics stuff gathering dust even in afterlife. Even today, ELI specializes in used Sun equipment.


I remember perusing a box of surplus joysticks, and was contemplating using them. I wiggled around the joystick and wondered if there were any potentiometers inside. Even today, you can turn over a mechanical computer mouse, remove the ball to clean it and see that the ball turns 2 potentiometers inside: one each for detecting X and Y motion. A potentiometer is typically an electro-mechanical device that has an axis that can rotate to vary the electrical resistance in a circuit: just like a radio volume knob. So, indicating the joystick, I asked the sales clerk: “Are there any pots inside?”


The clerk gave a wry look back at me. After a moment of thought, he responded “Of course there are pots inside!”


I distinctly remember feeling that he didn’t have any idea what I was talking about, and that he probably thought the same thing about me. Remember: Eli’s was in East Cambridge, and many of the locals had a heavy accent. Think “I paahked my caah in hahvahd yahd” (I parked my car in Harvard Yard). I eventually figured out he thought I asked “Are there any ‘paahts’ inside?” as in “parts”. No wonder the quizzical look! I eventually bought a digital joystick, which had 4 buttons: indicating whether the user pushed the stick North, South, East, or West, or perhaps NorthEast.


I had built a Heathkit 25 inch color TV. For those who don’t know, Heathkit sold kits that were “housewife tested”: bags of electronic parts and instructions on how to solder them together. I made a Heathkit stereo, oscilloscope, TV and learned a lot about electronics.


I remember finding some static RAM modules: I believe they were 1K bits each, and I bought 4 of them. Because they were static, they could remember their contents with no refresh circuitry needed. The father of a friend of mine worked at Bell Labs in New Jersey, and he was able to get us video speed A/D and D/A converters (digital/analog). These were amazingly expensive at the time: being able to digitize baseband analog TV signals at 6 Megahertz. They were also huge: the D/A was about the size of a small paperback, the A/D was about 3 times larger. I was able to rig these up to my Heathkit TV, so I could digitize the incoming video, modify it at will, then pass it back through the D/A to the TV. I had my own digital special effects generator! I could invert the signal to show the negative image. I could take all pixels above a particular threshold value and invert them. I could draw images with my new joystick.


I also had a light sensing diode, which I could attach to a pen and it point it at the TV. As the horizontal retrace of the TV swept by, the diode could sense the light and send an electronic signal to the static RAMs.


I was able to draw images on live TV in 1982: way before the football guys could draw X’s and O’s on the screen to indicate which way the players go. I could draw a mustache on the weatherman’s face!


In the 80’s, while living in Honolulu, I used to love going to California to ski at Tahoe and visit Fry’s electronics in Santa Clara. Again, there were tons of electronic parts available. A quick check on the website indicates that it’s the same Fry’s electronics store available today in Renton.


See also Why was the original IBM PC 4.77 Megahertz?

Comments (6)
  1. wOOdy says:

    I question that any mechanical mouse had potentiometers inside! Remember: a "pot" uses a resistor plate on which you move the pinpoint for a maximum degree of sy 270°. So how would you transpose an ongoing motion to a limited 270° angle?  As far as I remember, even the early mice had optical sensors, which just counted the x and y movements.

    But Joysticks had potentiometers, that have been the "analog devices", whereas the first "digital Joysticks"  simply had four switches.

  2. Maros Klempa says:

    Hello Calvin, sorry for off-topic question. I want ask you how report bug in VFP9SP1. Is there a e-mail address? I have small piece of code which allways send VFP to C000005.


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