Resistor Ink

Discussion in 'Request a Feature' started by Steve Payor, Apr 30, 2015.

  1. About 40 years ago I made a PCB with stick-on foil tracks, and painted the resistors between the pads with a camel-hair brush, and ink made from graphite powder and diluted (water based) PVA adhesive as a binder. (I was lucky with the paint mix, because the resistance was almost the same wet and dry, so I could use a multimeter to check the resistance as it was being painted.)
    The resistors were about as stable as most carbon film resistors from the 1950's. Good enough for logic, oscillators etc. but not quite good enough for precision analog circuits. Values from 1k to 1M were easily painted, and the circuit still works now. The frequency of the R-C oscillator on board is still about the same.
    (Capacitors up to .01uF were made by painting layers of clear, solvent-resistant lacquer between layers of spray-can conductive nickel paint.)
    Another application for resistive tracks with high impedance is electrostatic speakers. Here the resistance needs to be in the hundreds of Mohms, for which ordinary, carbon-black, water based drawing ink is ideal.
  2. Ariel

    Ariel Staff Member

    That super cool that you were able to paint on the resistors accurately enough. I'd love to see a photo of the circuit if you still have it around.

    Resistive ink is definitely something we're actively seeking (along with dozens of other things, mostly novel inks) and using a carbon based ink is a good idea for that. We have been operating under the assumption that we should be able to get the silver deposition accurate enough to print resistors with repeatable resistance, but the problem is that so little silver is required there are problems with heat dissipation. Carbon would probably clear that up.

    I'll add it to the testing list! ;)

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