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The Casio CP-10 is a neat calculator that has a thermal printer attached. The calculator also has a built-in clock and can do useful tasks such as printing this month’s calendar. The date rang eis also useful as it ends in 2099. The printer is a small mechanism that take standard 38mm thermal paper. I found out that the mechanism is the same one that the FP-12 printer uses. This is a small printer that is designed to attach to a variety of calculators and pocket computers.

I bought a CP-10 to see if I could re-use the printer mechanism instead of the receipt printers that I have bought off ebay in the past. They are relatively expensive (over £20) whereas the CP-10 can be had for half the price, if the CP-10 is listed as non-working. Unfortunately the CP-10 has a NiCd battery pack, as the printer mechanism take a fair current when running and the pack is used to supply that. This means that a lot of CP-10s have suffered battery leakage and failed. This is what had happened to my example. After a brief attempt to revive it I cut off the printer mechanism and attached a blue pill and some extra circuitry.

There’s seven transistors, one for each thermal element, and one transistor that drives the motor. There’s an input for the home position switch as well. The mechanism has a tachometer output that gives a series of pulses as a magnet rotates near a coil. The magnet is attached to the motor, so this arrangement gives a reading of the motor speed. The pulse may also be used for dot timing. Unfortunately my mechanism seems to have a broken tachometer output. The coil reads 25M resistance, which is a bit high for a coil of wire. (I have since bought a second CP-10, this one shows signs of life and its coil reads 82R, so is much healthier). After trying my own tacho circuit, then copying the CP-10 circuit, then building a higher gain circuit with an op-amp I decided that the tacho output wasn’t reliable enough to use. This may not be too much of a problem if the motor is run off a stable supply as the speed of the motor should be fixed. I should be able to time the motor moving from home position back to home position and scale the dot timings appropriately if need be.”

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