Older 67 card readers and 65 card readers

[James Linder]

Tony, if I increase the resistor on the CRC board will it speed up or slow down the speed at which the cards are pulled through the calculator (motor speed)?

If you recall, the latest versions of the 67 used a variable resistor that could be adjusted using a tiny screw driver, however on the older units this would require replacing the fix sized resistor. I’m thinking HP used something close to a 4.6 K ohm resistor, so if I’d like to speed up the card reader what size resistor would I use? About 20% larger?

Is the key to speeding up the motor increasing the voltage for a constant current circuit as explained below?

A constant current source of 1 Ampere is connected to a 5 Ohm resistor, the voltage produced across the resistor is V = I * R = 1 * 5 = 5 Volts. If the same current source was connected to a 10 Ohm resistor the voltage produced across the resistor is V = I * R =1 * 10 = 10 Volts. Therefore, when a current in an electrical circuit is constant and if the resistance is increased the voltage will increase proportionally to the increase in resistance.