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HP-65 - 1605A02841 - Weird display behavior
02-12-2020, 05:20 AM (This post was last modified: 02-12-2020 05:21 AM by teenix.)
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teenix Offline
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RE: HP-65 - 1605A02841 - Weird display behavior
(02-11-2020 12:45 AM)teenix Wrote:  I don't think it was designed to provide 100% power to the motor, instead it will drive the motor with pulses to control the speed, and the resistor helps to set the pulse duty cycle.

It looks like the motor is not driven with PWM but more likely a constant current source to keep the speed steady.

Below is an oscilloscope trace of the HP-65 reading a card, showing the motor voltage (2V/div) and the lower one the voltage across the 4K64 trim resistor (0.2V/div). The resistor obviously sets the motor current.

cheers

Tony


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RE: HP-65 - 1605A02841 - Weird display behavior - teenix - 02-12-2020 05:20 AM



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