Moding Card Reader for 5V Power

[teenix]

I don't know much about the 41. I have a dead one so not much help.

I guess with 4 x NiCad cells the battery supply would be around 5V which is probably why the USB power idea. I am not sure if this will work properly because of the high current demands when the motor turns on. The external power supply is probably a better option.

As the motor drive is probably the power-hungry part of the 41 card reader, then one simple idea would be opening the connection to the motor driver transistor (collector pin) where it connects to the +ve battery supply. Then use the external supply +ve only to that collector connection. This would supply the motor with an external power source, and of course you need a ground connection as well.

I don't know if the battery +ve at the motor is switched on or off from the calculator power enable, or it is live all the time. If it is switched, then you could construct a simple circuit to monitor the (now open circuited) battery +ve to enable the motor power from the external supply.

cheers

Tony