HP 67 battery charger

[Paul Davis]

Can anyone provide a specification or circuit diagram for building a battery charger for the HP67?

Many thanks,

-Paul

[DaveC]

I'd actually buy an existing stabalised supplyand change that. The only additional component you need is a current limit resistor and a power diode. The important operating voltage is that that runs the calculator which needs to be set accurately at 3.75 to 4 volts. The additional diode and resistor can be used to form a charging circuit direct from the secondary of the transformer. I'd choose the resistor to pass C/10 to C/15. (C=Capacity of cell).

[DaveC]

Also see http://www.hpmuseum.org/batts/battery.htm