04-18-1999, 09:28 AM
04-18-1999, 05:13 PM
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).
04-18-1999, 05:14 PM
Also see http://www.hpmuseum.org/batts/battery.htm