HP-41CL & TIME module (extending time keeping)


Hi all,

Some of the CL users out there that want to have the TIME functions handy (I know of a number of them), will have eventually noticed that the TIME module is prone to loose its contents a few secon after the CL has been disconnected from a power source.

A standard HP-41 can keep the time for some 2'30" or 3 minutes just using its internal capacitor (470 uF).

Due to its internal design, CL's cannot hold charge enough in its caps to keep the TIME module running more than 15 or 20 seconds, which is a very tight gap if you need to replace a set of alkalines.

I'm not a SW guy, but like to have my clocks on time, so when it comes to fit a TIME module into my CL I included a small capacitor (220 uF 6.3v) PC CON type.

To avoid the capacitor being discharged thru the NEWT board, a diode is inserted in the module's power line.

As a result, the time is kept for about 1'45", good enough to replace batteries or find any other suitable power source.

Some pics my help with the details:

The TIME module disassembled and pre-wired.

The added capacitor.

And the TIME module in its new place.

Hope this can be useful for someone.

Merry Christmas!!



Excellent job and your soldering skills are exquisite.

I will be hardwiring to my system also.

Cheers, Geoff


Thanks for your kind words Geoff, same can be said on your restoration skills... :-)

Merry Christmas and all the best from the Canary Islands.


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