DM-41 firmware V17

[Sadsilence]

As a great HP41 fan I could not resist for a long time before buying a DM-41. First I was a little bit disappointed cause of keyboard. Now I completely changed my mind. Of course keys are a compromise, but in all other parts it is great.

With HP41 timer completely implemented you can use it as a(n) (alarm) clock and stuff like that. With DM-41 I eventually found a reliable method for checking button cell rechargable batteries, which I use in some other devices. Rechargeable button cells do not suffer so much from high internal resistance when current load is constantly in mA range like described here. Unfortunately you cannot use racing car chargers for charging/capacity check. Normally charge/discharge current starts at 50/100 mA for such chargers which is much too high for button cells. There are a few simple button cell chargers available, that do a reasonable job (normally after modifying too high charge current);alone discharge option with capacity check is not there.

DM-41 current load is nearly constant @ 4.2 mA when keeping it busy @ 12 MHz and 13.5 mA when keeping it busy @ 48 MHz and running it with a 3.6/3.7V rechargeable button cell. Together with "Akkutest" program rechargable button cells not only are discharged at a reasonable current level but integrated stopwatch automatically measures discharge time. Moreover program switches off calculator when battery nearly empty flag is set, preventing deep discharge of battery (and a memory lost). You can even use stored stopwatch value to calculate battery capacity by multiply it with current values mentioned above ;-). Perfect. For that purpose I modified DM-41 a little bit, so I can attach button cells of different size.

Best regards,

Werner