HP-35 and HP-65 Current Requirements



#2

Hello all,

I got bored in the lab today, and I was thinking of the wikipedia article on the HP-35. It says that users would press the decimal point key to save the battery (and the on/off switch).

I got to thinking just how much battery this would really save, so I figured I'd do some current measuring and share the results with you.

-------------------------HP-35------------------

Display----------Current in DC milliamperes

.--------------------79

0.-------------------84

88.------------------88

888.-----------------91

8888.---------------95

88888.--------------98

888888.------------102

8888888.-----------106

88888888.----------109

888888888.---------113

8888888888.-------116

-8888888888.-88--125

So, assuming you have a 1000 mAh battery,
1000 mAh ÷ 84 mA = 11.90 hours

If you press the decimal point,
1000 mAh ÷ 79 mA = 12.66 hours

Now for the HP-65,

----------------------HP-65--------------------

Display----------Current in DC milliamperes

.-------------------133

0.00----------------142

8.------------------137

88.-----------------141

888.---------------144

8888.--------------148

88888.-------------152

888888.------------155

8888888.----------159

88888888.---------163

888888888.--------167

8888888888.-------171

-8888888888.-88--179

I knew the deciding factor on run time was how many cards I passed through the machine, so I decided to try that next.

I fed a card in (with the ammeter set to capture and hold the biggest value it encountered) 4 times.

Trial-----Current in DC milliamperes

1---------258

2---------302

3---------307

4---------392

It should be noted that these trials were done in quick succession. This means I put the card back through immediately after it came out the other side. I'm unsure if this has anything to do with the results, however.

I took the meter off its MAX function and fed the card a couple more times, averaging about 295 mA.

So, if we were to (somehow) run the motor constantly (probably not a good idea):

2000 mAh ÷ 295 mA = 8.51 hours

which is significantly shorter than illuminating just the decimal point:

2000 mAh ÷ 133 mA = 15.04 hours.

I hope you learned something from the results and I encourage you to come up with your own.

-Dan


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