HP Forums

Full Version: 82104A card reader current measurements?
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

Does anyone happen to have measurements of the current consumption of the card reader while reading or writing a card? Or the total of the 41 and card reader?

I only recall a measurement of the motor alone, between 7 and 9mA.


I think you can hook up a regulated DC power supply with a DC ammeter in series to the battery terminals to do this. I have done this with a number of calculators, although never with one that included a card reader. You have peaked my interest so maybe I'll try it with one of card reader calcs (HP65/HP67/HP97). I own two HP41CV's but no card reader. I think they all use the same DC card reader motor, so I'd expect comparable current draw.


Yes, I could measure it myself, if I had a card reader. I don't, and thus the request.

Here's some preliminary info based on a HP65:

Applied voltage at battery terminals - 3.75 Vdc

1) Calculator powered on and idle - display 0.00 - 140 mA

2) Calculator during a card read - 300 mA

3) Net current draw of card reader = 160 mA

Note that the current draw initially peaks as high as 450 mA as the motor does extra work grabbing the card and overcoming initial static friction (sliding friction is less). Also, I imagine this will vary between different card readers based on the tightness of the drive roller. If you are interested, I will test other calculators as I have 3 HP65's, 2 HP67s and a HP97. Also, all of these have been refurbished, so I have no baseline to the original.

Edited: 10 June 2009, 6:02 p.m.

Found the information in the archives, while looking for something else. Summary: 150-200mA continuous (while in operation), with peak current of up to 1A.


Thanks for taking those measurements. I'm assuming that the HP-67 measurements will probably be similar, and that will help with another one of my mad scientist projects that I hope to show off at HHC 2010. (I've got a different mad scientist project in the works that I hope to show at HHC 2009.)

Seems consistent with my results.