Moding Card Reader for 5V Power

[TallKey]

Considering modifying a card reader for powering my 41.
Looks doable, but perhaps I have misunderstood the schematics.

Power source would is a USB 5V AC adapter/PC USB port (like the below link).


Conditions:
1 - Haven't a module to modify
2 - Have a CR in need of repair*

To reiterate, while I have the CR apart for repair, what reason would you refrain from modifying the CR for powering the 41 (see above link)?

The CR in-hand has the gummy wheel problem.

*The CR uses a lot of current, for those who have no experience with a card reader, more current than any peripheral I am aware of for the 41.

[cdmackay]

see also: https://www.hpmuseum.org/forum/thread-19...#pid173046

[TallKey]

(05-21-2023 08:09 PM)cdmackay Wrote:  see also: https://www.hpmuseum.org/forum/thread-19...#pid173046

100% not what I am asking. Thanks.

[cdmackay]

(05-21-2023 08:54 PM)TallKey Wrote:  100% not what I am asking. Thanks.

Yes, I know, which is why I said see also, as I thought you might also be interested in alternative power arrangements.

[TallKey]

(05-21-2023 10:21 PM)cdmackay Wrote:  

(05-21-2023 08:54 PM)TallKey Wrote:  100% not what I am asking. Thanks.

Yes, I know, which is why I said see also, as I thought you might also be interested in alternative power arrangements.

Being I am the OP in that thread, I have no interest in rereading it.

What I am interested is a discussion about what is suggested in post #1 here.

Thanks

[teenix]

I don't know much about the 41. I have a dead one so not much help.

I guess with 4 x NiCad cells the battery supply would be around 5V which is probably why the USB power idea. I am not sure if this will work properly because of the high current demands when the motor turns on. The external power supply is probably a better option.

As the motor drive is probably the power-hungry part of the 41 card reader, then one simple idea would be opening the connection to the motor driver transistor (collector pin) where it connects to the +ve battery supply. Then use the external supply +ve only to that collector connection. This would supply the motor with an external power source, and of course you need a ground connection as well.

I don't know if the battery +ve at the motor is switched on or off from the calculator power enable, or it is live all the time. If it is switched, then you could construct a simple circuit to monitor the (now open circuited) battery +ve to enable the motor power from the external supply.

cheers

Tony

[TallKey]

Tony, you raise good questions. See this thread. Same link as post #1.

CR runs 4.4V to 5.5V, per CR service manual, p4-4 and can pull voltage down to 3.4V (as I read the SM).

Net is this:
Power 41 with external power.
Repair a broken CR.
While repairing broken CR perform what is suggested in the above post.

Below is the meat and potato part of the above link:
As long as you have a USB port handy (any stable power source for that matter)

Standard USB cable
- Cut the cable to an appropriate length.
- Identify the +ve and -ve wires.
- Solder the Positive wire to BAT
- Solder the Negative wire to GND

Disinterested in sacrificing a 41 module or squander a 41 port. That is ought to be clear from post #1.

[mfleming]

(05-21-2023 07:07 PM)TallKey Wrote:  To reiterate, while I have the CR apart for repair, what reason would you refrain from modifying the CR for powering the 41 (see above link)?

a) The 41 would be tethered to the point the USB supply is powered; motion limited by length of cable,
b) Memory Lost when cable or CR disconnected

My take, anyway. Might add accidentally frying the works to the list too.

[Diego Diaz]

Hi again,

(05-21-2023 07:07 PM)TallKey Wrote:  To reiterate, while I have the CR apart for repair, what reason would you refrain from modifying the CR for powering the 41 (see above link)?

The CR in-hand has the gummy wheel problem.

*The CR uses a lot of current, for those who have no experience with a card reader, more current than any peripheral I am aware of for the 41.

Certainly I don't find any reason to refrain you in attempting this mod to your card reader once you've fixed the gummy wheel problem.

This will also have the advantage of removing the CR extra current from the I/O BAT connector.

Do you plan to include a connector for the USB power in the CR, or a pass-thru cable permanetly attached?

Please share some pics if/when available.

Cheers.

Diego.

[TallKey]

(05-22-2023 06:50 PM)Diego Diaz Wrote:  Hi again,

Do you plan to include a connector for the USB power in the CR, or a pass-thru cable permanetly attached?

Please share some pics if/when available.

Cheers.

Diego.

Sizing up USB DIP packages. Many choices to consider, small and sans PCB seems the better choice.

Too have to evaluate my plastic milling skills and decide on a secure connector attachment method. Epoxy or a fastener attached charging port, unsure which attachment route I will go.

Hard-wiring a cable, that'd be easy!

[John Garza (3665)]

Maybe I missed something, but this looks like a proposed solution to an as yet unstated problem.

What's the problem?

What I can glean from the convos is a high current drain with the motor. Uh.. yeah. It's a motor. If you use the card reader a lot it would drain the batteries faster. Is that the problem?

There are off the shelf options like rechargeable batteries and keeping it plugged in while using the card reader, or batteries that hold more energy. That may be a simpler solution.

OTOH, all of this could just be a thinly veiled attempt to talk yourself into a nifty new calculator project. I've lost count the number of times I've done that. If that's the case then you absolutely have to do something about that horrid power supply. What were those engineers thinking! Sheesh!

-J

[TallKey]

(05-28-2023 10:03 PM)John Garza (3665) Wrote:  Maybe I missed something

SWAG: It could be right HERE or HERE

Or not...