USB powered HP41

[Neve]

Hi all,

I'm kinda new here. So excuse me if I ask questions that where asked of discussed many times around.
After some research, I camo across several posts On this subject. Like this one for example:

http://www.hpmuseum.org/cgi-sys/cgiwrap/...722#183722

I thought of using an iPhone wall USB plug as the power supply. It delivers 5V/1A

Several issues come to mind, though:
1- Would the 5V provided by the USB suffice to properly power the card reader?
2- Shouldn't the battery pack be removed before plugging in the USB power supply? If not, it will probably add another 5V or 6V depending on the current battery charge! (I haven't seen the schematics yet). Could the circuit handle it?
3- Does anyone know where the + and Grnd are on a Fullnut circuit board if I decided not to use a module/slot? That would save me some time if I decide to go that route.

I have an idea that I will gladly share if I can make this work.

Thank you all.

[Jlouis]

Hi,

For now, I just want to answer your #1 question:

Although I don't know the nominal eletrical current necessary to supply the HP 41 and the card reader, I don't think that a source of only 0.15A would be enough to do the task alone.

The problem here isn't a question of increase Voltage. The source must have the necessary power to do the job, i.e., nominal voltage multiplied by the current in Amperes.

The current is actually a function of the voltage divided by the resistance (load).

If you know the demand current for using the card reader, you will be able to design your source.

Now, HOW you are suposed to CONNECT the power source to the main board of the calculator, is another issue.

Good luck,

Cheers

JL

[Sylvain Cote]

(09-07-2017 09:40 PM)Neve Wrote:  I thought of using an iPhone wall USB plug as the power supply. It delivers 5V/0.15A

You must be using a very old Apple AC-to-USB plug.
For several years now, Apple has made available a very small plug who can deliver 5W (5V@1A) who should be enough for your need.

https://www.apple.com/shop/product/MD810...er-adapter

Sylvain

[Neve]

(09-08-2017 12:55 AM)Sylvain Cote Wrote:  

(09-07-2017 09:40 PM)Neve Wrote:  I thought of using an iPhone wall USB plug as the power supply. It delivers 5V/0.15A

You must be using a very old Apple AC-to-USB plug.
For several years now, Apple has made available a very small plug who can deliver 5W (5V@1A) who should be enough for your need.

https://www.apple.com/shop/product/MD810...er-adapter

Sylvain

Very old AC-to-USB plug? Nope, it's the one that came with my iPhone 7....
But I misread, very small print. It is indeed 1A. I'll edit the OP. Thanks.

[Neve]

(09-07-2017 11:55 PM)Jlouis Wrote:  Hi,

For now, I just want to answer your #1 question:

Although I don't know the nominal eletrical current necessary to supply the HP 41 and the card reader, I don't think that a source of only 0.15A would be enough to do the task alone.

The problem here isn't a question of increase Voltage. The source must have the necessary power to do the job, i.e., nominal voltage multiplied by the current in Amperes.

The current is actually a function of the voltage divided by the resistance (load).

If you know the demand current for using the card reader, you will be able to design your source.

Now, HOW you are suposed to CONNECT the power source to the main board of the calculator, is another issue.

Good luck,

Cheers

JL

Problem solved, it is 1A, not 0.15A, as Sylvain Cote pointed out.
Error corrected in my original post.

Thank you.

[Neve]

Someone pointed out to me that another issue would be that the USB should NOT be charging or try to charge the alcaline batteries.
So I guess they'd have to be removed. Which answers the question regarding the possible increased voltage.
That leaves another question: is 5V/1A enough to power both the calc and a card reader appropriately?

I wouldn't want to damage an otherwise very clean tall-keys HP41C (which, BTW, will be receiving a CL board as soon as one is available)

Thanks

[Jlouis]

No, alcaline mustn't be charged. Only NmH or NiCad batteries.

Unless someone has any point against it that I'm not aware, you can remove bateries and plug your source.

5 volts is ok, but again, even though 1A looks good, I have a HP 97 that have the same card reader of the 41 plus a printer, and that beast drains 3 amps in full charge (peak), but I don't recall if reading a card or printing, so be aware that your apple usb charge should not be enough, but I will let someone more knowledgeable in the 41 confirm its maximum current amp drain.

I read Diego post sayng a USB port can be used, but bear in mind that he should have referred to a PC USB port, which is supplied from an at least 500w power supply, very different from a iPhone charger.

If I can suggest you, I recently bought a power supply for my 97, 5 volts, 5 amps, regulated ( it maintains 5 v no matter how the load fluctuates), for less than the equivalent of 10 US$, so I think it is a little investment that you can make to have piece of mind.

Here is a link for a 5v, 2A power supply in Amazon, but you can certainly find a 5A in ebay or so on.

Good luck.

Cheers

JL

[Neve]

Jean-Louis,

I sent you a private message