Sharp PC-1211, battery question

[Dan C]

Can you use LR-44 batteries in a Sharp PC-1211 instead of the specified MR-44?
MR-44 seems to be 1.35V and not available today.
LR-44 is 1.5V, is it OK as a replacement?

[Jeff_Birt]

You can use a 675 hearing aid battery which are the same size and about 1.4~1.45 volts. That is what Radio Shack recommended for some/all of the PC-1 which are the same as the PC-1211. They are fairly cheap in quantity as well.

[Dan C]

(04-26-2022 06:02 PM)Jeff_Birt Wrote:  You can use a 675 hearing aid battery which are the same size and about 1.4~1.45 volts. That is what Radio Shack recommended for some/all of the PC-1 which are the same as the PC-1211. They are fairly cheap in quantity as well.

Thank you for the information on 675 battery!

[Dave Britten]

I use Energizer or Duracell 357s, which are basically a silver-oxide LR44, and they seem to work fine in both of my PC-1211s. You get outstanding battery life, and much lower risk of leaking than alkaline LR44s.

[Maximilian Hohmann]

Hallo,
the cheapest replacement type I have found are "AG-13" batteries. I paid less than 10 Euros for a pack of 100 on eBay, shipping included. They can be used for HP calculators of the Voyager series and many other calculators and small electronic devices too.
Regards
Max

[blackjetrock]

You can use LR44 batteries in the version of the PC1211 that takes 3 1.5V batteries. This seems to be a version that was sold by Sharp later on. They aren't very common but I do have one.
Alternatively you can maybe rewire the power circuit with a diode to drop the extra voltage. I did this on one of my PC1211s and it seems fine, although I am a bit dubious about the centre tap that the circuit uses. I need to revisit this mod and see if I can improve it.

I wrote it up here:
https://trochilidae.blogspot.com/2016/11...c1211.html

Andrew

[Dave Britten]

(04-27-2022 10:56 AM)blackjetrock Wrote:  You can use LR44 batteries in the version of the PC1211 that takes 3 1.5V batteries. This seems to be a version that was sold by Sharp later on. They aren't very common but I do have one.
Alternatively you can maybe rewire the power circuit with a diode to drop the extra voltage. I did this on one of my PC1211s and it seems fine, although I am a bit dubious about the centre tap that the circuit uses. I need to revisit this mod and see if I can improve it.

I wrote it up here:
https://trochilidae.blogspot.com/2016/11...c1211.html

Andrew

That's a good idea, I should probably do that to mine to make sure they're running a bit closer to the original spec. Did you have to cut any traces or remove any components to route through the diode?

EDIT: Okay, I see, seems simple enough. Interestingly, both of mine are different board revisions from yours. One has a diode and resistor already, and the other doesn't have any discrete diodes wired there. Should be the same principle though: just disconnect the red wire and reconnect it with a diode in series.

[Sukiari]

(04-26-2022 07:17 PM)Dave Britten Wrote:  I use Energizer or Duracell 357s, which are basically a silver-oxide LR44, and they seem to work fine in both of my PC-1211s. You get outstanding battery life, and much lower risk of leaking than alkaline LR44s.

This is the smartest option these days. That way one doesn't have to constantly take out and put in batteries if the device is forgotten for a little while because of yet another new toy!

[Dave Britten]

(04-27-2022 02:09 PM)Sukiari Wrote:  

(04-26-2022 07:17 PM)Dave Britten Wrote:  I use Energizer or Duracell 357s, which are basically a silver-oxide LR44, and they seem to work fine in both of my PC-1211s. You get outstanding battery life, and much lower risk of leaking than alkaline LR44s.

This is the smartest option these days. That way one doesn't have to constantly take out and put in batteries if the device is forgotten for a little while because of yet another new toy!

(Emphasis mine.) I feel personally attacked here. As I sit with a stack of Sharp pockets next to me.

I installed a diode in one of my 1211s as suggested by blackjetrock, and the screen contrast looks a lot better now. I always wondered why it seemed so dark... But strangely, my other 1211 seems to have rather high standby current. I noticed that the batteries in it were already down to ~1.25V, and putting a diode in that one dropped the voltage enough that the screen was very dim. Might just leave that one without for now...

[blackjetrock]

I wouldn't have noticed the contrast difference as I have swapped the display for a shiny new Robert Baruch one. It's really quite nice. the contrast is higher and it has a slightly different colour.

Andrew

[Nigel (UK)]

Having replaced the display in my Sharp PC-1211 last year, I used the 675 hearing aid batteries mentioned above to power it. On returning to the machine after a gap of several months I found that it wouldn't switch on; opening it revealed quite a lot of white powder inside the machine from the batteries. The 675 batteries are zinc-air and they have a hole in them to admit oxygen; the powder seemed to have come from this hole! I don't think that these batteries are intended to have a long useful lifetime once the sticker is peeled away to let the air in! (Fortunately the white powder brushed away without doing any damage.)

Next, I tried using four LR44 cells: the machine worked, but the unlit pixels always showed as grey.

So, instead, I'm using three LR44 cells to power this four-cell machine. I've shorted out the fourth cell compartment (the one at the top) and everything seems to work perfectly. Of course, the total voltage is lower than it should be, and a low battery warning will be triggered once the cells have run down a little. But if I use three silver oxide cells (3 x 1.55V), which keep an almost constant voltage until they are nearly exhausted, everything should be fine.

Has anyone else tried this? Is it a bad / good idea?

Nigel (UK)

[Gianfilippo980]

(04-30-2023 03:49 PM)Nigel (UK) Wrote:  Having replaced the display in my Sharp PC-1211 last year, I used the 675 hearing aid batteries mentioned above to power it. On returning to the machine after a gap of several months I found that it wouldn't switch on; opening it revealed quite a lot of white powder inside the machine from the batteries. The 675 batteries are zinc-air and they have a hole in them to admit oxygen; the powder seemed to have come from this hole! I don't think that these batteries are intended to have a long useful lifetime once the sticker is peeled away to let the air in! (Fortunately the white powder brushed away without doing any damage.)

Next, I tried using four LR44 cells: the machine worked, but the unlit pixels always showed as grey.

So, instead, I'm using three LR44 cells to power this four-cell machine. I've shorted out the fourth cell compartment (the one at the top) and everything seems to work perfectly. Of course, the total voltage is lower than it should be, and a low battery warning will be triggered once the cells have run down a little. But if I use three silver oxide cells (3 x 1.55V), which keep an almost constant voltage until they are nearly exhausted, everything should be fine.

Has anyone else tried this? Is it a bad / good idea?

Nigel (UK)

Today I switched to the same layout (3x1,55 V Silver oxide batteries), for the same reasons as above I didn't want to use Zinc-air batteries.
As an interesting sidenote, when I used 4 SR44, besides the grey screen, I had a problem where the FOR ... NEXT statement wouldn't work properly: it would execute the instructions in the loop just once, while most other commands appeared to work as usual. I feel like sharing this strange symptom, that surprised me, could help someone else who doesn't understand why their computer isn't looping as it should.
So, do you have any feedback about using 3 silver-oxide batteries on a 4 batteries model?

[laug]

I am using LR44 and one diode 1n4148, works great

[isidroco]

From first comment here: https://www.tindie.com/products/halfbake...p-pc-1211/

"I'm using THREE silver oxide batteries to keep the voltage close to the original four mercury batteries. The fourth (left-most) battery apartment I've shorted by a flipped battery."

So there's no need to solder or change original circuit, just use an old (or new) battery upside down which will jumper that compartment.