HP48GX RAM card design

[Marco Polo]

(01-21-2021 09:33 AM)wan Wrote:  There‘re two gold colored capacitors on the bottom right of the board, these two 440uf capacitors will provide power when changing batteries. They are larger than Paul's original design and provide longer holding time. I think they can hold for more than 20 seconds.

The reason for not placing the batteryholder on top is to avoid touching the batteryholder when pulling the card out. Pulling the card with batteryholder will apply shear force on it, which may cause the batteryholder to desolder over time.

Clever design, indeed.
Are you sure that 20 seconds are enough?
Just as an example, pulling-out the batteries from my Cynox cards requires some effort and doing it within 20 seconds is quite challenging

[wan]

(01-21-2021 04:12 PM)Marco Polo Wrote:  Are you sure that 20 seconds are enough?
Just as an example, pulling-out the batteries from my Cynox cards requires some effort and doing it within 20 seconds is quite challenging

The Cynox card covers the back half of the battery, so you can only pinch the front half of the battery to remove it. This makes it difficult to remove the battery.

My battery holder is bar shaped and the back half of the battery is exposed, so it can be easily pushed out. With a fresh battery ready to go, it takes less than 10 seconds to swap the batteries.

[Jonathan Busby]

(01-21-2021 04:12 PM)Marco Polo Wrote:  

(01-21-2021 09:33 AM)wan Wrote:  There‘re two gold colored capacitors on the bottom right of the board, these two 440uf capacitors will provide power when changing batteries. They are larger than Paul's original design and provide longer holding time. I think they can hold for more than 20 seconds.

The reason for not placing the batteryholder on top is to avoid touching the batteryholder when pulling the card out. Pulling the card with batteryholder will apply shear force on it, which may cause the batteryholder to desolder over time.

Clever design, indeed.
Are you sure that 20 seconds are enough?
Just as an example, pulling-out the batteries from my Cynox cards requires some effort and doing it within 20 seconds is quite challenging

I've found that using plastic tweezers is the best solution, for me at least. Just make sure that the gripping ends of the tweezers have a texture that makes it easier to grab onto smooth surfaces.

Regards,

Jonathan

[arborist]

(01-20-2021 10:25 PM)Jonathan Busby Wrote:  Well, I have the Seiko-Epson official catalog of SRAM cards ( and other memory cards ) with all the technical specs, but, unfortunately, I've moved to Colorado from Texas and most of my possessions are in storage ATM. I scanned the catalog and I have it saved on an external HDD but it is in storage as well. I also wrote down, a long time ago, all the salient information regarding HP48GX compatible memory cards, but, it again is in storage :/

Thanks Paul and Wan for your work on this. Wan, would you consider sharing the KiCad (or at least Gerber) of your middle board?

This is the most exciting HP48 project in a while!

Jonathan, did you get access to your stuff? I would love to have this information.

[okto]

(01-20-2021 10:25 PM)Jonathan Busby Wrote:  Well, I have the Seiko-Epson official catalog of SRAM cards ( and other memory cards ) with all the technical specs

Any update on making the PDF scans available?

@pdo, thanks for sharing this design. Would you consider GPL licensing this design, so it could be uploaded to GitHub? I think it would make it easier for future Googlers to find it, as well as open it up to a broader audience of folks who can debug and further develop the design in the future.