HP-48 FRAM Cards

[matthiaspaul]

(08-19-2016 12:06 AM)JDW Wrote:  

(08-18-2016 09:56 AM)matthiaspaul Wrote:  I find the design and finish of that seller's cards somewhat distracting. There's so much that could be done better that I'm considering making my own design... (If I only had the time... ;-)

Maybe I should hold out for your edition then? :-)

Seriously, from day one I was concerned about that FRAM card design (even the SRAM cards from that same seller) simply due to "static discharge." As you know, all the old HP and third party cards were made very well in that they were completely covered. Not only did that protect the expensive circuitry from death-by-static, but it also covered the PCB so your eyes are never distracted!

So if anyone would kindly sell us FRAM cards at half the price of that EBAY seller, I think we could sell quite a few, with myself being first in line!

If I'd do it, these would be my design goals:

Mechanical design:

- thicker composite board 3D design to more closely resemble the original card dimensions. This will improve the stiffness of the card (to reduce the risk of damage by bending), it will eliminate "wobble" in the slot (for a better electrical contact, reduced wear of the connector contacts and longer life in industrial and/or vibrating environments), it will give a better and more secure grip when removed, and it will protect the "recess"-mounted chips from all too easy mechanical damage and being easily touched (ESD).
- possibility to fill the central recessed area of the card (where the chips are mounted) with epoxy to actually seal the chips - would reduce the ESD vulnerable area almost down to the card's contact area, but would make any repair impossible
- some kind of eject grip
- rounded corners
- (I spoke to a mechanical engineer about the possibility to design a spring-loaded flap to protect the contact area, but I doubt it will be possible to find an affordable solution for small batches)

Electrical design:

- 2 MB (if still possible to place with all the extras: 4 MB)
- high-quality FRAM chips (there are considerable price differences between chips up to factor 3: some of the cheapest chips I saw have read/write endurances of only 10^10 cycles, specified data retention times of about 10 years (at +85°C, though, but no specification for lower temperatures), and draw currents of up to 20mA active and 20µA in sleep, whereas some of the most expensive ones have 10^14 cycles, specified retention times of several decades (at less than +85°C, that is), and draw less than 12mA active and 8µA in sleep)
- better ESD protection (although perhaps not perfect)
- global hardware write protection switch
- reconfigurability to bankswitched memory for HP48SX compatibility (and to support 4 MB on 48GX without bogus error messages)
- micro-USB interface for easier and faster data transfer and card backup to PCs, possibly also as alternative power supply to save batteries (I would have to check HP48 schematics to see if this would be possible without modification) [EDIT: Unfortunately, an external power supply facility is technically impossible without a minor hardware modification in the calculator. A quirky and only partial solution would be a short external cable from the card to the serial port, but I don't think this would be very practical.]
- possibly integrated micro-SD card slot for local backups (peak power-consumption could be an issue - to be checked)
- possibly integrated wireless connectivity (BT? NFC?) (peak power-consumption could be an issue - to be checked)
- special power design to minimize power consumption
- quality placement and layout artwork adhering to established electrical design rules, not the result of some kind of wierd auto-placer and -router

Firmware design:

- Microcontroller emulating an USB mass storage device with virtual FAT file system to access the various HP ports
- Software configurable write protection of indivitual ports
- SD card could work as a "shadow" background storage medium to store "snapshots" of ports when set to read-only
- Possibility for a direct data channel to transfer individual values between a HP48 and a PC or smartphone application

Software:

- HP48 application software or library to enable/disable write protection and switch banks
- HP48 application software or library for directly transfer data

Finish:

- DIY parts kit? Self-assembled? Professionally made? Firmware / software a community project?

Greetings,

Matthias