HP-48 FRAM Cards

[matthiaspaul]

(08-25-2016 03:19 PM)gege Wrote:  I also thought about creating my FRam card because the one available on ebay is too expensive (for hobbies usage),

Of course, a 2 MB or 4 MB card would still be expensive (when compared with flash or SRAM), simple because FRAM is a comparibly expensive technology.
Prices could be reduced significantly by using older generation FRAM chips, but at the expense of significantly lower endurance (10^10 to 10^13 cycles rather than 10^14 to 10^15 cycles), a lower data retention time (although all chips still seem to allow 10 years) as well as a significantly higher power consumption. Since I see it as a one-time investment and this is a battery-powered device, I would tend to use the best chips available (within reasonable price limits), not the cheapest.
Things would be different, if we could use MRAM, as this is available in larger capacities and for much lower prices - however, all MRAM chip specs I studied so far also indicate a significantly larger power consumption in active mode than FRAM, and longer startup times, which would make it impossible to implement some power management schemes. So, they do not seem to be the ideal choice for battery-powered devices.

Quote:but currently I have no the time to do it

Same here.

Quote:I was thinking to add GPIO to connect external hardware to the HP.

I was thinking about that as well, but not in form of "raw" GPIOs on the card, but more by providing a connection to some external hardware and control GPIOs in that external hardware through some standard protocol. I2C would be a possibility, but TTL-serial might be a much better choice given that the HP48 already has a RS-232 interface, and I2C could be implemented only by indirect means. Having the GPIOs in an external hardware would also eliminate ESD and power supply issues.

(Sidenote: If I would design a 128 KB card for slot 1, I would try to include a port replicator for the LCD interface, so that it would be possible to use the overhead unit in parallel to a memory expansion card, or even better, reroute the outgoing LCD data through USB (or wirelessly) to display the LCD contents on a PC or smartphone display.)

Quote:And perhaps an esp8266 module to have wifi connection.

The main problem with WLAN is power consumption. The suggested module would consume 130 to 220 mA in typical use. That's way above of what I would want to draw from the HP48 - in fact, even though I don't know the exact figures yet, I doubt the HP48 can provide this much current without being damaged. In comparison, BLE is more like 10 to 15 mA - this is in the region of what I expect the HP48 is able to deliver on a card slot without problems. After all, the HP48 was designed to supply SRAM cards only.

(BTW. This may also rule out SD cards. Some SD cards can draw currents beyond 200 mA, although typically in faster modes only. I would find it unsuitable if the user had to select a special "low power" card for usage with the HP48 instead of using whatever is in reach. This wouldn't be a problem for as long as there is also a USB cable plugged in at the same time, but having a direct connection to a PC makes an SD card pretty much obsolete anyway. So, it seems, this combination of features does not make much sense.)

WLAN may also cause EMI problems.

Greetings,

Matthias