work in progress



Looks interesting, looks like a "big enter key" keyboard - but what is it??


Yeah, Eric. That's like telling half a joke... Come on...


Obviously I'd like it to be some sort of calculator, but it isn't there yet. Right now it's just prototype hardware that doesn't do much more than scan the keyboard, display test messages on the LCD, and test energy consumption in various modes (running at various frequencies, sleeping at various frequencies with and without peripherals enabled, etc.

The processor is an Energy Micro "Gecko" microcontroller, which uses an ARM Cortex-M3 core. This has very low power consumption in both active and sleep modes. There are a few other microcontrollers that get lower uW/MHz, but they generally don't have nearly as much compute performance per clock cycle, so the Gecko might actually have the best power/performance ratio.

I wired this up to verify their power claims, and to determine whether a calculator using it could have a decent battery life on a pair of lithium coin cells. Now that I've answered those questions, I'll move on to the fun part.


Hello Eric,

Can you post your power consumption in Off mode, Idle mode (LCD on) and in running mode (indicating the frequency?)

thanks, cyrille


Hi Cyrille!

This is the EFM32G290F128, which has 128KB of flash and 16KB of RAM. All 16KB of RAM is preserved in sleep mode, though it is possible to turn portions of it off to save even more power. I haven't done that.

Off mode (32 kHz osc running, wakeup on timer or key press): 1.6 uA

The LCD I am using is just some random surplus character LCD module, so it doesn't make any sense for me to report power consumption with that. Without the LCD, idle mode is nearly the same as off mode, since the CPU isn't doing anything different other than scanning the whole keyboard rather than just the ON key. There is a version of this CPU with on-chip LCD controller for up to 160 segments, but I'm not using it, so I haven't measured its power consumption.

Running mode, internal RC oscillator, zero wait state flash:

1 MHz:  450 uA
7 MHz: 2.4 mA
11 MHz: 3.4 mA
14 MHz: 4.1 mA

Running mode, internal RC oscillator, one wait state flash:

21 MHz:  4.6 mA
28 MHz: 6.1 mA

Running mode, external crystal, one wait state flash:

32 MHz:  7.2 mA

What currents have you measured for your AT91SAM7L128-based calculators?


Edited: 18 Mar 2010, 7:09 p.m.


If you really want a half-joke: "Why does the porridge-bird lay his eggs in the air?"

Or: "What's the difference between a Vulcan and a revolving door?"


Awesome... a Firesign Theatre reference!! "I see you are a sailor..."


I recognize the layout ;-)

Cheers, Geoff


Interesting. Looks like a 41 keyboard with a dual line display a la 42? Could this be a 41/42 hybrid?

I am not an electronics guy, so this is just a guess...


Looks very interesting. Seems to become something like a 48, taking the number of keys into account. Are you sure you're striving for a pocketable device? d;-)

Ceterum censeo: Launch a 43S.


I'm not likely to do anything like the 28, 38/39/40, or 48/49/50 families; implementing the software for those would take too long. (Though if someone else wants to write the software...) Like the earlier DIYRPN calculators Richard Ottosen and I have made, this prototype has enough keys to compare with the various pre-Saturn handheld calculators.


Could be a platform for Free42. Does the design care for I/O?


The only likely I/O is a serial port, and an SD or microSD card slot.

There's only 128KB of flash, not enough to fit Free42. I also didn't put enough keys for Free42, though that could be fixed easily. It's also really hard to find a suitable graphic LCD module for Free42, that isn't physically too wide for a handheld calculator.


OpenRPN had a fairly complete RPL implementation which could be used.
Otherwise, my 20b firmware would easily fit.

- Pauli


Otherwise, my 20b firmware would easily fit.

As an extra benefit, a "real" 2-line dot matrix LCD combined with that would open new opportunities compared to the 20b/30b.

All of the code written for OpenRPN is still up on the sourceforge svn. I also still have all the documentation and I would love to help out with a project like this or any of the current repurposing concepts.

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