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µWatch unofficial FAQs

The uWatch is an RPN and Algebraic scientific calculator watch that you can build yourself. The software is open source under the GPL license at Sourceforge. I'm assuming you've already read the official uWatch FAQ, so we'll jump right into some more technical details.


The history of the uWatch mentions the 53mm x 20mm compact 16x2 line LCD that convinced David L. Jones that the uWatch project was actually doable with off-the-shelf components. If you are doing low-level programming of the uWatch, such as making "custom characters", you might want to look at the datasheet (via "Moon Phases").

Alas, that original display pulls about 2 mA, more power than anything else on the uWatch -- even the CPU uses less power (at 250 KHz). That's the main reason the current uWatch cannot run the display continuously (like a standard watch), but much be explicitly "turned on" every time you want to read the time.

The current uWatch2 rough draft seems likely to use the Newhaven NHD-C12832A1Z-FSW-FBW-3V3 128x32 Pixels display. Which uses less than 100uA which would enable a continuous display watch. The "white LED backlight" uses 30 mA at 3.0 V but is still very usable at much lower currents.

Proposed displays:

  • Newhaven NHD-C12832A1Z-FSW-FBW-3V3: 128x32 pixel display, white LED backlight, 41.4mm x 24.3mm (current top runner)
  • Newhaven NHD-12864WX-T1TFH# Graphic LCD: 128x64 pixel display, white LED backlight, 38.0mm x 26.4mm
  • CFAX12864AP1 Graphic LCD: discontinued, apparently replaced by CFAX12864T1.
  • CFAX12864T1-WFH Graphic LCD: 128x64 display with EL backlight. (the EL backlight version seems to require less power than the white LED backlight version).
  • card display: 6 digit, 7 segment display module designed to fit inside a credit card. lightest-weight display of those on this list; adequate for 4-function calculator watch. Doesn't seem to show enough information for a scientific calculator.
  • Sparkfun LCD displays: the color graphics LCD cell phone displays look relatively low power and are extremely well documented -- some of them are under $20.
  • ...
  • ... Have you seen a display that would work on a wrist calculator? Please add it to the list here! ...

Some threads discussing diplays: "Hardware Stuff » Why not a smaller LCD...",


The buttons are crucial for a calculator watch. It is difficult to compromise between:

  • fast typing speed:
    • it's much faster to have lots of buttons, so you can directly push a button for "tan" than to scroll through some soft menu searching for it.
    • large buttons are generally faster to rapidly punch than tiny, closely-packed buttons
  • physical size:
    • We want something that is not too heavy and bulky to wear on the wrist. This means lots of large buttons are not going to happen.

The first uWatch prototype used surface-mount buttons. The original uWatch for sale uses the (through hole!) Panasonic EVQ-PJG05Q switch for its buttons. [1] (current price)

  • please tell us about other buttons that would be appropriate
  • ... capacitive touch "buttons" ? ...
  • ...


The processor is, perhaps surprisingly, not a crucial choice. In the last few years, several companies have released processors that meet the stringent low-power and other requirements (which are????). In theory, since most of the software is written in the C programming language, it is theoretically easy to port the software to a different CPU.

The original uWatch uses the 16 bit Microchip PIC24FJ64GA004. It uses 50uA at 32KHz, ... (FIXME)... uA at 250 KHz.

Other proposed processors have been discussed on this thread: "Hardware Stuff » Ideas for Mk2 watch".

... the Microchip "Extreme Low Power Microcontrollers" claim to have "Real-time Clock/Calendar down to 500 nA". http://www.microchip.com/xlp

Nate gives some low-power tips in "Adventures in Low Power Land".

Arne Martin Holberg and Asmund Saetre. "Innovative Techniques for Extremely Low Power Consumption with 8-bit Microcontrollers".

further reading

Late breaking news: there is now another µWatch wiki; is that the Official µWatch wiki? Feel free to move all the content on this page to that wiki. --DavidCary 15:58, 19 November 2009 (UTC)

Oops, that wiki has gone offline. So we'll keep this wiki page at Open Circuits. --DavidCary 23:08, 4 September 2011 (UTC)

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