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A repository for managing (public) resources and issues underpinning the ShrimpingIt website
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Clock Kit #25

Open cefn opened 10 years ago

cefn commented 10 years ago

Would be good to prototype and ship a simple kit based around an RTC. Could feature people's experiments with alternative clock builds... http://playground.arduino.cc/Main/RTC-PCF8563#Example

Need some kind of default clock behaviour out of the box, though, and it's not easy to know what this could be at very low cost - e.g. displays and servos tend to be a little expensive.

Could possibly make up a clock indicator with 24 LEDs, but there may be a better default presentation which is distinct from the POV

cefn commented 10 years ago

One technique for this could be to line up three shift registers to serve a total of 24 lights on a 400pt breadboard, which could be used for hour and minute display directly, or could use a layout superimposed with a craft construction to make a word clock... https://www.google.co.uk/search?q=word+clock&tbm=isch ...which only needs 22 of the lights.

Serial should be used for periodic reporting of time from the RTC, as well as for setting the RTC

cefn commented 10 years ago

This has now been prototyped with a pair of WS2803 DIP chips, with blue and green leds. The RTC is not yet in play as we are missing a crystal, but instead the code emulates a clock to the precision of the Arduino's own timing circuit, set via Serial.

cefn commented 10 years ago

There's potential to complete this with a 32.768 Crystal driving timer2, although this use could invalidate PWM on Pin 3 or Pin 11 and perhaps other collisions with use of timer2. However, it could eliminate the need for an external RTC chip. One advantage of the Dallas 1307 is to manage an external backup power supply to keep the clock alive, though, so it is slightly preferred. If the ATMEGA is geared up to detect changes to power supply (turn off LEDs) then could possibly achieve this with just a couple of diodes threaded into the circuit between watch battery and ATMEGA, and between WS2803 and ATMEGA, preventing the watch battery from being used or being charged up when power is attached, and also preventing the LEDs from being powered up when running only on watch battery. A finer isolation model could also pull the WS2803s latent draw out of the circuit.