A thermostat calendar circuit

Discussion in 'Embedded Systems and Microcontrollers' started by Stevengeerts, Oct 5, 2011.

  1. Stevengeerts

    Thread Starter New Member

    Oct 5, 2011
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    Imagine a roomthermostat containing a clock and a calendar. All that does is opening/closing a circuitbreaker. It therefore stores a point in time on the internal calendar when the measuring resistor should compare with the related temperature for that point in time. Usually these thing can store 3 week and 1 weekend program.

    Say now I want to build a circuit that only has the clock/calendar functionality with the possibility of opening/closing a circuitbreaker (no input values like temperature need to be read). Because I would like to schedule my points in time on a custom base, with a granularity of 1 minute and this for 50 years, I would need 100Mbyte of storage when the dates+times are stored in BCD and say if I would alternate each minute (this is the maximum of possibilities).

    What Pic - Memory combination would I need for that kind of circuit say if I would like to store the dates by means of my PC using a USB interface ?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    First, you don't need 100MB space to store the data because hopefully no one sane will set a switch event for each minute, but lets say 500 per month seems reasonable.

    As for the micro-memory combination, I had a good success with atmel's atmega interfacing an SD card. I used atmega 128 with 4kbyte of RAM and it was plenty, with an FTDI uart-to-usb converter, but there should be better ones with embedded usb interfaces.
     
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  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Using Microchip's application libraries it is fairly trivial to add both USB and SD card capabilities to an application.

    I've done just that several times with several devices.
     
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