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
    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


    Sep 20, 2005
    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.
    Stevengeerts likes this.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    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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