Microcontroller for a timer circuit

Discussion in 'Embedded Systems and Microcontrollers' started by CognacHimself, Aug 5, 2014.

  1. CognacHimself

    Thread Starter New Member

    Aug 4, 2014

    I am working on designing a 24 hour countdown timer and have decided to use a microcontroller to execute. I will likely be using a MEMS-based IC oscillator to replace a traditional crystal oscillator that will feed the microcontroller a fixed frequency for period pulses. I plan to implement 4 push button switches to control the increment of time, decrement of time, a start function, and on/off switch. The output will likely just be an LED that will blink upon countdown completion with a second output for possibly triggering another device such as a FET.

    Is there any microcontrollers that you may recommend for an application such as this? Likewise for power supply. I'm not sure what sort of approach Id like to take for selecting a proper and adequate power supply (the smaller the better).

    Any input would be great! Thanks!
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    I think just about any uC can do it.

    What is your budget?
  3. takao21203

    AAC Fanatic!

    Apr 28, 2012
    You can use these for power supply. Outside US you need adapter plug but they also work from 230 volts.

    What about a PIC 16F1709 + Nokia5110?

    Or a micro Arduino board.
  4. MMcLaren

    Well-Known Member

    Feb 14, 2010
    Just about anything should work. I posted a single chip four digit 99-minute timer here which may give you some ideas. It uses the internal oscillator but could easily be changed to use a 32768 Hz crystal for the time base.

    Good luck on your project.

    Cheerful regards, Mike

  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    As described you have 1 clock, 4 inputs, 2 outputs (1 for future expansion), plus power and ground pins means you need most any device with 9 or more pins.

    But with four buttons to set the time... what time? How will you know what time you have set?

    Somewhere down in the Completed Projects sub forum I have a timer that is programmable, with start and stop features, along with auto power on and off (when not timing it is off) that just needs one button, but there is a speaker that beeps out what it is doing. It uses the relatively inaccurate internal oscillator as that met the design spec of “about” 1 to 10 minutes.
  6. CognacHimself

    Thread Starter New Member

    Aug 4, 2014
    No real budget restrictions currently as it is just in the initial design phase.

    Good point on knowing what time is set, cant believe I didn't realize that. So yes, some sort of user interface will be necessary. But, I would like to stay away from 7 segment displays so I can keep overall size to a minimum.

    This will eventually be laid out using PADS and fabricated. Thanks for the input everyone!
  7. CognacHimself

    Thread Starter New Member

    Aug 4, 2014
    I'm thinking if I end up using a microcontroller with an internal oscillator simply using a 20mm coin cell battery with an SMT adapter would work just fine for a power supply as well.