how much miliamps uses my circuit???

Discussion in 'Homework Help' started by eric_s88, Jan 21, 2012.

  1. eric_s88

    Thread Starter Member

    Apr 20, 2011
    Hi every one
    Its an alarm clock circuit which shows time, and the alarm time in a 2*16 character LCD, and have 4 push buttons for adjusting time and alarm time, I have used an atmega16 as micro.

    I wish to know with full LCD back light on, how much miliamps uses this circuit, and may I run this with a usual 9V battery for a long time???

  2. Georacer


    Nov 25, 2009
    Your main consumers are the atmega, the buzzer and the LCD. Do you have datasheets for these components? They mention current consumption.

    A 9V battery has approximately 900mAh, if I remember correctly (maybe even less). After you find the current consumption of your circuit, you can calculate its possible uptime.
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    The LCD datasheet I found doesn't mention the backlight, is it possible that this is another part number? Do you have a complete datasheet?

    Why does the backlight has to be on all the time?

    The current for the Atmega depends on the frequency it is running at.

    See the datasheet for details. Page 292. It ranges from about 1mA to about 15mA when it's active.

    Since you said "long time" I guess you don't need to consider the buzzer and the reset pull-up resistor. The potentiometer of course will cause 500uA at 5V.

    The circuit is not complete as the power supply is missing. Is there any other resistors connected somewhere?
  4. eric_s88

    Thread Starter Member

    Apr 20, 2011

    yes you are right, but the buzzer is now always on, I think the most consumer is the LCD backlight..
    anyway.. if we have the current consumption of this circuit how should we calculate its uptime?? ( with a 900mAh)

    thank you
  5. eric_s88

    Thread Starter Member

    Apr 20, 2011
    HI, no I have the same datasheet that you mentioned and there is written that optical data is on page 7 , but its only 2 page!

    I think the lcd backlight most be always on because I want to use it as a clock, and without the backlight it will be impossible to see the time..

    I use a 4MHz external crystal for atmega frequency..

    this circuit is a simulation and the power supply is not shown, but it is connected, a 5volt for atmega and a 5volt for lcd backlight...

    thank you
  6. Audioguru


    Dec 20, 2007
    The backlight might have 8 LEDs operating dimmly at 6mA each and the clock might use 2mA for a total of 50mA.

    The datasheet for their 9V alkaline battery on Energizer's website shows that it can supply 50mA for 10 hours (500mAh) when its voltage drops to 6V.
    Will the clock still run? Will the LEDs still be bright enough?
  7. eric_s88

    Thread Starter Member

    Apr 20, 2011

    oooops! so it seems its not a good idea to use a 9V battery for this circuit...

    what should I do??? I can run It with a power supply but then it wont be portable..

    any idea???

    thank you..
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    4 AA batteries would give you 2500 mAH.

    The drain of the uC and LCD are pretty minimal compared to the LCD backlight.

    Figure out a way to not use backlight until a button is pressed and the batteries will last a long time.
  9. eric_s88

    Thread Starter Member

    Apr 20, 2011

    it sounds good! so I should make a little change in my C code in order to keep the backlight off until a key is pressed,

    thank you thatoneguy;)

    if other guys have another idea , please share :)