Energy meter using VFC

Discussion in 'General Electronics Chat' started by syee10, Feb 24, 2011.

  1. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Hi,

    I am designing an energy meter. Assume that i have an input to the VFC LM331 and i get an output from the VFC which is a clock pulse. How am i going to connect this clock pulse to a decade counter and display it on 7 segment display to obtain the 'energy' unit? I prefer using any IC chips than PIC. Anyone please provide me any useful information.

    Note that averaging the power(this is the output of VDC) over a period of time we get the energy.
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    Which microcontroller do you want to use?
     
  3. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Bill,

    I prefer do it without microncontroller.. just using IC chip.. can you help me?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    If your device varies output freq. with changes in input...?

    You would send it to a freq to voltage converter circuit and then use an analog to digital conversion. Your display circuit would need to 'sample' the output of the A to D converter and provide the sample data to the display driver chip. The sample rate will determine how fast the display can change values. Fast rates are good but can be difficult to see clearly if the input is changing rapidly.
     
  5. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Kermit2,

    Can you tell me more about 'sample the output of the A to D converter' ? Thanks
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    What exactly do you want to measure? If you want to measure and display power, you need to know the voltage and current consumed, then multiply. In most systems voltage is constant and current varies, so you need to measure only current.
    The best solution I see is integrating the current and periodically sample and reset the "counter" - the integrated value. Then feed the sampled value to a 7136.
    I will try to sketch a schematic.
     
  7. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    kubeek,

    The input of my VFC is actually the output of an analog multiply. The output of analog multiplier is actually the multiplication of current and voltage signal. It other words the output of multiplier is the power component. This power component is then fed into my VFC. The output of VFC is a pulse signal in digital form which is directly proportional to my input to VFC. Am i right until here?
    What i need is energy for my final result. So what i need to do is fed the output of VFC into a decade counter and latch and show it on 7 segment display. The digit shown in 7 segment display represents my final result (energy).
    So my problem here is i dun know how to connect the circuit from my output of VFC to decade counter (e.g 74ls90) and latch (e.g 74hc4551) and 7 segment display.
    Am i make my problem clear now? Please provide me assistance =)
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Since you are only going to display 0 - 9, you can simplify the problem by using the analog output and applying it to an LM3914 - http://www.national.com/mpf/LM/LM3914.html

    The complication in your current methodology is that you have to find the range of frequencies that span your range of interest, and be able to display some meaningful number (one that shows watts might be desirable). That might require more counters and some timing source to define counting periods. In essence, you are making a frequency counter that indicates power rather than frequency.
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    If you are getting a DC level which varies with the power level

    \\\

    Why convert it to a freq?

    A panel meter can take a varying low level DC voltage and with some scaling adjustments(setting high and low points) display almost any range of numbers you require.

    Set a scale for 0-100, or 0-10 and set high and low points on the input to correspond to the input voltage level.

    Presto - your small DC varying voltage will display as a 'true' value in watts
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Duh - meter is better.
     
Loading...