hall effect signal on to 7seg display

Discussion in 'The Projects Forum' started by ralphh85, Aug 29, 2007.

  1. ralphh85

    Thread Starter New Member

    Aug 29, 2007
    hello im new here! hopefully someone on here can help me!

    basically im tryign to bring up a number on a few 7 segment led displays dependent on the amount of pulses per min which come from a hall effect sensor.

    i believe i will have to convert the hall effect signal to an analog dc voltage then put this in tot he LED display.

    but where do i start? i have little electronics knowledge and dont have time to go back an do my A level!!

    any ideas?

  2. beenthere

    Retired Moderator

    Apr 20, 2004
    You can get Hall effect sensors that have a digital output level. Apply the pulses to a counter chain, with a display showing the accumulated number.
  3. mrmeval

    AAC Fanatic!

    Jun 30, 2006
    A digital output can be done with a "hall effect switch"

    If you are not constrained as to how you count them or output them look at something like a pic, atmega, picaxe or other microcontroller solution.

    I like this http://www.arduino.cc but there will be an investment in learning it and then having it read the sensor and then output to a display of some sort.
  4. ralphh85

    Thread Starter New Member

    Aug 29, 2007
    well what im actually doing is...

    i have an old metro which has real fast engine (143bhp vvc engine) and also a carPC. windows based small mini itx pc used for playing music mostly.

    i want to remove my instrument cluster (speedo/rev counter/water temp/ etc etc) and replace it with a set of digi dials which i would really like to make myself as would be a good project!

    the speedo sensor which i can put in (from a rover 200 or similar) is just a hall effect sensor and it gives out 4 pulses per revolution.

    so i have the output i just need to bring it in and show up XXXmph.

    i am totally open to ways of doing it with no restrictions, most of what was said/the pages i just viewed kinda went over my head!

    whats the easiest way? i can wright basic software so must be able to pick it up somehow!

    cheers for help
  5. ralphh85

    Thread Starter New Member

    Aug 29, 2007
    i now know that obviously 0hz = 0mph

    and not so obviously 120hz = 129mph!! on my car this may be closer to 120hz = 122mph due to different gearbox tho but i would like it to have adjustament anyway!

  6. kender

    Senior Member

    Jan 17, 2007
    You could use a panel meter. It’s an OEM device that takes an analog voltage and displays it on 7LED or LCD (depending on a model, of which there are hundreds).

    Now, you need to convert pulses per minute to analog voltage. There are 2 possibilities:

    - If the pulses have constant width, then the duty cycle is proportional to the frequency. Then you can simply low-pass filter pulsed signal to convert it to DC voltage level.
    - If the pulses have a constant duty cycle, you could use a frequency to voltage converter (F/V). You can make one out of a 555 timer. Or you can get an F/V IC such as LM2917.

    Of course, you can do all this with a microcontroller too.