1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Lcd or led display tachometer. How can i build one?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by swiftakias, Mar 5, 2004.

  1. swiftakias

    swiftakias New Member

    Joined:
    Mar 5, 2004
    Messages:
    2
    Likes:
    0
    :!: I want to build a tachometer with a lcd or led display to watch my rpm of my car. Can anyone knows or knows a site that can i find something?. I need a schematic please..:roll:
     
  2. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    You can use Frequency to Voltage converter feed by your ignition coil, and the output connected to a Digital volt meter or LED BAR driver like LM3915.
    The best is to use some kind of FQ counter or MCU "PIC/AVR?" to get the number of pulse per second then dived with the number of cylinder of the engine, multiply the result with 60 and you get teh RPM.
    Example: the counter counted 100 pulse in one second, your 4 cylinder engine ignition coil make 4 sparks per 1 rotation, 100/4=25, 25*60=1500 RPM, and you done.
    :idea:

    Correct me if I'm wrong.. :!:

    Steve
     
  3. tomc_ar

    tomc_ar New Member

    Joined:
    Mar 5, 2004
    Messages:
    1
    Likes:
    0
    Last edited by a moderator: Dec 26, 2013
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. diode

    diode New Member

    Joined:
    Feb 22, 2004
    Messages:
    24
    Likes:
    0
    Location:
    Oulu - Finland

    Wouldn't that be 2 sparks per 1 rotation? I think cylinders work in couple.

    Besides the math, counting the pulses on ignition surely is a way to read RPMs.
     
  6. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    You are right about that.. :roll:
    Here is what I come up in about a 45 min.

    I did not have the chance to try in the real word /1am in the morning/, but it is working fine in the simulator.
    Painfully simple, maybe not the most accurate,I think should be able to get down to the 5 RPM.
    Look at the schematic and the code, I think it should be working fine.
    If my math is incorrect again, you can easily adjust that.
    Download Crownhill Picbasic Lite and compile with it.

    If you want to check it out yourself before build it, get the Proteus DEMO.
    Code (text):

    DEVICE 16F84
    DECLARE  XTAL 4
    DECLARE  LCD_TYPE 0
    DECLARE  LCD_DTPIN PORTB.4
    DECLARE      LCD_ENPIN PORTB.3
    DECLARE      LCD_RSPIN PORTB.2
    DECLARE  LCD_INTERFACE 4
    DECLARE      LCD_LINES 1
    PRINT $FE,128
    W0      VAR     WORD

    START:  
       COUNT porta.0,1000,W0     ' COUNT FOR 1 SEC
       W0=(W0*10)/2
       CLS
       PRINT DEC W0*6," RPM  "
       GOTO START    
    God luck
    STEVE
     

    Attached Files:

    • TAC.GIF
      TAC.GIF
      File size:
      6.3 KB
      Views:
      10,795
  7. Hivolt

    Hivolt New Member

    Joined:
    Mar 6, 2004
    Messages:
    15
    Likes:
    0
    Location:
    Canada
    In a four stoke engine the distributor rotates at half the crankshaft speed, therefore the coil fires half the number of cylinders per revolution. On a 4 cylinder engine the coil fires twice per revolution. A tachometer is really just a frequency counter with a different timebase - some basic math to check your results would be engine rpm X (1/2 # of cylinders) /60 = pulses/ sec ( Hz ). i.e. for a 4 cyl engine. 1500 Rpm x2 /60 = 50 Hz
    2000 Rpm x2/60 = 66.66 Hz
    3500 Rpm x2/60 = 116.66 Hz
    and so on.

    To turn these frequencies into tach numbers you will need to gate the count by 3.33 Hz i.e. 50 Hz / 3.33 = 15 ( 15.0150 ) So on a 2 digit display you would see 15 then add 2 digits reading zero's behind for appearance sake. By using a slower gate time you could get more resolution but the display would be painfully slow updating. You could of course multiply the input frequency by 10 times which would give you an extra digit of resolution with the 3.33 Hz gate ( display updates 3 times/sec.) The problem is that any Rpm variations will be multiplied by 10 and tend for the display to bobble. I think that you would be very pleased with the 2 digits of resolution ( 100 Rpm increments) and the gate time will help the tach keep up with the engine.

    Hope this helps shed some light.
     
  8. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    OK
    The code I created is working fine, including the math..

    Measured the signal, 66-68 Hz display 1980-2040 RPM, 116 Hz give me 3510 RPM...

    It is only refresh 1/second, in the shop I worked long time ago, my friend had digital tachometer with infrared sensor, I remember his "PRO" toll need 2-3 sec for the firs reading, and after refresh not more than 1-2 times per second.

    It would be much more accurate if you can count the flywheel toots. Some engine have one magnetic toot on the flywheel, if you can find a way to count all the toot's, that will give you very high accuracy and fast refresh.

    Steve
     
  9. Hivolt

    Hivolt New Member

    Joined:
    Mar 6, 2004
    Messages:
    15
    Likes:
    0
    Location:
    Canada
    Flywheel teeth are a good idea, there are reluctor type sensors with integral magnets, ferrous metal simply passing by the sensor will trigger it, no need for a magnetic tooth.
     
  10. Hivolt

    Hivolt New Member

    Joined:
    Mar 6, 2004
    Messages:
    15
    Likes:
    0
    Location:
    Canada
    Flywheel teeth are a good idea, there are reluctor type sensors with integral magnets, ferrous metal simply passing by the sensor will trigger it, no need for a magnetic tooth. Typical sensors are used to trigger tachometers on diesel engines, they are quite easy to get from a truck shop. The sensor are usually a couple of inches long and 5/8 to 3/4 " dia and threaded down the entire length.

    Further on your gating, 1-2 seconds is fine during constant speed, but will greatly lag during acceration.
     
  11. darior

    darior New Member

    Joined:
    Mar 6, 2004
    Messages:
    7
    Likes:
    0
    y este circuito funciona o no

    y el circuiro funciona o no
     
  12. darior

    darior New Member

    Joined:
    Mar 6, 2004
    Messages:
    7
    Likes:
    0
    this circuit its cood or not

    this circuit its cood or not
     
  13. darior

    darior New Member

    Joined:
    Mar 6, 2004
    Messages:
    7
    Likes:
    0
    this circuit its good or not

    this circuit its good or not
     
  14. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    It is working :!:

    STEVE
     
  15. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    Here is a LED tachometer, I cant find the schematic, all I can find out from the .asm header" PIC D/A Tachometer by Harbanse Deogan", don't have any copyrights info so here you go.
    I changed the 7seg pattern for common anode, all I have is CA display's.

    I draw a schematic since all I have is the ASM file.
    You have to come up with your own circuit for the input !! DO NOT CONNECT DIRECTLY TO THE IGNITION COIL !
    Tried on the breadboard, working !


    God luck.
    STEVE
     

    Attached Files:

  16. mozikluv

    mozikluv New Member

    Joined:
    Aug 14, 2003
    Messages:
    371
    Likes:
    0
    Location:
    Philippines
    lcd tach

    :D hi

    lcd is fine, but an analog tach still looks better when it comes to funtionality. try revving up and down your engine using lcd and your eyes will have a hard time following the figures. but with analog its easy reading. :D
     
  17. surfr

    surfr New Member

    Joined:
    Mar 16, 2004
    Messages:
    6
    Likes:
    0
    Location:
    Greece
    I built the led tachometer circuit and worked fine (although the leading zero, when rpm is below 1000, appears as an eight).
    My main problem is that I want to use it on my motorcycle, which has a 2-cylinder, four stroke engine with two separate ignition coils.
    So, for every two revolutions of the engine, I will pick up one pulse (spark) from any-one of the ignition coils. Is that correct?
    Is there a link I can download the original .asm file to try and modify it for my needs?
    Any extra help is more than welcome.
     
  18. tanveerriaz

    tanveerriaz Member

    Joined:
    Jan 7, 2003
    Messages:
    41
    Likes:
    0
    Location:
    Pakistan
  19. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
    You are right, below 1000 rpm the msd shows #8. I'll check why is that.
    I did not change anything other then LED patterns in the ASM file.



    tanveerriaz thanks for the link.


    STEVE
     
  20. csaba911

    csaba911 Member

    Joined:
    Jul 2, 2003
    Messages:
    242
    Likes:
    2
    Location:
    Canada
  21. surfr

    surfr New Member

    Joined:
    Mar 16, 2004
    Messages:
    6
    Likes:
    0
    Location:
    Greece
    Thanks for the help!

    Steve, I think there was an error in your display patterns.
    I corrected it.
    I played around a bit and I encountered a different problem. When using code with common cathode patterns on a common cathode display, multiplexing doesn't work properly and both numbers appear (slightly) on both digits. If I use the common anode patterns code, a 74LS14 inverter and a common cathode display, it works fine!
    I even tried changing the multiplexing timing subroutines but nothing happened.

    Following is the original code (with the correct display patterns for steve's common anode display led tachometer), can anyone give it a try and tell me if it works? I don't know, maybe it's my display!
     

    Attached Files:

Share This Page