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    This DIY digital tachometer for bikes uses two reed switches to get the speed information of the bicycle. The reed switches are installed near the rim of the wheel where permanent magnets pass by. The permanent magnets are attached to the wheelspokes and activate the reed switches everytime they pass by it.
    The speed is digitally displayed.

    Schematic of the digital tachometer circuit

    bike digital tachometer circuit schematic

    The tachometer works according to this principle; the pulses created by the reed contacts are counted within a certain time interval. The resulting count is then displayed and represents the speed of the bike. Two 4026 ICs are used to count the pulses, decode the counter and control two 7-segment LED display. RS flip-flops U3 and U4 function as anti-bounce.

    The pulses arrive at the counter’s input through gate U7. The measuring period is determined by monostable multivibrator U5/U6 and can be adjusted through potentiometer P1 so that the tacho can be calibrated.
    The circuit U1/U2 resets the counters.

    Since batteries are used to power the circuit, it is not practical to support the continous display of speed information. This circuit is not continously active but is activated only after a button is pressed. At least three permanent magnets must be installed on the wheel. It can be calibrated with the help of another precalibrated tachometer.

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    15 Responses to "Digital Tachometer Circuit for Bikes"

    1. Hi,

      I’m building this device for an electronics class. I had a hard time finding the CD4026 so I had to order it online. I also just picked up some random 7 seg displays from a local shop. I think they are common anode.

      I hooked it all up and the displays lit up, but didn’t mean anything. The g segment is always on and when I pass the magnet over the reeds, everything lights up. (I also did not use a resistor for the displays as it is too dim).

      Wondering if you had any trouble shooting tips. Maybe the anode display won’t work? Maybe I need to buy a cathode display? I’m kind of stuck as I’m not sure exactly what is wrong. It could be anything–including the display–as everything needs to be hooked up for it to display a speed.

      Any suggestions or help would be greatly appreciated!!!


      P.S. This is the first time I’ve ever done anything like this. At the beginning of the class, I didn’t know what a resistor was. :)

    2. do u have lay out ( protoboard ) from Electronic bicycle DIY tachometer circuit diagram
      if u have can u send to my email thats

    3. To me it looks like this: gate u1 dos not make an oscillator, just resets the circuit when powering on. The counters advance (without showing the value i.e. CE is LOW) and then, for a very brief period of time (because of the capacitor at pin 4 of gate u5) the display is enabled and you can read the counters. But hey.. what happens next? Does it count from where it left off? Who resets the circuit? Please correct me if I’m wrong and explain this circuit. And not in the way that you did so far, because that’s not really a useful explanation.

    4. I just followed your cicuit once more and found 2 other mistakes.. YOU DON’T KNOW A THING ABOUT ELECTRONICS man… So go sing to another table and stop fooling people into building your shitty experiments…

    5. raj ...naem to suna hi hoga..... says: on October 4, 2011 at 7:21 am

      adrian: tumhe to circuit ki spelling hi nahi pta hai…….read ur comment…
      bad me sab ko samajhana……chutad sala

    6. i think that it should reads only to 99 but a bike can go faster than 99 thats why it should be a bicycle trachometer

    7. please explain to me about how monostable multivibrator gets its inputs and how it operates.

    8. please send me pcb layout as possible..

    9. Hi,
      I want to assemble this circuit so before that i want to know:
      ” in which units does it shows speed(meter/sec or kilometer/hour)?”

      plz reply ASAP.

      • Jim Keith says: on October 24, 2012 at 2:46 pm

        It can be set up to indicate ft/s, M/s, MPH or kM/hr via calibration of the time base. All of these units easily fall within the range of the two digit display for bicycle speeds. If cal pot P1 has insufficient range, fiddle with the multivibrator component values to bring it into range.

        The circuit may be deficient in that it reads the correct value only once after power is applied. This needs to be corrected by adding a counter reset to the time base. Check out Adrian’s comments. I agree with his observations.

    10. can you please tell me the specifications of the reed relay used in this circuit

    11. hi..
      u have project diagram for car tachometer that can support 3 and 4 cyclinder?

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