Brake/Roller RPM sensors


YourDyno needs as a minimum one brake RPM sensor per independent brake. So if you have 1 brake you need 1 RPM sensor that measures the speed of that brake. If you have two brakes that are physically interlinked, you need only 1 RPM brake sensor and if you have 2 independent brakes you need 2 brake RPM sensors. For an inertia dyno you need 1 roller RPM sensor. 

In addition (but not instead) the Engine RPM can be read. This will provide automatic calculation of gear ratio. Options for Engine RPM are described here

Brake RPM sensor considerations

YourDyno RPM sensor is recommended as a low cost, proven sensor with shielded cable. 

But any sensor that provides a 0-5V square wave signal will work. VR sensors do not work directly, but can be used with an interface board that converts the signal to 0-5V. For example this one (select the 5V version).

YourDyno needs 200 trigger pulses per second as a minimum to work optimally. This means a trigger wheel is necessary. The RPM sensor senses the teeth on the trigger wheel, and produces one pulse per tooth. There are a few rules for the trigger wheel.

Trigger wheel mechanical/material considerations

The trigger wheel must be of a ferrous metal (iron or steel).

The distance between the teeth on your trigger wheel must be perfectly regular, otherwise you will have noise. You must also avoid eccentricity in the trigger wheel, as it will cause the sensor to trigger at slightly different times as the wheel spins.

Here is the spec for the mechanical dimensions of the wheel.

How many teeth do you need
As a general recommendation, choose a trigger wheel with enough teeth to give at least 200 pulses per second at the RPM you care about. This is because YourDyno needs 2 pulses to produce 1 result, so unless you have at least 200 pulses per second you will not get 100 updates per second. More importantly brake performance and inertia accuracy will be reduced.

There is no hard limit to the maximum number of pulses per second, but it is recommended to stay below 6000.

How to get hold of a trigger wheel

YourDyno sells a 30 tooth trigger wheel, suitable for most roller and hub based dynos. Some modifications will typically be needed to fit it to your brake/roller axle.

RPM Trigger wheel –

NOTE: A typical crankshaft ignition/ECU timing wheel does not work! They are made with one or more gaps in the teeth in order for the ECU to know the absolute position of rotation of the crankshaft. YourDyno expects no gaps, and such a wheel will cause a large noise in the RPM readings.

Using an Encoder

Using an encoder for the brake RPM is also possible if you do not want to use the standard YourDyno RPM sensor. Keep the pulses per revolution below 250 or so and choose a open collector type encoder (i.e. an encoder that needs a pull-up resistor to work). YourDyno has a built in pull-up resistor to 5V. 


YourDyno has an internal pull-up resistor to 5V for the Signal input. Some setups with long RPM wires may need an extra pullup on previous hardware versions (Rev AD and earlier). Add in that case a 1kOhm resistor can be added between 5V and the RPM Signal input (ensure with a multimeter that you really connect to 5V, it MUST not be higher). 

















Last updated byJostein on February 9, 2022


  1. Lars
    January 20, 2020 @ 6:37 pm

    What’s the specified air gap? Could not find tgis in this post.


    • admin
      January 27, 2020 @ 10:40 pm

      Air gap is 1mm or less.


  2. John
    June 26, 2020 @ 7:02 pm

    How long is the cable that comes with the RPM sensor?


    • admin
      July 2, 2020 @ 8:01 pm

      Hi, it is 3.5 meter.


  3. Gasssed
    February 13, 2021 @ 10:27 am

    Where do we input the trigger wheel details when setting up a new dyno?

    I’ve made use of the DXF and had one laser cut, installed as per instructions etc.

    Have an rpm reading, but it’s obviously off, so need to adjust/set


    • admin
      February 13, 2021 @ 11:02 am

      Hi, you set the pulses per revolution in RPM Setup in the Run window. Second tab. After that you need to set the gear ratio and you are good to go.


  4. David
    March 2, 2021 @ 10:40 pm

    I Dont know if I understood well the number of teeth needed.
    If I wan to measure 300RPM I need 200pulses/(300rpm/60)= 40 teeth?


  5. DAVID
    March 4, 2021 @ 10:17 pm

    ii am not sure of the minimum number of teeth that we need. You say that As a general recommendation, choose a trigger wheel with enough teeth to give at least 200 pulses per second at the RPM you care about. But if you want to measure 350 RPM you’ll need 200/(350RPM/60)=34.28 TEETHS. Is it ok?
    But do you have a maximum number of pulses ? I think the maximum could be limited by the CPU frequency


  6. admin
    March 4, 2021 @ 10:38 pm

    You calculation is correct. The max limit is very high. Stay below say 5000 pulses per second.


    • David
      March 5, 2021 @ 8:08 am

      Thanks for your answer.
      If I have a trigger wheel that produces less than 200 pulses (like 100 for example). Am I able to measure the RPM or it would be impossible?


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