# Automotive Speed Limit Indicator Circuit

In our earlier content we certainly have found out widely concerning the ICs LM2907/LM2917 which can be simply frequency to voltage converter ICs, and are preferably relevant in all such appropriate fields. Here we observe how the same chip can be utilised to create a vehicle speed limit alarm circuit.

Speedometer Image

In accordance with the described instance the IC could be utilized to make a basic speed limit switch circuit which often might be used in vehicles for detecting over-speeds and progressively alarming or stopping the vehicle from passing the set dangerous mark.

As revealed in the below diagram a single LM2917 is sufficient for designing the suggested speed limiter circuit together with a few external passive components.

Talking about the diagram, the input pin#1 obtains the signal from the wheels of the vehicle by means of a magnet and pickup coil arrangement or by means of a Hall impact sensor circuit.

You might signify this post for understanding the simple set up of the wheel and pickup coil in the presented diagram.

The feature is fairly a lot very much like the earlier spelled out speedometer circuit working:

The utilized speed info by means of pulses matching the revolving wheel count is imagined by the contrary opamp whose inverting input is referenced to ground for highest sensitivity.

The output out of this opamp is given to the subsequent that may be the charge pump stage to blame for tracking/holding/boosting the information through a gradual DC.

This work depends especially on the value of C a pin#2 of the IC.

The above information and facts are more heightened and compared by the succeeding opamp and common collector transistor phase.

The output is shut down at pin#4 of the IC via the emitter of the internal common collector transistor.

According to the formula, the speed limit alarm could be set and determined by utilizing the formula:

f(in) = R2/R1+R2 x 1/RC

Once the set limit is attained, the IC picks up it and generates a high logic at pin#4 which is equivalent to the supply voltage of the circuit.

This high logic can be utilized for appearing an alarm, deactivating the engine or for initiating further comparable preventive steps.

A standard execution of the above design may be observed right here diagram. Right here the load or the speed limit warning alarm is linked at the transistor collector pin#5 output rather than pin#4 as narrated in the above spot.
The collector load configuration presents the benefit of better current acquire enabling a greater wattage device for example a relay or an alarm to be instantly utilized with the circuit.