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# Help me implement a speed sensor

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#### neiji

##### Newbie level 2
I want to implement my own speed sensor which will be used to monitor the

speed of a 3Vdc motor of an electric car. Any idea on parts to be used are

welcome, as i have no idea how to implement it.

rc wheel speed sensor

U can go for tachometer type design which will measure pulses per seconds.One pulse= One revolution

Re: Speed sensor

All cars with electronic fuel injection and static ignition systems use a teeth wheel. This component in conjuntion with a inductive sensor are used to see the engine position and rpm, this teeth wheel generally has 36 - 1 (in Ford cars) or 60 - 2. This means that these wheels has absentee teeths for reference point.

I think that you can buy a conjunt of sensor and wheel from any car and use it to your purpose.

If you use this, I have a circuit that I use to get the inductive signal from this sensor, and I can send it to you.

Speed sensor

i'm using hall effect sensor to measure wheel speed of an rc car.output of the sensor is fed into a counter, then into a microcontroller, PIC16f877A. can someone help me with the programming to calculate the speed?
thanx

Re: Speed sensor

:!:
just measure the rpm of the wheel with the help of the rpm reading i think u can calculate the speed of the car

Re: Speed sensor

Two choices, both simple algoritmes, not so simple to implemente.

RPM = rotation per minute or RPS = rotation per second

Choice one:
mesure the time between pulses (T in mili seconds), you already know the perimeter of the wheel (L in centimeters) so
Velocity = L / T in cm/ms, for km/h just do the conversion

Choise two (in my opinion better):
count the number of pulses in one second (C in rps, assuming just one sensor), again you already know the perimeter of the wheel (L in centimeters) so
Velocity = C*L in cm/s, for km/h just do the conversion

dont forget that if you are using more that one hall sensor in the same wheel then
rpm = number of pulses / number of sensors per minute
rps = number of pulses / number of sensors per second

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