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How to measure the rpm of a car motor from the ripple battery?

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mlara

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hello,
I want to to measure the rpm car motor from the ripple battery. These ripple is related with the rpm motor.
I think to use a hp filter for to amplifier the ripple and cut the continuos signal.
I hope that you Know the best solution

thanks, and you excuse me for my english level. I'm Spanish
 

motor pulse generator circuit

Hello mlara

Strange idea....
Is your only option?
best regards
 

rpm to voltage conversion circuit

Yes,
there is other solution with a frecuency-voltage converter (LM-2917). But I need a ac signal (voltage) and that signal is in the car's coil and i need measure the rpm from the battery

Thank you
 

how to measure rpm of a motor

Hello mlara,
There is another option with out getting any AC signal from the motor coil but using of a small magnet, reed switch and FVC (frequency to voltage counter) and of course the processing circuits to convert the frequency to RPM . Actually, I had a project three years ago that did measure motor RPM. Are you interested. but I still have to dig up where I put the design

regards
 

rpm messure circuit

ok neoaspilet11,

of course that interests to me, if you find me you communicate it please.

Thank you very much by everything
 

measuring car rpm from battery

The circuit diagram is on the attachment. There are actually two solutions for your problem. But the basic electrical interface of your rotating motor and your circuit is the generation of pulses. This can be done by attaching a small magnet to any rotating part of the motor and a reed switch (not attached to the rotating memeber of teh motor). The reed switch will be closed everytime it encounters a strong magnetic field. and this magnetic field is generated by your magnet attached to the rotating member of the motor.

1.) The first solution is described below. This is what I did before. After the pulses are generated, it is converted to volatge and the volatage is feed into an ADC. The ADC is feed into a computer for processing the data. you need to calibrate yopur software to get the correct RPM on the voltage converted by the ADC.

2.) The second solution I think is using a microcontoller. You feed in the genertaed pulses directly to tne MPU and have the MPU programmed to measure the time duration of the pulses which can be translated to RPM. Although this will require a quite programming challenge on your part.

Hope this helps.







Speed Sensor
This sensor is also custom built. It will give proportional voltage for a proportional change of speed. Reference voltage is also set for a reference speed (normal speed). The reference voltage will be 0.75 Volts assumed to have a speed of 50 cm/s. And the maximum voltage for the maximum speed is 5 Volts.


Fig 3 – 3. Speed Sensor Circuit

The following are the major characteristics of the speed sensor.

1. Basically the sensor is composed of the three main circuits: the pulse generator circuit, the frequency to voltage converter circuit, and the voltage limiter circuit. The circuit uses the +5V and the +9V as its supply voltage, which has an output current of less than 135uA. The sensor has minimum power dissipation enough not to drain the battery supply.

2. The wheel has four magnets spaced equally on its outer part. These magnets were used to actuate a single “normally open type” reed switch connected to an schmitt-trigger debouncing circuit. This circuit was designed to produce a clean output pulse in response to the switch’s closure.

3. The frequency of the input pulse was converted into a DC voltage value in the frequency to voltage converter circuit. The circuit was designed that the minimum and maximum speed of the water are calibrated in equal resolution based on the computation. It is chosen and assumed that the river has a minimum speed of 0 m/s that is equal to 0V output. The maximum speed assumed to be 4 m/s has a voltage value of 5V considered to be the maximum speed.

4. The voltage limiter circuit was designed to limit the voltage output not to exceed 5V. This is because the reference voltage for Analog - to - digital conversions is 0 to 5 Volts only.

5. The level sensor also includes switching circuit for the battery supply to be recharged. The charger circuit is separated for the circuit’s simplicity.


Pulse Generator Circuit
The pulse generator is composed of RC charging/discharging circuit and a Schmitt type inverter as debouncer switch. The capacitor is charged with the input voltage when the magnetic switch is open and discharged when the magnetic switch is closed.


Fig 3 – 4. Pulse Generator Circuit

1. The charging circuit is designed to have a time constant of 1 millisecond. At the moment the magnetic switch is open it will take 1.83 millisecond for the capacitor’s stored voltage to drop or discharge to 0.8 volts – the voltage level recognizable as logic zero for the input of the Schmitt trigger inverter.

Equation 3 – 1 Vc (volts) = V0e-t/RC
T = -RC ln (Vc/V0)

Substituting Vc = 0.8 Volts, V0 = 5 Volts and time constant = 1 ms, t can be computed as 1.83 ms.

2. The voltage decay from 5 volts to 0.8 volts will interpreted as logic 1 input by the Schmitt trigger inverter. Input voltage below than 0.8 Volts will be interpreted as 0 by the inverter.

3. The capacitor quickly discharges when the magnetic switch is close. The discharge time is quick because from Equation 3 –1, the exponential becomes zero when R is zero. The discharge time is assumed to be in microsecond range although there is no proof for this.

4. The capacitor charges to 0.8 Volts in 1.83 ms upon close - to - open transition of the magnetic switch. Therefore the time interval of two closures of magnetic switch must not be less than 1.83 millisecond.
Frequency to Voltage Conversion
The function of FVC is to convert input pulses of the Pulse Generating Circuit to voltage. The main element use is the FVC IC – LM331 (from National Semiconductor).


Fig 3 – 5. Frequency to Voltage Converter Circuit

1. The circuit above is the typical application of LM331 as frequency – to voltage converter as provided by the manufacturer (National Semiconductor).

2. The Rt resistor is computed such that at maximum input frequency 34 Hz the output voltage is 5 volts. The maximum input frequency is chosen deliberately and relatively small because the speed the sensor is measuring is relatively low speed. It is arbitrarily chosen that the sensor can sense up to 4 mps speed.

Equation 3 – 2 Vout = fin * (RL / RS) *1.9 * (1.1 Rt * Ct), Volts

Where RS is the total resistance of the gain adjustment. Reversing the calculations, Rt is found 1.196 M. The closest commercially available value is 1 M.











Voltage Buffering and Limiting
The voltage limiter is necessarily connected to the output of the speed sensor because the maximum allowed voltage inputted to the Transmitter processing Module is only 5 Volts.


Fig 3 – 6. Voltage Limiter

1. The zener diode acts like an open circuit when the voltage across the zener diode is less than the zener voltage. The output voltage therefore is the voltage division of the input voltage.

2. The zener diode acts like a voltage source with voltage equal to the zener voltage if the voltage across it is greater than the zener voltage. Therefore the output voltage is limited only up to the zener voltage.

3. The zener diode is chosen to have a zener voltage of 5 Volts. Commercially available zener diodes that have zener voltage close to 5 Volts are 1N5230B (VZ = 4.7 Volts) and 1N5231B (VZ = 5.1 Volts).

4. The load resistance is the resistance of the input in Transmitter Processing Module.

5. The output voltage of the frequency to Voltage converter is buffered so that it will not load to the next network stages and the input current to the ADC is small.








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