sensor interfacing circuit problem

[zawminoo]

Hi,

The input of circuit is sine wave (0.6V~40V) and output is about 5V square wave.
This circuit have no problem for low voltage and low frequency.

When give high frequency ,it can't go down to zero level.
What should I change this circuit to remove this problem?

 

[angelote]

Your OPAMP is in saturation. To exit from saturation, the OPAMP needs a time. If you increase frequency, you shorten the period of the signal, and the OPAMP have no time for saturation recovering. Also, if you increase voltage, saturation is stronger, and the OPAMP needs more time for recover.

To solve this you can use a faster OPAMP, or change the circuit to use a comparator.

 

[Ahmed Ragab]

Your post says that this is a "Sensor interfacing circuit" but I actually don't know where is your sensor !!!
If I'm correct then I guess the sinusoidal function generator represents the sensor, that's why you mentioned it's voltage changes from 0.6V to 40V.
The only thing I couldn't figure is how may the sensor change with a frequency of 100Hz?! It's quite a large value, I mean sensors don't change there outputs that fast, that's why you're using LM324 instead of any other Op-Amp.

Something is missing, I guess. Try to be more clear about the functionality of this circuit and I'll do my best to help ISA.

Salam for now.

 

[zawminoo]

Hi,

Yes,The sinusoidal function generator represents the sensor.
It is crankshaft position sensor or Variable Reluctance Sensor.

The VRS sensor in the Honda F1 engine generates a 0.6V signal at cranking speeds, and a 40V signal at 6000 RPM.

The VRS interface circuit is designed to translate the analog sinusoidal signal from the engine’s crankshaft sensor into a square wave that can be recognized by the microcontroller. The circuit converts a sinusoidal signal that varies from about 0.6V at 6.7 Hz for cranking speed, to greater than 40V at 166.7 Hz for 10,000 RPM into a square wave that is either 0V or 5V over the same frequency range.

The VRS interface uses a non-inverting operational amplifier (Op Amp) circuit to condition the crankshaft signal. I chose to use an LM324 Op Amp for this circuit since it operates with a single power supply, eliminating the need for a negative power supply, since the microcontroller requires only positive voltage inputs. The two 10V Zener diodes (D1 and D2) are configured as a Zener limiter to isolate the Op Amp from the higher voltage signal as engine speed increases. The Schottky diode (D3) prevents the input of the Op Amp from going more than 0.3V negative. The Op Amp has a +6V supply so it will have a +5V output at saturation (due to a 1V internal drop in the Op Amp). The Op Amp has a gain of (R3+R4)/R3 which is 21. This amplifies a small signal of 0.6V to 12.6V, and since the Op Amp saturates at 5V, its output is 5V.

But, At high frequency, I have above problem.
If it's need to change opamp, What does opamp suitablr?

Please give your comments and suggestion.

Zaw

 

[Ahmed Ragab]

If I'm understanding your application correctly then you want to sense the speed of the motor through the VRS output. The VRS output gives a sinusoidal signal that varies in both amplitude and frequency based upon the speed of your motor.

If I'm correct, then why do you use this circuit the first place? You're trying to generate a square wave of variable frequency according to the frequency from VRS??
Instead work with the amplitude of it.
to read this into your controller then all you need is an analog to digital converter, you'll have to rectify the sinusoidal signal and then apply it to a smothing signal, then read the analog output formed, it will be converted into a digital byte which can be read easily to your controller.

Tell me if I'm loosing something here, I might be wrong.

salam for now.

 

[nikhilele]

why don't you use optical coupler to interface it with your controller or processor.
just amplify the low level sensor ouput to something that can drive led and use zener limiters to drop higher voltages

 

[zawminoo]

Hi...

This sensor will sense the speed of automobile engine.
There are a wheel with teeth at crankshaft of engine.
Nearly same as following sensor (at picture).
Other sensor(optocouple) can use for this but I think this more cheaper.

ADC is not need because I will use PIC16F877.

Welcome any comment & suggestion.

 

[zawminoo]

Hi everybody,

I still waiting your suggestion.
Please give me some advices or comments.
I want a circuit that better my circuit or what should I change my circuit.
Can you give another circuit.

Thank!
Zaw

 

[GrandAlf]

Since you only seem to need the pulse rate rather than amplitude, why not a high speed optocoupler with shmitt logic o/p. You may need a transistor pre amp to get the voltage swing a bit higher to overcome the VD of the opto led.

 

[Ahmed Ragab]

Why don't you try using the LM382 instead of the one you're using ??
I know it's an audio amplifier, but that means it will work for even larger frequencies than the one you're working with.

Just an opinion, I'll try to work something better out soon for you.

Salam for now.