Parking Car ElectroMagnetic Sensor

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The top IC wich is configured as a non-inverting amplifier with a capacitor in the feedback loop looks like it might have something to do with it. If the capacitor has any inductance with a high enough Q then it'll resonate at its resonant frequency which will be amplified by the second op-amp.
 
Actually, the second IC is a relaxation oscillator. And the capacitor controls the frequency. The purpose of the second oscillator is to shield the sensor (equal potentials of the plates). My question is that this oscillator has a frequency in the range of 300KHz. The capacitor is the capacitance of the sensor I hand made by myself by using two film of aluminium.
The sensitivity is only in that range. E.g. if I put my hand in front of the sensor just few kHz increases in the frequency can be noted.
Anyway, does anyone ever built a capaciflector ?
 
I built the oscillator.
It oscillates at 20Khz when no object is close to the sensor, otherwise it decrease the frequency of about 200Hz.
How can I discriminate the two tone with a PIC microcontroller?
G
 
the second IC is a relaxation oscillator.
Click to expand...
It is not a relaxation oscillator, it's an LC oscillator.

You can count the pulses using the micro and output a different tone depending on the frequency.
 
Hero999 said:
It is not a relaxation oscillator, it's an LC oscillator.

You can count the pulses using the micro and output a different tone depending on the frequency.
Click to expand...

Sorry, but I do not agree, because there are no inductance in the schematic, at least theoretically. I found the word relaxation circuit in wikipedia.

For the second problem, I am trying to learn the pic mirco!!!!
thank you anyway
 
giusepped said:
Sorry, but I do not agree, because there are no inductance in the schematic, at least theoretically.
Click to expand...

Isn't the sensor an inductor?, I would agree it's an LC oscillator, with the frequency varying as the inductance changes.
 
It's called a capaciflector as described in the early posts of this thread. Here is one link: **broken link removed**
John
 
giusepped said:
Sorry, but I do not agree, because there are no inductance in the schematic, at least theoretically. I found the word relaxation circuit in wikipedia.
Click to expand...
Nonsense, it's an LC oscillator.

A relaxation oscillator uses a switching element with hysteresis.

An LC oscillator uses an amplifier with an LC circuit in the feedback loop.

The sensor is the inductor.

The op-amp is configured as a linear amplifier, it won't work without and inductor.

Try simulating it in LTSpice.
 
Hero999 said:
The sensor is the inductor.
Click to expand...

The sensor in the project is a capacitor. See the earlier postings and the one immediately above in response to Nigel

John
 
Hero999 said:
The link doesn't work.

I don't see how the circuit could work without an inductor.
Click to expand...

I simulated the circuit many times in LTSpice and it does oscillate, as well as its implemented
counterpart.
If you stuty the circuit with Laplace transfrom it is to see that it oscillate.
The feedback on the + pin is a linear function of the output, while the forward block has
a pole.
G
 
Could you please post the file.

I have a feeling it's IC1A that's froming the hysteresis element but I don't know what IC2A does. Could it be multiplying the capacitance or comething?
 
Hero999 said:
Could you please post the file.

I have a feeling it's IC1A that's froming the hysteresis element but I don't know what IC2A does. Could it be multiplying the capacitance or comething?
Click to expand...

If you did read the early post you could understand
The IC2A is part of the capaciflector sensro, which requires that both the sensor voltage and the shield be at the same value.
Please, take a look at the technology behind the capaciflector by searching in www.freepatentsonline.com
G
 
Hero999 said:
I thought you said you didn't know how it oscillates?

If you know then why did you ask?
Click to expand...
Yes you are right. But it was an old question, when withouth any capacitor, the
circuit did oscillate. Now, I put a capacitor of 479pf on pin -, and the oscillations are clear
and understandable, moreover they are with duty cycle = 0.5.
G
 
Japanhalt


Hello!
I finished my project (the microcontroller works as frequenzimeter and self-calibrate). I also built a string capaciflector (one sensor string and one shield).
But the problem is that the range is too slow (few centimeters). You said that you built one with a range of 14 inches. Could you please give me more details? My sensor is more than 7 cm long.
Did your sensor use one level of aluminium or two?
Regards

P.S.
Moreveor, the sensor works if it is placed over a surface. If you put the sensor beside the surface the range decreases more. If I wanna mount it beside my car, I imagine that the same effect will happens.
So, maybe the sensor shown in the website is not a capaciflector but somethingelse.
 
I checked by files. That was in August, 2005. For some strange reason, I saved various etched coils made on PCB's for an inductive detector, but not the simple sensor for the capaciflector. Otherwise, I would send you a picture. I have attached a diagram of how I made my sensor. It was a rectangle about 18 X 100 mm. The stepped edges were about 3 mm each. I had to convert from it's native CAD to DXF to PDF. I hope it is still readable.

What sort of frequency shift are you seeing when an object is detected? John
 

Attachments

  • CAPACIFLECTOR2.pdf
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Thank you.
The capaciflector I built decreases the frequency when an object is approaching.
However, things change if I put the sensor behind a surface.
If I put the sensor on the table, it is very sensitive, and it can change frequency if the object is 50cm far!
If I put the sensor attached to a surface but not exposed (i.e. behind the surface) the sensitivity decreases a lot.
So, I was thinking to other sensors, like e-field sensor. I looked at some patents....
I will say to you someting in a while.
G
 
The problem is that I (we) have to put the sensor into the back of the car and not on the external surface. In this way, the sensor plate will be in touch with the chassis of the car.
....
 
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