Hi there

I would like some help making an inductive loop detector, to detect vehicles.

Something like this:
http://www.centsys.co.za/inductive-loop-detectors/flux-sa

The problem I have, if I use the coil of wire, and put a big metal object over it, I either need it to change frequency or voltage. This would then go into a PIC with A/D conversion. What type of circuit would accomplish the change in voltage so I can compare it.

Thanks

 

If you want to make your own, I found this page, and quite a few others.

 

Take a look here:
http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm
[eta]
Oops, should've refreshed before I posted; I linked to the same page that LDC3 did.

 

If I remember correctly, the LM331 is a voltage to frequency converter, that can be run in reverse, so it could be as simple as an ADC read.

You could do this with a timer, no ADC necessary and the result is, by nature, digital...

 

Here's a neat solution. Can the inductor be replaced with a large loop? Don't see why not.

 

You PIC guys are so annoying, using 7 parts to do what would require dozens in an analog design!

 

If you want to make your own, I found this page, and quite a few others.

As to LDC3 post: will I be able to get different voltages at the pin where the led is at?

Otherwise the picodetector looks quite nice too. Will have a look at both tomorrow...

 

As to LDC3 post: will I be able to get different voltages at the pin where the led is?

Actually, there should be a couple of changes in that schematic; swap the connections at 6(2) with 5(3), remove the ground from the cathode of the LED, and move the LED to between the 1K2 (1.2k) resistor and pin 7(1). Then at pin 7 (1) you'll see < 0.7v when the LED is on, and ~Vcc - Vf(LED) when the LED is off.

Otherwise the picodetector looks quite nice too. Will have a look at both tomorrow...

If you have the means to program a PIC, this would be the way to go.