I would like to build a loop detector.

G McMurry

I would like to use the basic stamp to sense the presence of a mass of metal. This would be similar to how a "loop detector" works that you drive your car over in a driveway.

Has anyone tried this? I need a simple circuit that can be done on a small amount of PCB real estate.

Greg

Mike Green

Here's a thread on the subject.

G McMurry

Not quite what I am looking for but I bet I can learn something... I want to build a single loop like at a traffic light, not a metal detector.

This type of design is a bit beyond my pay grade. Maybe someone here can lead me to some solutions.

Here is a schematic of what (I think) I want to do.

http://www.gregssandbox.com/pics/electromagnetic_train_sensor_V001_.jpg

I need to make a loop approximately 6 X 8 inches. I can use any number of turns but I think I need to use teflon wire. I want to direct bury this under a train track that is 7.5" wide.

Then I would build a low Z oscillator that drives the loop at some frequency (that I need to calculate) through the 100 ohm resistor.

My circuit then looks at the voltage that it takes to get the loop to resonance. The diode and the 2uf cap rectify the voltage to give me some DC to measure with RCTime. I measure that voltage with the basic stamp and fine tune the oscillator until it peaks. Then I read the voltage using the BS2 rctime and watch for changes that happen when I move a metal train over the loop.

Make any sense?

How do I figure out what frequency to start out with on my oscillator? Trial and error with my function generator? Maybe?

Is this a stupid idea?

Greg