I have a CCTV inspection camera for pipe inspections and the inline transmitter is is dead. I am trying to make my own replacement for it but am struggling a bit with the coil needed.

How do I work how many windings I need and can I do it without an iron ferret?

I need to be able to locate it through the ground using a 33KHz locator.

Hope someone out the can help me.

Cheers.

 

can I do it without an iron ferret?

I would hope so . Seriously though, can you post a schematic of the transmitter?

 

http://en.wikipedia.org/wiki/Ferret

Using the wrong word creates a really bad impression. I'm not sure we can help you without more information than you have currently provided.

 

What a shame. I was hoping to have a real life ferret in there. Apologies for my minor brain seizure. Obviously talking about a ferrite.

I have attached a schematic of what I was thinking. I was looking at using the Pic to divide the frequency of the crystal to the 33KHz and then have the FET square it out.
I haven't done the programming yet, nor determined any values in the circuit yet.

If you guys have any suggestions to the circuit as well, I am all ears.

Cheers.

 

So the 33 KHz. signal is used to locate the inspection camera. How do you access the video data?

 

The camera is attached to a video cable which is fed into the pipe.

 

Then can't you simply attach markers at known intervals along the cable?

 

What a shame. I was hoping to have a real life ferret in there. Apologies for my minor brain seizure. Obviously talking about a ferrite.

I have attached a schematic of what I was thinking. I was looking at using the Pic to divide the frequency of the crystal to the 33KHz and then have the FET square it out.
I haven't done the programming yet, nor determined any values in the circuit yet.

If you guys have any suggestions to the circuit as well, I am all ears.

Cheers.

Maybe something like this except resonant at 33 KHz.
http://www.discovercircuits.com/dc-mag/Issue-1/issue-1-exciter-circuit.htm
It would need a level shifter to get it to work with your 24 volts.
If you know the physical size of the coil we can calculate the number of turns and the capacitor size.

 

Then can't you simply attach markers at known intervals along the cable?

I'm not the OP, but I have seen these in use. Pipes aren't necessarily straight, level, or follow the bearing that you may think they do. Feed one of these 100 feet down a pipe inside your house and see if the dead reckoning approach even gets close.

 

OK. So how close do the receiver and transmitter have to be to each other? AFAIK reliable propagation at 33 KHz. is a dicey proposition given the apparent power levels of a few milliwatts. I think 1 meter might be a stretch.

 

Thanks for all your replies guys.

If you know the physical size of the coil we can calculate the number of turns and the capacitor size.

I believe the original is approx 1 inch outer diameter, 3/4 inch inner diameter and 2/3 inch long. Is there a formula I could use to calculate it if I get my hands on one to meassure?

I'm not the OP, but I have seen these in use. Pipes aren't necessarily straight, level, or follow the bearing that you may think they do. Feed one of these 100 feet down a pipe inside your house and see if the dead reckoning approach even gets close.

You are absolutely right. They can start going along the side of a house to then make a 90 degrees bend under the house.

I think 1 meter might be a stretch.

The ones I have used in the past, have been able to locate anywhere from 3-10 meters. I have been lead to believe that this circuit is out of one of these transmitters.

 

OK. I see two problems.

1. You first need to determine the inductance of the coil.
2. There are formulas that relate the inductance to diameter, length an number of turns.

Most inductors wound on a cylinder have an air core which results in low values of inductance.

 

Why do you think it is the coil? Is there 33kHz drive at the gate of FET? Is FET still good?

 

Here are a couple of calculators: You may be able to estimate the inductance from the size of your coil then pick a capacitor to make the resonant frequency 33Khz. You will probably need to 'tune" it by adding smaller capacitors in parallel with the main one to achieve maximum range, so start with a cap that is a little to small for 33Khz.

http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml

http://www.1728.org/resfreq.htm