Menu
What's new
Find's Treasure Forums

Welcome to Find's Treasure Forums, Guests!

You are viewing this forums as a guest which limits you to read only status.

Only registered members may post stories, questions, classifieds, reply to other posts, contact other members using built in messaging and use many other features found on these forums.

Why not register and join us today? It's free! (We don't share your email addresses with anyone.) We keep email addresses of our users to protect them and others from bad people posting things they shouldn't.

Click here to register!

Need Support Help?

Cannot log in?, click here to have new password emailed to you

Help with PI

A

Anonymous

Guest
I'm a student of engineering and I'm finish a project of PI detector that I got from Carl and I change some things for adapt to interface with a PIC microcontroller.
It work verry well and good distance, but I have problem with the drift termico. I have problem with the diode the limit the signal from the coil and I test a lot of kind of diode without success. If I warm and cold the diode separate the analog output change 1V.
If you could help me I would like to know that I can doing of wrong ?
What kind of diode is good to use in this case ?
I use amp op OPA132 how fist gain and OPA2132 how integrator and the sourse of amp op is diferente from the 5V of the PIC microcontroller.
I checked with the scope gat FET and all the circuit.
Best Regards.
Gilmar Ribeiro de Oliveira.
 
Hi Gilmar,
I've never had problems with the limiting diodes, and invariably use the 1N4148. Dual sampling of the front end amplifier should cancel any dc drift anyway, provided the integrator is properly balanced. I have not tried an OPA132 but notice that it is a Fet input amplifier. What determined that as a choice?
Eric.
 
Hi Eric,
Thanks for help.
I'm not use the two sampling, so I think is this my problem.
What distance between two sampling that I can use ?
I choose the OPA132 because of the low drift termical.
Thanks,
Gilmar
 
Hi Gilmar,
Two samples are definitely the best. Also cancels out movement of the coil in the earth's magnetic field. You could try a blocking capacitor between the OPA132 and the sampling gate. Say a 10uF tantalum for a start. This will block any dc drift on the opamp output. However it will not get rid of low frequency signals as effectively as a dual sampler does.
Eric.
 
Hi Eric,
Thank you very much for your help, I have work in this problem for months, without success.
Now I understand the function of the two sampling.
I'll make this in my circuit.
I would like if you can send me a schematic for I take a look in the two sampling.
Thanks,
Gilmar
 
Hi Gilmar,
Have a look at Carl Moreland's Hammerhead schematic. IC7 a and b are the two sampling gates which connect to IC8a, the differential integrator. This subtracts and averages the two sampled signals, and any dc offset from the front end circuitry will cancel out.
Eric.
 
Hi Eric,
Thank you very much your help.
I'll test the two sample and I return to with the resulted
Gilmar
 
You must log in or register to reply here.
Top