Отправлено: 10.06.09 11:07. Заголовок: COIL

Hi !
I bought a Tektronix scope for complete this job.

First, I set the frequency to 8 KHz.
Second, I have nulled the two coils.
I have less than 1 mV. The multimeter doesn't misure less. I think is good.
Then I have selected the correct capacitance to obtain maximum signal on TX coil.
After, I have selected the best capacitance for rx resonance.
Also I have modified the phase for best sine wave.
The wires of RX coil are not inverted, they are correct comparing the phase between TX and RX.

For coil I used the coil explained for mod 02, 60/90 wires of 0.2mm diameter.

The result is that I have bad performances, many false signals and low sensibility when it works.
The Disc doesn't work.
No more of 20cm for 1 Euro coin when it works.

I have rechecked all the circuit and I have also tryed to exchange all IC and the cable without solve the problem.

I think that this coil is NOT the best coil for this project.
Do you agree or not ?

Please, can you describe a new (good) coil and frequency ?
Thank you.

Best regards,
Marco

 Отправлено: 08.07.09 12:11. Заголовок: In this screenshot y..

In this screenshot you can see the signal at the Base of transistor Q3 and Q4.


This is the signal at the Emettitor of Q3 and Q4.


Trying to null coils I have only 0.6mV at pin 3 of U1


and a little and instable signal at the output of U1, pin 6:


If I move coils in a position where they are not nulled, the signal at the output of U1 is stable but the spikes are present the same.
I don't know why.

Before to start, I have regulated R58 for zero at output having the input connected to virtual ground.
And I have selected optimum values for C7 and C8 to have the maximum signal.
I don't know how set R57 therefore I set it for maximum amplitude.
I don't know how set R26 therefore I set in middle.

Always I have only one tone with ferrous.
Sometimes I have two tones with other metals.

The maximum sensibility is about 15/20cm for 1 Euro coin.
False signal are present rarely.
Sometime is necessary to repeat the movement of the coin near coils to have sound.

As soon as possible, I will show you others images about data of coils.

Please, follow this thread !!!

 Отправлено: 08.07.09 16:14. Заголовок: This is the impedanc..

This is the impedance of RX coil (90 wires):



4.48 mH

This is the resistance of this coil:



51.3 ohm

----------------

This is the impedance of TX coil (60 wires):



2.04 mH

This is the resistance of this coil:



33.6 ohm

----------------

I am available to send any measure and/or screenshot for set the mod03m in a best way and increase performance.

Please, help me !!!