TP4 duration

[samu]

Hi everyone and thanks for all the information,

I´m not sure my circuit is well mounted, the duration of the "valley" of the signal TP4 is less than a usec. I´ve been looking for waveforms with oscilloscope setting information but I only found it for the flyback signal. Comparing the flyback signal in the pictures from Carl´s article I suppose that this "valley" should be about 8-10 usec long.

I would appreciate if somebody tells me the correct aprox duration.

Thanks in advance.

[Qiaozhi]

Hi everyone and thanks for all the information,

I´m not sure my circuit is well mounted, the duration of the "valley" of the signal TP4 is less than a usec. I´ve been looking for waveforms with oscilloscope setting information but I only found it for the flyback signal. Comparing the flyback signal in the pictures from Carl´s article I suppose that this "valley" should be about 8-10 usec long.

I would appreciate if somebody tells me the correct aprox duration.

Thanks in advance.

Can you post a photo?
Also, what settings are you using? ... TX Pulse Freq, TX Pulse Width, Main Sample Delay, Secondary Sample Delay and Sample Pulse Width?
Have you adjusted the null-offset voltage pot correctly?

[samu]

Thank you for your interest

Here you have the pictures with the real scales. The flyback signal actually reaches about 120 volts. The pulse width is 35 usec and the frequency is 80Hz.

I must tell you that I don´t have all the circuit mounted, I´m only testing how it works so I mounted some parts in a Protoboard. Also, I´m using the first coil available (25 turns 12cm diameter). Maybe is working fine but I don´t think so, I think TP4 is very short. I only want to know what is approximate the duration of the "valley" to start looking for solutions. I don´t takes samples yet, all the circuit ahead the preamp is in project.

Is the offset calibration of the preamp important for this issue?
I used to thin that the only difference would be that the 0 level would be higher or lower.I have a lot to learn.

[samu]

Solved

Ok, if some people who knows a lot more than you about something do this that way, maybe is the correct way.

I´ve mounted the circuit "as is" and now the signal is wide enough. I posted the oscilloscope capture because maybe useful for someone else in the future.

Thank you.

[Qiaozhi]

Thank you for your interest

Here you have the pictures with the real scales. The flyback signal actually reaches about 120 volts. The pulse width is 35 usec and the frequency is 80Hz.

I must tell you that I don´t have all the circuit mounted, I´m only testing how it works so I mounted some parts in a Protoboard. Also, I´m using the first coil available (25 turns 12cm diameter). Maybe is working fine but I don´t think so, I think TP4 is very short. I only want to know what is approximate the duration of the "valley" to start looking for solutions. I don´t takes samples yet, all the circuit ahead the preamp is in project.

Is the offset calibration of the preamp important for this issue?
I used to thin that the only difference would be that the 0 level would be higher or lower.I have a lot to learn.

Have you modified the transmit oscillator, or is that a typo? The HH article states the frequency range is from 900Hz to 2300Hz, but you are using 80Hz.

[Kevco]

Something I noticed from the info provided, is his coil. 25 turns, 12 cm diameter. Doing a quick calculation of the inductance, indicates it's about 146 uH - which is about half of the target 300 uH. Lower inductance, should also produce lower flyback voltages (i.e. 120v), and shorter saturation recovery....

Kevco

[samu]

Yes, i´ve modified the transmit section. I´m using a PIC controller which is from my point of view more flexible than 555 circuit. The goal, is to adapt the hammerhead to use a PIC for timming and for detection. Is like the new versions of the HH posted. If all works OK, I hope I´ll be able to filter digitally the signal, and to make a more reliable and flexible detector.

Thank you Kevko for the information about the coil, I´ll look for a better coil.

I´ll tell you the advances (if there are any ).

Thanks again