Threshold Pot doesn't work

[Carl-NC]

OK, I see. As long as the circuit isn't actually oscillating then it might work. All I can say is try it and see.

[h9361]

Is L1 the RX coil? Why is it part of an oscillator?

this is an FM receiver, L1 and C2.
This type in RF is called super regenerative receiver.
For RF, oscillator is used for Easier content extraction.

Do you think the schematic is true?

[Carl-NC]

Is L1 the RX coil? Why is it part of an oscillator?

[h9361]

Probably that will work. It looks to me like the 4060 will provide a 125kHz square wave.

Hello
Dear Carl
I hope you are passing good days.
Now, i am working about a new idea, RF metal detecting.
This is a primary idea and i am playing and testing it.
For testing, i have designed a simple RF receiver in FM modulation ( my TX frequency is 300mHz with a pulse 400Hz audio as input).
Please see it, if possible. Do you see any error or any suggestions for improvement?
My main purpose is that i detect any small changing on audio tone (400hz).
since my transmitted audio is 400hz, i used 220p for 700hz filter.
Its final output goes to lm386.
Thank you.

[Carl-NC]

Probably that will work. It looks to me like the 4060 will provide a 125kHz square wave.

[h9361]

I don't see why not.

Thanks.
I tried to calculate pulse width and duty cycle of 4060-output, my calculation is 8us and duty cycle is 50%.
Is it true? because i want to set this adjustment on 7555 output.

Please see it, do you see any error to this replacment (7555 to 4060)?

[Carl-NC]

I don't see why not.

[h9361]

Yes, that's what the documentation says: you should adjust R18 before you install R5 and the coil. You do not need to remove IC11 or IC12 for this. You only need to ground IC8-pin1 for adjusting the demod offset, and this is an adjustment that is not critical.

Hello
Dear Carl
I hope you are in a good health.
Please see the attached, it is a simple schematic metal detector.
I need to use it in a specific project for testing but i want to replace its 4060 with simple 555 (7555) timer.
Out of the 4060 is pulse, can i replace it with 7555?

[Carl-NC]

But problem is that you can not see a static value in TP4!
So, you can not adjust the R18 in correct point.
For this, you have to stop Pulse frequency and two samplings pulse (removing 555 timer and 74hc221 ICs).
Then you must connect out of IC8 (pin1) to ground!

Yes, that's what the documentation says: you should adjust R18 before you install R5 and the coil. You do not need to remove IC11 or IC12 for this. You only need to ground IC8-pin1 for adjusting the demod offset, and this is an adjustment that is not critical.

[eduardo1979]

Hi h9361.
Why don't you divide the preamplifier circuit into two stages? This way you'll get a higher sampling rate in the first amplification stage and better offset if you use a suitable operational amplifier. I recommend using an OPA1612AID. It's a very good operational amplifier. It's a bit expensive, but I think it's worth it. Geomax is right; you should post your final schematic here on the forum so you can get much more help from other forum members.

[h9361]

Hi h9361,

I don't quite understand your last post. Perhaps you have little experience with electronics and PCB projects? It seems you're trying to start in the middle of an existing project and adapt it to your needs/project. That's the wrong approach. I would tackle your project as follows:

1) Create a completely new schematic based on the Hammerhead circuit with your modifications using your schematic editor.
2) Check and validate every part of your schematic before proceeding. You can post your circuit here and ask the community for advice if you're unsure about anything.
3) Once your schematic is complete, the first thing you should do is choose the enclosure for your detector project before starting the PCB design.
4) After selecting the enclosure, draw the outline of the PCB that will fit inside it. Pay attention to the mounting holes, the position of the controls, and ensure that all components fit on the PCB.
5) Once steps 1 through 4 are complete, create the printed circuit board (PCB) in your PCB editor with dimensions that fit your chosen enclosure. Place the components and route the traces.
6) After finishing routing your design, create Gerber files and send them to the PCB manufacturer in China, or etch the PCB yourself.
7) Once your board is finished, populate it with components, test your circuit, and begin programming the microcontroller.

Dear GeoMax,
For adjusting R18 in correct point, we need to connect the DMM on TP4 (HHD PCB).
The Correct value for R18 is Zero volt in TP4.
But problem is that you can not see a static value in TP4!
So, you can not adjust the R18 in correct point.
For this, you have to stop Pulse frequency and two samplings pulse (removing 555 timer and 74hc221 ICs).
Then you must connect out of IC8 (pin1) to ground!
In this mode, you can see a static value in TP4 and you can easily adjust R18 for 0V in TP4.
After adjusting, you can add the ICs in his locations and remove the conection of pin1 of IC8 to ground.

[GeoMax]

Hi h9361,

I don't quite understand your last post. Perhaps you have little experience with electronics and PCB projects? It seems you're trying to start in the middle of an existing project and adapt it to your needs/project. That's the wrong approach. I would tackle your project as follows:

1) Create a completely new schematic based on the Hammerhead circuit with your modifications using your schematic editor.
2) Check and validate every part of your schematic before proceeding. You can post your circuit here and ask the community for advice if you're unsure about anything.
3) Once your schematic is complete, the first thing you should do is choose the enclosure for your detector project before starting the PCB design.
4) After selecting the enclosure, draw the outline of the PCB that will fit inside it. Pay attention to the mounting holes, the position of the controls, and ensure that all components fit on the PCB.
5) Once steps 1 through 4 are complete, create the printed circuit board (PCB) in your PCB editor with dimensions that fit your chosen enclosure. Place the components and route the traces.
6) After finishing routing your design, create Gerber files and send them to the PCB manufacturer in China, or etch the PCB yourself.
7) Once your board is finished, populate it with components, test your circuit, and begin programming the microcontroller.

[h9361]

Hi h9361,

Yes, you can remove it. Simply leave the circuit board unpopulated and bridge the three holes of potentiometer R23 with a wire jumper.
Why do you want to remove the potentiometers? They are very helpful for correctly calibrating the circuit.

PI-Polones:
I don't know the exact frequency. But I estimate it will be somewhere between 300 Hz and 600 Hz.

Thanks dear GeoMax
I want to make SMD PCB.
As you probably know, for adjusting R18, i have to remove IC5, IC8, IC11 and IC12 and then connect pine 1 of IC8 to ground.
In this case, i can adjust R18 based on voltage of TP4.
Problem is on SMD model and we have a limitation. I can not remove this ICs from SMD, so i can not connect the pine 1 of IC8 to ground.

[GeoMax]

Hi h9361,

Yes, you can remove it. Simply leave the circuit board unpopulated and bridge the three holes of potentiometer R23 with a wire jumper.
Why do you want to remove the potentiometers? They are very helpful for correctly calibrating the circuit.

PI-Polones:
I don't know the exact frequency. But I estimate it will be somewhere between 300 Hz and 600 Hz.

[h9361]

Hi h9361

Thanks for the explanation. I didn't realize the depth difference was so significant with large coils and single sampling. Now I understand why guys from the Middle East and North Africa always rave about the PI Polones and say it "goes deep". The PI Polones is also a single-sample detector.

Dear GeoMax
Do you know at what frequency guys from the middle east and north Africa use Polones?