Threshold Pot doesn't work

[h9361]

#524, not #522.

Thank you.
I had a review about the schematic, i think you right.
The DISC demod is motion and we do not need a LM393.
So, i decided to remove it and add a single simple amplifier stage with a gain pot for Iron sensitivity.
I have a similar request, is it possible to see the following schematic and check its errors?

1- For example, do you think it is better to use inverting or non-inverting amplifier?
2- Do you have any suggestion for gain of the stage (R55 and R56 values)?
3-Is the 4.7K, 100K and diode before 2n3904 correct?

Off course, i am going to test both models LM393 and the single stage.
Thank you for your supporting.

[Carl-NC]

I have no idea what kind of amplifier you need or how much gain or anything else. You really need to build the extra demod stage and see what the "iron signal" looks like before you try to figure out what to do with it. I'm pretty sure you will not be able to design a complete circuit, build it, and have it work on the first try. Build it a little at a time, and figure out the next steps as you go.

[h9361]

I have no idea what kind of amplifier you need or how much gain or anything else. You really need to build the extra demod stage and see what the "iron signal" looks like before you try to figure out what to do with it. I'm pretty sure you will not be able to design a complete circuit, build it, and have it work on the first try. Build it a little at a time, and figure out the next steps as you go.

OK. First i will build DISC part and measure its output when it detects IRON.
I will notify here, then i hope you can help me for adding the amplifier stage with sensitivity control.
I also simulated TX + preamp part on software. You can see its output on scope as following :


Channel A ( yellow) is pulse generation (0 / -5V).
Channel B (Blue) is TP8 on schematic #526.
Channel D (Green) is TP9 on schematic #526.
Do you think it is correct TP8 and TP9?

[h9361]

I have no idea what kind of amplifier you need or how much gain or anything else. You really need to build the extra demod stage and see what the "iron signal" looks like before you try to figure out what to do with it. I'm pretty sure you will not be able to design a complete circuit, build it, and have it work on the first try. Build it a little at a time, and figure out the next steps as you go.

Actually, i have doubt about connecting TP8 or TP9 to my DISC demod.
For better understanding (before making PCB), i simulated it with a pulse input (initial (low) voltage 0V and pulsed (high) voltage 5v).
You can see my pulse setting as follow:



The simulated schematic is as following:

And the its scope is as follow:

If i change my pulse as initial (low) voltage -5V and pulsed (high) voltage 0v, Scope output will be as follow:

According to the result and form of TP8 and TP9 (positive and negative preamp out), do you think which of TP8 or TP9 should be connected as input to DISC channel and sample it?

[Carl-NC]

Either one will work.

[h9361]

Either one will work.

Thank you. I will measure output voltage of DISC and will try to capture a video from ferrous/non-ferrous.
So, you will see better and help me how to figure out its final amplifier stage for blank audio.
Thank you dear carl for all supporting and your posts.

[h9361]

Either one will work.

Hello
Dear Carl
Today, i built TX and preamp part based on the following :

For first testing in my preamp output, i tested it with mono coil (500uH+680R).
Form of my Tp8 is as

And my Tp9 is as

I think my TP8 and TP9 is not correct because its pulse is showing only receiving pulse and (it is very long).
Do you have any suggestion for checking?
Do you think i should reverse invert/non-invert of 5532 (pin 2 and 3)?

[Carl-NC]

It looks like U3a is railed out, I have no idea why. Show the waveform at TP2.

[h9361]

It looks like U3a is railed out, I have no idea why. Show the waveform at TP2.

Thank you dear Carl.
I checked again and found my mistake, TX was not worked. I fixed it.
TP8 and TP9 as follows:

[Carl-NC]

That looks better.

[h9361]

That looks better.

Dear Carl
My friend is programing for adding TX sampling.
But i want to test by 74hc221 until his work is finished.
Please see attached, i tested the schematic, but the sample pulse can not locate on TX ( Can't go back any further).

I changed C15 by 1n, 100P and 10P and R29 by 100R. No result.
Do you have any suggestion for adjusting the sample pulse to TX?

[Carl-NC]

Always read the data sheet. The 74221 has 2 trigger inputs, A and B:


The 555 pulse is fed to the B input (pin 2); when it goes high (to turn off the TX) the 74221 is triggered. What you want is to trigger the 74221 on the falling edge of the 555 (which turns on the TX). You will have to feed the 555 signal to the A input (pin1) instead, and then tie the B input to the high side (ground in this case).

[h9361]

Always read the data sheet. The 74221 has 2 trigger inputs, A and B:


The 555 pulse is fed to the B input (pin 2); when it goes high (to turn off the TX) the 74221 is triggered. What you want is to trigger the 74221 on the falling edge of the 555 (which turns on the TX). You will have to feed the 555 signal to the A input (pin1) instead, and then tie the B input to the high side (ground in this case).

Thank you.
I think your means is this,

[Carl-NC]

Pin 2 goes to ground, not -5V.

[h9361]

Pin 2 goes to ground, not -5V.

Thank you.