Help with building CCO?

[mikebg]

Hi mikebg.Threads in Forum , Schematics: "Popular Electronics, Feb. 1969". I'm not even realize at first.At first, I thought you had a proposal for improving the design.But later I realized that you changed so much that it would not be more CCO metal detector. In post # 39 something trying to persuade you.I have made the CCO and the CCO with a TL071 integrated circuit and capacitor of 1nF (with the help of AM radio).Work great just as the author says.Excellent sensitivity and discrimination. Is my English so bad in the rank of "drunken Englishmen," or whatever???

Maikl, the circuit diagram of CCO MD attached in mentioned post # 39 has many disadvantages. They are described in that thread (post #48 etc). What frequency shows your AM radio?

[nabiul]

Yes yhl, but you should create 4.5V operating point in output using two resistors for bias. Post me an email with attached your circuit diagram, to show you the correction.

Where would these resistors go?

Could you post the modified schematic here? The original schematic is available in the first post.

It seems like a much better idea than carrying a 2.5 pound lead acid battery.

[maikl]

Maikl, the circuit diagram of CCO MD attached in mentioned post # 39 has many disadvantages. They are described in that thread (post #48 etc). What frequency shows your AM radio?

Hi mikbg. I am referring to post # 39 here on this subject and not the one "Popular Electronics, May. 1969". But there is no language barrier seems to do in the matter.This design has excellent sensitivity but for our purposes is the Eastern European shallow and not deep enough.In your opinion this design has flaws? Please give your suggestion and set the whole pattern.

[mikebg]

Hi mikbg. I am referring to post # 39 here on this subject and not the one "Popular Electronics, May. 1969". But there is no language barrier seems to do in the matter.This design has excellent sensitivity but for our purposes is the Eastern European shallow and not deep enough.In your opinion this design has flaws? Please give your suggestion and set the whole pattern.

Maikl, the schematic in post #39 here is TARSOS. You ask my opinion for TARSOS?

[mikebg]

The schematic in my first post. The one in post #12 is a beat balance detector, not the CCO.

Nabiul,
The disadvantages of circuit diagram in post #1 are:
1. Too large supply voltage. If using HCMOS inverter (like HC04) instead 4069, the circuit can be powered by 2 x AA rechargeable cells (2.4V battery).
2. Negative feedback via R is too weak, so the input resistance of inverting amplifier is not zero. This decreases Q factor of tuned circuit L2-C1 and increases bandwidth, ie the preamp generates more noise.
3. The 500KHz operating frequency is too high.
4. The capacitance of the capacitor C2 is too large. You can increase the number of turns on L2 and this the sensitivity, if using smaller capacitance for C2.
5. IC1a is loaded unduly with DC current in operating point. Instead of R2 must be connected a capacitor.
6. Is not intended a control knob to adjust the sound frequency.
7. Is not intended to suppress the GND signal using a second RX coil, connected in series to R2.
8. Remains not used 3 inverters of IC1. They can be used to replace the action of IC2 and connected in parallel to IC1a to increase TX current.

[nabiul]

Yes all those things are true and the circuit could be greatly improved, but I've already built it and I need to know how to fix it.

From my understanding, the op amp amplifys the difference between the non inverting and inverting inputs by the internal gain, and at high supply voltages, the difference between them becomes smaller and smaller. So a quick solution to this would be to put a voltage divider to ground with a variable resistor on one of the inputs?

For my next metal detector, I'll try to redesign it.

[mikebg]

Nabiul, try this:

[nabiul]

Is that particular diode necessary or can it be any old diode?

I've got a ton of 200v 3A diodes.

[mikebg]

Is that particular diode necessary or can it be any old diode? I've got a ton of 200v 3A diodes.

Nabiul, if your hobby is electronics, you should buy a ton of diodes 1N4148. They are very small and the most cheap diodes for signal processing.
However I posted an idea only. Since for me this is a BAD CIRCUIT, my advice is to try something better, like HOUNDOG. Here is an idea for modernisation of HOUNDOG.

[yhl]

Dogs can detect how far the money?

[nabiul]

Nabiul, if your hobby is electronics, you should buy a ton of diodes 1N4148. They are very small and the most cheap diodes for signal processing.
However I posted an idea only. Since for me this is a BAD CIRCUIT, my advice is to try something better, like HOUNDOG. Here is an idea for modernisation of HOUNDOG.

My hobby is whatever I happen to be interested in within any 2 week time span.

What does it mean by audio processor?

[Krzysztof]

Greet Nabiul.
Patern Mikebg has small mistake (short-circuit between "lm" and "rg"). These dots near coils (L2A - L2B) will be inconvenient also.
After making on table this and you will hear connecting to some amplifier all, but not artefacts (money).
This requires the stable technique, wise PCB and a lot of time.
I think, that more quickly and cheap for You this to buy new, cheap MD Chinese and to test in terrain one's seeker's abilities.
Every construction MD is tong - term here, a lot of tests require and it costs unfortunately always.
Necessary knowledge is also, seizure, experience; electronic with school this for little.
I with whole respect greet Chris.

[nabiul]

Yes in the long run it might be cheaper to just buy one, but I like trying to build things rather than actually using them.

[Krzysztof]

This was had to teach yet a lot of. You and I.
Best regards Chris.

[maikl]

Maikl, the schematic in post #39 here is TARSOS. You ask my opinion for TARSOS?

Hi mikebg. You have not given me your opinion on TARSOS.