What is the value of the capacitor?

[NOriyuki]

I am new to electronics and need your help. I am trying to build a metal detector from this website. I am confused because some of the components do not have units of value listed. Has anyone built this metal detector? I am unsure about C1, C2, C4, and C6. Do you think the units of these numbers are "nF", "pF", or "uF"?

http://maker.pro/storage/xdlOtSv/thu...WoDTB0gXco.png

Website:http://maker.pro/arduino/projects/ho...metal-detector

[Qiaozhi]

This circuit is a simple BFO design. I wouldn't waste your time.
There are many better designs here on the Geotech website.

[Skippy]

It's a fun little project, and technically a bit more interesting than basic BFO's, due to the frequency multiplier. You will learn about some things by building it ... such things as shielding, sensitivity to presence of your hand near the circuit, power supply sensitivity ( there is no regulation of the PP3 battery supply ) , how troublesome 4046 PLL IC's are.
So:
C1, 2 , 4 , 5 are all 100 pF
C6 is 390 pF

[NOriyuki]

Thank you both for your comments!　
Here in Japan we don't have such a forum and this one is very helpful for making metal detectors.

[WM6]

Probably somewhat better picture:

[Skippy]

The frequency mixer is based on a 4011 NAND gate ( pins 11, 12, 13 ) . A better mixer is obtained if this gate is replaced by an XOR gate. There are two ways this could easily be achieved : there is a way of using four NAND gates ( eg. CD4011 ) to create an XOR function; this would be best, as no other changes are needed. Or there are single logic gates, sometimes called 'tiny logic' , in small surface mount packages. These unfortunately normally have a maximum power supply voltage of 6V.
One useful way of improving this circuit would be to regulate the power supply to 6V. This would make it more stable and consistent. The audio amplifier can still be powered directly from 9V, it's the logic and oscillators that are the troublesome parts.
Alternatively, regulate the supply to 9V ( or 8V or 8.5V ) , and use a 12V battery supply ( eg. three lithium rechargeable cells, or eight AA alkaline cells ). There are 8.5V linear regulator IC's, like the L7885, which may be useful.

[WM6]

there is a way of using four NAND gates ( eg. CD4011 ) to create an XOR function; this would be best,
regulate the supply to 9V ( or 8V or 8.5V ) , and use a 12V battery supply ( eg. three lithium rechargeable cells, or eight AA alkaline cells ).
There are 8.5V linear regulator IC's, like the L7885, which may be useful.

[ivconic]

This circuit is a simple BFO design. I wouldn't waste your time.
There are many better designs here on the Geotech website.

NOriyuki listen to George, I agree with him.
Depending on your level of knowledge and skill...though I think you could start with something more advanced and better.

[NOriyuki]

Thanks to all of you knowledgeable folks for your comments and support. I am aware that there are more sophisticated metal detectors out there, but I am still a novice (elderly) myself and have not caught up with understanding the complex circuitry. What I would like to achieve now is a metal detector with a coil about 50 cm in diameter to detect plastic debris with aluminum deposition. the F-75 (Fisherlab) metal detector could not suppress the malfunction due to noise from the electromagnetic motor. (The same is true using frequency shift).
I found that a simple circuit like the handheld metal detector was less susceptible to electrical interference from electromagnetic motors in close proximity. Therefore, I obtained and created the circuit diagram as shown above. However, when I measured the frequencies of IC1 and IC2 in the adjustment, I found that IC1 had a frequency of 12 kHz and IC2 had a frequency of about 700 kHz. The explanation stated that the frequencies of the two ICs must be matched and that PR1 should be adjusted to achieve this matching, but even when PR1 was rotated, the frequencies did not change from around 12 kHz. That is the point where I am stuck now. By the way, VD is using MV209 because MV2105 is not available here. Also, JT is using a 500kHz ceramic resonator instead of a crystal resonator. Is this also the cause of the problem?

If you could give me any other information on good circuits or ways to improve a metal detector that can be used under the above conditions, I would be very grateful.

I apologize that these words are machine translated and may not be clear.

[kt315]

This circuit is a simple BFO design. I wouldn't waste your time.
There are many better designs here on the Geotech website.

my voice is same. you just waste your time. anyway, you got some experience in the electronics but your BFO is a dead horse bitten by the Noth America grizzlies.

死んだ馬

[GeoMax]

Hi KT315,

let him make his own experiences. Soon or later, he will notice that a “dead horse” can not run…

[kt315]

GM, this is Japan... not Lietuva degradanted county without electronics. huge industrial, FIRST place in the world on high tech, THE LEADER.
and just BFO,,, while we wait PI with color display, wonderfully discrimination and much much advanced device Made in Japan.
but... just BFO, schematic taken from global net, i can bring millions the same trash here. but will be a sense? dead horse carcass.

[Skippy]

"Also, JT is using a 500kHz ceramic resonator instead of a crystal resonator."
This is your first problem to solve. There are recommended oscillator circuits for ceramic resonators.
This post ( and others before/after it ) has info on ceramic resonator circuits:

https://www.geotech1.com/forums/foru...699#post413699

Ceramic Resonator Principles - ECS Inc. (ecsxtal.com)

Once you have this sorted out, then work on the variable oscillator. The varicap diode is to fine-tune the frequency. The circuit should oscillate at roughly the correct frequency ( slightly higher ) without it fitted. Get it working without, then try and add back the diode and potentiometer parts.

[Skippy]

"What I would like .. is a metal detector with a coil about 50 cm in diameter to detect plastic debris with aluminum deposition"
This is what is unknown. The deposition may give a weak response, and may be seen as a high frequency target, where 100+ kHz detectors would be a good choice. However, I think your idea about 50cm is unrealistic. 50cm coils are not used much on any detector, and I think on a BFO they would be troublesome. try making a more realistic 25cm - 30cm coil first.

[NOriyuki]

I'm so grateful to everyone who has shared their insights. I'll definitely keep your thoughts in mind as I continue my search for a living horse (a newer technology). Thank you all for your help!

Additional note: Despite Japan's world-class reputation in electronic engineering, I find it intriguing that there appears to be a complete absence of domestic companies producing metal detectors specifically for treasure hunting.