METAL DETECTOR HELP easytreasure

[JimB]

Interesting chemelec.

What did you use for the coils?
What was the frequency of oscillation?
The circuit would be better defined if you had a decoupling capacitor on the supply line.
It also occurs to me that the circuit may be better with the base decoupled as it is basically a common base type oscillator circuit.

JimB

 

[chemelec]

Interesting chemelec.

What did you use for the coils?
What was the frequency of oscillation?
The circuit would be better defined if you had a decoupling capacitor on the supply line.
It also occurs to me that the circuit may be better with the base decoupled as it is basically a common base type oscillator circuit.

JimB

Yes there was a Bypass Cap on my Supply But I Did not include it in this Schematic as it is on the other part of the Origional Circuit.

The 470pF Caps can also just be 47pF ones, for Less Capacitive Loading.

Actual Tests with "Delivan" Chokes, 10% tollerance ones:

220uH Choke
101 Khz.

100uH Choke
162 Khz.

22uH Choke
283 Khz.

 

[JimB]

Delivan ?

My first thoughts, which were supported by a quick google, were of a mobile catering service, ie Deli Van.

Please tell, what is Delivan?

JimB

 

[chemelec]

Delivan ?

My first thoughts, which were supported by a quick google, were of a mobile catering service, ie Deli Van.

Please tell, what is Delivan?

JimB

Delivan: A Manufacturer of Small Choke coils.
Not sure if they are still in business, but I have Hundreds of them in Many Values.

 

[alec_t]

Nice one, chemelec.
I agree Spice isn't perfect. Thought you might like to know though that it predicts ~155kHz (load dependent) oscillation frequency for a 100uH coil in your circuit. Not far off reality .

 

[RECEIVER7]

can u tell me in grater detail how i would use the frequency counter on this be as i no nothing my counter is is a dmm good luck with prototyping it

 

[chemelec]

Nice one, chemelec.
I agree Spice isn't perfect. Thought you might like to know though that it predicts ~155kHz (load dependent) oscillation frequency for a 100uH coil in your circuit. Not far off reality .

Spice uses PERFECT PARTS.
The Real Coils are NOT Perfect.
These one are + / - 10 % of value.

Capacitors are Also NOT Perfect.
Also + / - 10% or sometimes even 20%.

 

[chemelec]

The Coils I Used for my TESTS.

can u tell me in grater detail how i would use the frequency counter on this be as i no nothing my counter is is a dmm good luck with prototyping it

What is the frequency range of your DMM Counter?

What are you using for Coils?
Normally for a BFO Detector, you would use one Factory made Small Coil, than Wind a Seach Coil with the Same Inductance as the Factory Coil.

So an "Inductance Meter" would be More Useful than the Frequency Counter.

 

[chemelec]

Sorry for this Spelling error, it is delevan for the Coils I use. (Not delivan)
http://www.delevan.com/web/

 

[tvtech]

Thanks Gary

Good you are posting here again. You know stuff about Metal Detectors and related Electronics that I know squat about
I am all ears and learning

All the best,
tvtech

 

[ccurtis]

LTspice thinks it will (assuming ~ 100uH coils), but it would be interesting if you could confirm with a breadboarded version.
LTspice agrees. Oscillation does occur in the sim, but amplitude is only ~0.7V.

But, place a capacitance across the coils and the amplitude will rise greatly at the resonant frequency (assuming the transistors can operate at that frequency).

If I was to get a hankering to build a metal detector, I would consider this neat device to build it around: https://www.ti.com/lit/ds/snoscy1/snoscy1.pdf

 

[chemelec]

https://www.ti.com/lit/ds/snoscy1/snoscy1.pdf

Looking at the Data Sheet, I believe this device is Only good for VERY SHORT RANGE of Detection.
It looks like it is specifically made for detection of STAINLESS STEEL, Which is Not Detected by most metal detectors.

 

[alec_t]

Looking at the Data Sheet, I believe this device is Only good for VERY SHORT RANGE of Detection

That's what I think, too. Since the IC both drives the coil and uses the coil as a sensor I don't see any obvious way of boosting the coil current to increase the detection range. Pity.

 

[ccurtis]

https://www.ti.com/lit/ds/snoscy1/snoscy1.pdf
Looking at the Data Sheet, I believe this device is Only good for VERY SHORT RANGE of Detection.

At the TI website:

Q1: What is the maximum target sensing distance for the LDC1000?
Answer: The rule of thumb is

• for high sensing resolution, a target with a size comparable to the size of the coil can be sensed at a distance of up to half of the coil diameter
• for presence detection , a target with a size comparable to the size of the coil can be sensed at a distance of up to the coil diameter

https://e2e.ti.com/support/data_converters/inductive-sensing/f/938/t/295036.aspx#Q1