Falcon MD20

[homefire]

Does anyone have any more Info on the Falcon?

Looking for some values here.

Thank You!

[homefire]

OK! it nothing more then a Modified Colpit Osc but how is it doing the detection?

Were in the circuit is it pulling off the freq offset?

[Vortxrex]

Does anyone have any more Info on the Falcon?



Thank You!

Several years ago I went to a GPAA Gold Show in Salem Oregon. I brought along a small (corn kernel) sized gold nugget & a chunk of Ultramafic rock (which is typical of the bedrock here where you find nuggets) I tested the Falcon & you had to be practically touching the nugget to get a response

What I wanted was something I could use in my highbanking operations to scan along the bedrock & working face. I did not think it would work well.


It should be easy enough to figure out the values of the potentiometers, just by trying "obvious" values & tracing the signal, but don't expect it to work any better than an old Studfinder

[Altra]

It's not a BFO or frequency shift detector. The colpits osc is set so that any non ferrous metal close to the inductor causes a change (loading) in amplitude. The buffer amp(2N2222) and 1N34 diodes form an AM demodulator or Rectifier for the sine wave. The change in DC voltage is used to set off the buzzer. The only difference between this and the average stud finder. Is that some of the DC voltage is fed back to the osc to maintain the bias voltage on the base of osc transistor. "Automatic Ground Balance"

Google "Loaded Loop Detector" they were widely used to sense cars at traffic lights.

I have the original unit and will measure the pots tommorow and post.

[Tepco]

In old days, this configuration is called "ALL" or Amplitude Locked Loop. Rectifier and feedback will maintain constant oscillator amplitude at some point, loading the LC tank will change that control signal and this is detected as a target response. Probably worst way to detect metal. Very long time ago, similar circuits, but in GHz range is used for motion detectors in alarm systems, but due to RF interference, abandoned whit mobile phone introduction. Anyway, don't spend too much time on this one.

[DOOLEY]

hello all , just been reading this thread ,
the picture of the insides shows an 8 pin chip labled u1 ,
but neither schematic posted shows u1 on it ,
what is it ? why is it now shown ?

or am i been silly ?

[homefire]

hello all , just been reading this thread ,
the picture of the insides shows an 8 pin chip labled u1 ,
but neither schematic posted shows u1 on it ,
what is it ? why is it now shown ?

or am i been silly ?

If you read the whole thread, you will see that sense the schematic was made up, they upgraded the audio section.

Probably a LM386!

[DOOLEY]

ah , i see , a 386 , but then everyone will know when youve struck gold !

travel in pairs , carry a 45

[Altra]

Here are the values for the pots and trimmers. This is for the MD 8, current model is MD 20. The probe is a 3/8" ferrite core probably 20 to 40 turns of AWG 32? These must be good for something, I believe mine is from the 1980's

[homefire]

WoW! Thank You Sir!

[nelson]

Here is a good video that shows how it works.

http://www.youtube.com/watch?v=OFNbPbAdvGE

Regards

Nelson

You cannot watch a film on their website -> http://www.falconmetaldetectors.com/
but you can buy the T shirt ... and a cap!
Looks like they have a lot of distributors around the world for what is essentially a very simple design.

[6666]

I recently found this good video on MD20, may try and make it, (well add it to the list)
http://www.youtube.com/watch?v=rRiSZ_2AyTI

[Ism]

If anybody has developed a PCB layout for the schematic that was made available in this thread, would you please post it.
I am gathering components to build this project and have never successfully used a PCB layout design program.

[Constantin]

If anybody has developed a PCB layout for the schematic that was made available in this thread, would you please post it.
I am gathering components to build this project and have never successfully used a PCB layout design program.

Just an idea without silent switch.

[Ism]

Thank you, I have been trying with DipTrace but my board looks like crap compared to yours.