Falcon MD20

[dom44]

I found with my ferrite rod it was 60 turns to get 300khz i think the gauge was .22 mm i am working on a layout in sprint right now just trying to get the VCO to work right.

[homefire]

Cool. What wire did you use and how many turns about. I have all parts. Need to figure a way to burn a board from that lay file I guess.

[dom44]

my coil head

[dom44]

ic 555

yes it does the 555 is just an oscillator to drive the speaker it replaces the sounder i am currently working on a vco as i think it will improve the sensitivity by altering amplitude as well as frequency of the sound at the moment its basically on or off switched by the final transistor, but as it stands it works just like the commercial unit will pick up a 3mm piece of component wire at 5mm easy the copper ring is the key and its placement in relation to the ferrite rod and the the coil shape, it doubles or triples the sensitivity of the unit.

i have also found the shielding to be important it must be a broken circle if it forms a ring will desensitize the unit as i have found through experimenting the same as a conventional metal detector coil. i am playing with conductive graphite on the end cap to act as a shield.

[homefire]

Tim that board shows a IC. Schematic does not. Is that LM555 and unlabeled pads speaker ?

[dom44]

this circuit works I am still playing with the shielding and some mods it is just as sensitive as the commercial one the copper ring is very important and the coil shape I will post a video and more detail soon.

[Tim]

Hello my neighbor.Your schematic has a few differences to the one posted here. When I re-checked the board here, it is correct. I will put them here so you don't have to search.
This board LAY file is the one here called LAY1.

[Wahyu]

thank Tim, i'm from Indonesia,
this sch please correct me

[homefire]

Start reading on page one of this thread. It's all here.

[karim1980]

Please, I want a pcb+coil+Electronic parts , and everything about the device falcon md20

[Tim]

Great stuff Wahyu! Are you in Indonesia? Phillipines? Malaysia?. Once you fit a 555 IC with R's and cap(s) you should be able to use speaker? Also this should allow for more sensitivity. Did the wiring of the diodes on the pcb need to be changed to match the schematic, as I indicated above?
I have not made this one yet. I bought a MD20 off Ebay- it cost AUD$300 at auction(new, unused). Then last week one sold for $170(bugger!).

I hope you can translate/supply some more information here. Thank you for sharing.

[Wahyu]

my first test diy md20falcon

https://www.youtube.com/watch?v=YBfccvcAecQ

[Tim]

Hi. I think I have found a mistake in the LAY file. Lower middle pot goes direct to .01&100K(RHS),and to cathode of D2. Anode of D2 joins cathode of D1, and .01(LHS). Can anyone confirm this against schematic? Perhaps interested parties with Sprint or other could update the etch? ( I only have viewer).

[ODM]

Yep, assumed they were built as spool from the picture. For use in soft ground with a more durable probe tip (fiberglass or aramide pipe), drawing grooves into the ground, it could sense the sides of that groove while being drawn, like a very shallow plowshare.

With one half of a round pot core, cross section like an E letter, the field is focused on just one side, I would assume making it better for probing downward without pushing the probe into ground. The field might not extend as far compared to a ferrite rod, even a short range detector would probably notice the difference.

[Teleno]

A bobbin like that murata will compress the field to its sides though for probing in sand that might not be bad.

Though I haven't dismanteled this bobbin it appears not to be ferrite shielded, there's ferrite on the front and in the core but not on the sides (you can feel the wires with your fingers).