TL12000

[Asanka Sanjeewa]

Hi Asanka,
This video and the explanations for "min depth range" are not serious. All tests with waving of the target - not of the coil and in air - not in the ground are NOT serious! According this video, we see the next toy - not real useful MD. Please make video with real tests.

Hi Detectorist#1

Sorry, I mentioned in the video that the tests are done with the minimum sensitivity range [ minimum deep range- not mine deep range] of the device.It was a mistake to shorten the words, sorry

[Asanka Sanjeewa]

Dear Asanka, I watched the video. It is really nice. The iron insulation is nice. The depth is low but it works at minimum. I want to try it. I am preparing the card and materials. Will there be any change before printing the pcb? Should I print the pcb in this condition? I would be happy if you give me the pcb.

Dear haylaz0036,
The lack of distance is seen because the sensitivity of the device has been reduced and the video has been reduced. Because when the distance of the device is increased, the person can be seen. They don't want to show their faces in the video.There is no change in the device layout of the pcb, it is the same as what I sent earlier.However, it is more important to follow Geo Max's instructions if you try to make device.

[Detectorist#1]

Hi Asanka,

In your schematic, you have not "sensitivity" pot. It is interesting how you set "minimum sensitivity range". The pots: TRESHOLD, VOLUME, FREQUENCY and DELAY switch NOT regulate the sensitivity direct.
Only setting of TRESHOLD pot (10 turns pot) have possibility to influence on sensitivity but how far from "sound ON point" this pot is - too unclear setting. And no sense to use MD in "minimum sensitivity". Usually we want to use MD in "max sensitivity" mode if the conditions allows this.

[Asanka Sanjeewa]

Hi Haylaz0036,

I would modify the front-end-receiver and use a NE5534 op-amp. Because this is easier to get compare to a LM709 and probably the better choice. I also would remove the connection at the 555 timer Pin 4. See post #121 for sure. If you do the modifications, the PCB needs some redesign.

Hi GeoMax
Maybe we can use a mosfet that voltages around 380 and a LM 318 with no oscillating noise? [ for metal-silence on the coil ]

[Asanka Sanjeewa]

Hi asanka
What do they find?
Gold items or Gold nugget
can i use this detector for find nuggets ?

Hi Tanu
Maybe you can, try it

[GeoMax]

Hi GeoMax
Maybe we can use a mosfet that voltages around 380 and a LM 318 with no oscillating noise? [ for metal-silence on the coil ]

Hi Asanka,

yes, you can also use an LM318. But that is a very old IC design and the Texas Instruments website recommends using a newer op-amp. I would still prefer an NE5534 op-amp because it is low noise, cheap and easy to get. Eric Foster and many other designers have used this op-amp in their detectors, so it is a proven front-end op-amp for metal detectors. The BU508A can also be easily replaced with an IRF740 or IRF840 MOSFET. They are also cheap and widely available.

[Detectorist#1]

Hi Asanka,

As GeoMax said, LM318 is very old Op Amp. Now days, for the first stage of the simple (not bipolar Tx MD) DIY designs, the best OpAmp is OPA1611AID. This OpAmp haves 3 times lower voltage noise than NE5534 and no needs for nulling parts up to voltage gain of 1000. For Tx NMOS transistors - IRF740 and IRF840 are old design. Now they have improved versions with two times reduced output capacitance (Cds) and many times reduced Drain to Gate capacitance. The names are IRF740A and IRF840A. They are better suitable for PI MD with improved minimal delay ( good for looking for small nuggets).

[GeoMax]

Hi Asanka,

As GeoMax said, LM318 is very old Op Amp. Now days, for the first stage of the simple (not bipolar Tx MD) DIY designs, the best OpAmp is OPA1611AID. This OpAmp haves 3 times lower voltage noise than NE5534 and no needs for nulling parts up to voltage gain of 1000. For Tx NMOS transistors - IRF740 and IRF840 are old design. Now they have improved versions with two times reduced output capacitance (Cds) and many times reduced Drain to Gate capacitance. The names are IRF740A and IRF840A. They are better suitable for PI MD with improved minimal delay ( good for looking for small nuggets).

Hi Detectorist#1,

I suggested the NE5534 because it is cheap, low noise, widely available and is a good choice for DIY projects. For commercial projects, I agree that the OPA1611 is definitely a better choice than the NE5534. Another disadvantage of the OPA1611 is that it also costs 5 to 10 times more than a NE5534 and is not available in DIP8 version. You still need a SO-8/DIP8 adapter socket.

[Detectorist#1]

Hi GeoMax,

For commercial projects the price of every piece is important (the profit is on the first place). For one piece of MD, like DIY projects, the performance is more important than adding of 5USD. This is my opinion.

[Detectorist#1]

The manufacturers for NE5534 in DIP8:
ON semi - not manufactured in DIP8 now
TI_ DIP8 not recommended for new designs from Nov 2014

.... good old days.....

[Altra]

The manufacturers for NE5534 in DIP8:
ON semi - not manufactured in DIP8 now
TI_ DIP8 not recommended for new designs from Nov 2014

.... good old days.....

You can buy NE5534s made by TI in 8 pin dip. Direct from TI $0.90 for quantities of 1 to 100. Guaranteed original. I am sure Farnell, Digikey and mouser have the same part.

[Detectorist#1]

Hi Altra,

Situation today:
Mouser: NE5534P - 3364pcs, NE5534AP - 6918pcs
Digikey: NE5534P- 0 , NE5534AP -0 non stocked more
Farnell: NE5534P - 53pcs , NE5534AP - 111pcs - both will be supplied until exosting

[Asanka Sanjeewa]

Hi Asanka,

yes, you can also use an LM318. But that is a very old IC design and the Texas Instruments website recommends using a newer op-amp. I would still prefer an NE5534 op-amp because it is low noise, cheap and easy to get. Eric Foster and many other designers have used this op-amp in their detectors, so it is a proven front-end op-amp for metal detectors. The BU508A can also be easily replaced with an IRF740 or IRF840 MOSFET. They are also cheap and widely available.

Thank you very much for the advice.

[Asanka Sanjeewa]

[QUOTE=Detectorist#1;n432473]Hi Asanka,

As GeoMax said, LM318 is very old Op Amp. Now days, for the first stage of the simple (not bipolar Tx MD) DIY designs, the best OpAmp is OPA1611AID. This OpAmp haves 3 times lower voltage noise than NE5534 and no needs for nulling parts up to voltage gain of 1000. For Tx NMOS transistors - IRF740 and IRF840 are old design. Now they have improved versions with two times reduced output capacitance (Cds) and many times reduced Drain to Gate capacitance. The names are IRF740A and IRF840A. They are better suitable for PI MD with improved minimal delay ( good for looking for small nuggets).[/QUOT
Thank you very much for the advice.

[Asanka Sanjeewa]

Hi Asanka,

what is the delay when discrimination time is on / off in your TL12000?

I try to keep the total sample delay between 20us - 75uS. But in discriminating mode it remembers like 21us. But I don't remember exactly. However, I got the best results at 50.5k ohm, which adjusts the sample delay.But the original designers of the instrument say that the best point for gold is 64.4k ohm. But I didn't get good results at that value.