TL12000

[Asanka Sanjeewa]

Dear my all friends and haylaz0036
In first, sorry for delay.
Do these things if you want the circuit to work properly.
1) Don't use FET transistors. I also put FET and it got too hot. If you put them, you have to change value of the resistors in the TX circuit. BU508ATransistor is the only option. I tried many transistors but only this one gave the best results. At least the BU508D transistor didn't work because it internal diode. Don't forget to put heat zink.Insulation is mandatory [heat sink].

2) Apply variable resistor first for sampling delay. This is because the delay required for iron rejection varies depending on the inductance of the coil. If you adjust the inductance 420uH - 520uH of the coil you can reject iron object at 50k ohm - 67k ohm .Therefore, finding the right value by applying the variable resistor best option first.A permanent resistor can then be applied. (After finding the correct value)
3)As you say, I did not experience excessive battery discharge. I added the voltage to 28 in the battery serial system (18650 Li-ion battery 1800mAH ) and gave 18V through a LM2596 DC-DC converter. It was a more stable supply.

[Asanka Sanjeewa]

Damping Resistor 330 ohm 2 watt
Tx power Transistor is BU508A ( for better results) and put it with heat sink , Do not use FET

[haylaz0036]

Dear Asanka, I don't understand how this distinction works, I rejected iron, it's nice, but at the same time, it rejects gold, copper, silver, everything.

[Detectorist#1]

Dear Asanka and haylaz0036,
Nothing strange in this design. FET transistors like IRF740 are controlled by voltage, bipolar junction transistors are controlled by current. Just see the datasheet of BU508A . Current gain is 30 at low collector's current and appr. 15 at collector current of 2A. With base resistor of 220 oHms and supply voltage of 18V, base current is 18/220=80mA. Max collector's current is 80mA x 30 = 2.4 A theoretically. But with increasing of the collector current, current gain go down and the final current will be less. In the case of FET transistor the situation is totally different. The final current will be (18V x 200us)/400uH =9A ( IRF740 transistor have Rds<1 oHm). As conclusion - in case of using FET - duration of the transmit pulse have to be reduced 5-6 times for the same transmit power and no overheating of the switch transistor.

[haylaz0036]

THIS 508 is very successful, there is no heat, I used IRF. It gets very hot and the depth drops. 200mhz is very successful. It fails when it reaches 400mhz. 1.60cm 20x20 gayat looks good, there is no problem in detection, I just cannot isolate the metals. CD4013. A 100k pot is connected to the 4148 diode next to it. The metal is separated with it. Yes, it isolates. Unfortunately, iron, gold, silver, copper are all isolated, I am looking for a solution.

[Detectorist#1]

Hi haylaz0036,
Give up the TL12000 project. This is the only way your suffering will end. If iron/non-iron discrimination is most important to you, follow the DFBovers project "New project - MPS - Iron discriminating metal detector".

[haylaz0036]

I think it will be deeper than TL12000, it is a really nice device, but I don't want to pay attention to what you say, is it better?

[Asanka Sanjeewa]

Dear haylaz0036 and Detectorist#1
What you say is correct in theory. But I tried many FET and other power transistors. But maximum distance, minimum heating was obtained only from this BU508A Transistor. And I'm sorry for you haylaz. If I were in your country, I would make a PCB kit.
But I think you have turned the reject pot.meter too much. Because there is a very small resistance gap between the separation of iron and the separation of other metals. If you do not adjust this delay controller very carefully, all other metals will be rejected besides iron. This may be due to your lack of experience in building metal detectors. Anyway, I think you will be able to make the felezjoo pi detector easily. It is easy for you because it has digital iron rejection method. You don't need to search correct value rotating variable resistors like this. If your purpose is to reject iron, the felezjoo pi is suitable [ eazy way ] . But pulse induction devices do not provide true metal separation. It actually depends on the conductivity and shape of the metal object.

[haylaz0036]

Dear Asanka, I made felezjoo, it works fine, but it is not as deep as the TL12000. Now I have two TL12000s. One is the normal original, the other one is your modified sound 555, the original one is very nice, the depth is super, yes, this 508 is installed, but your modified IRF830 is installed, maybe that's why the depth is low. Dear Asanka, I wonder if I should wear a headphone with two resistors for discrimination, but what will be the resistors?