I do hunting metal detector

[aojieage]

The metal detectors, I do a few days ago, I started using universal circuit board test (Figure 1), but my initial tests are successful, the PCB production (Figure 2).But I is still very limited detection range, 25mm diameter, 2mm thick stainless steel coin in the air only to explore 10cm Please help analyze what is the reason?Me around the spider line compared Tesla around, too ugly, the effect is not as good as the spider coil.My emission current 10-20mA, frequency 100-200Hz.

[Qiaozhi]

The metal detectors, I do a few days ago, I started using universal circuit board test (Figure 1), but my initial tests are successful, the PCB production (Figure 2).But I is still very limited detection range, 25mm diameter, 2mm thick stainless steel coin in the air only to explore 10cm Please help analyze what is the reason?Me around the spider line compared Tesla around, too ugly, the effect is not as good as the spider coil.My emission current 10-20mA, frequency 100-200Hz.

It is a bit difficult to help you "analyze the reason", when you haven't even told us which design you're building.
Is this your own design? Where is the schematic?

[aojieage]

Sorry my English is not good, had to use GOOGLE translation.
The first is the schematic, due to my lack of components, the circuit made changes in Figure 2. The operating current of the optocoupler I use 1mA, the beginning is 2mA, burned out a few results optocoupler.

[aojieage]

Has been good!I according to the original design.Of course, it is not enough probing depth.In the future, I want to learn better circuit.：D

[Davor]

I'm not sure optocouplers are a good solution for replacing analogue switches?!

[aojieage]

Is not a good method! This is where I buy not to fet circumstances, shall not have to do. After a period of time, and I bought the field effect tube, has changed, it is working well.