Standalone Differential Front-end

[KingJL]

I do not recommend building this board as presented above. Stage 2 (IC2) oscillates! I need to breadboard this to investigate, but I believe this is caused by a too low source impedance for stage 2. I believe that adding a 2.2K between pin 6 of IC1 and pin 2 of IC2 and another 2.2k between pin 3 of IC2 and GND will cure this problem.

Ok I have made the changes to the schematic and board layout. I decided to go ahead and etch a board to make the testing easier and to eliminate any circuit instabilities introduced by the breadboard kludge that I created previously. Here is a picture of the board before drilling. I also included the updated schematic, board, and PDF board masks into a new zip for version 2.

[WM6]

Good work, thank you. What mean your comments in schematic "(match HH2 R12)" next to R2 resistor?

[KingJL]

Good work, thank you. What mean your comments in schematic "(match HH2 R12)" next to R2 resistor?

I look at the HH2 design as a starting point. Some things I change (see my HH2 build thread). In his case, I changed R12 of the HH2 from a 1 K to a 2K2. I did this to lower the lower the current during the flyback and the resultant effect on the decay whilst the flyback is above the diode threshold.

If your HH2 R12 is 1K, then R2 of the daughter board needs to be 1K.

[jlsilicon]

Is there Test results as a working Metal Detector ?
- Coin Size , Range from Coil, etc tests ?