Bipolar PI design

[Detectorist#1]

Hi Carl, many of us, ITMD3 readers, are very grateful for your efforts in favor of DIY detectorists to be involved in this exciting hobby!

[Carl-NC]

Thank you. It's a 2-way street, I've learned a whole lot from everybody. ITMD has been a way to put it all together and share it back.

[boilcoil]

...I've recorded ...

Hello Eduardo,
I watched the video, really good design.
I noticed that all IC are mounted on sockets, which is a good choice for hobby electronics.
In the project, you use analog switches, type 4066, which, however, have one feature that may or may not be useful, depending on the specific application.
When a positive voltage is applied to pin nY (1Y, 2Y, 3Y, 4Y) relative to the corresponding pin nZ (1Z, 2Z, 3Z, 4Z) and the drop of voltage in the on state is greater than 0.4V, then current flows to pin nZ from the power supply of the chip (with reverse polarity, this effect is not observed).
You could try directly replacing 4066 with 4016. Of course, the 4016 has more resistance in the on state, but you put serial resistors of 1k in the circuits of the incoming signals, so it doesn't matter much.
IC 4016 is much simpler than 4066, but the aforementioned effect is not observed, i.e. it is completely symmetrical. Replacing 4066 with 4016 may or may not improve detector performance.

Please try this and share in the forum.

[Detectorist#1]

Hi boilcoil,
I just assembled one simple tester for 4016 and 4066 analog switches.
The schematic is attached.
You are right - these switches have problem when voltage between input and output of the switch in ON state is more than 0.4V-0.5V. Only in the datasheets of 4016 and 4066 from TI company have at first look strange information for MAX current via switch. Other companies are silent for this problem. For 4066 max current is 1.3mA and for 4016 max current is 0.5mA according datasheets at 10V supply voltage. The reason for those difference is different resistance in ON state. After your post, I understand why this strange parameter exists in the datasheets for 4016 and 4066 from TEXAS INSTRUMENTS company. Thank you for your post!

[eduardo1979]

Hello Boilcoil. I've tried with 74HCT4066, 74HC4066, CD4066, and CD4016. There's no difference in depth. The only difference I notice is that the Ground Balance drifts very slightly, and I have to readjust the potentiometer. The drift is minimal. I've tried with a Hot Rock.

[boilcoil]

Thank you, Eduardo for the tests done and for sharing them in the forum. Thank you again