Electronic-Nulled Loops

[moodz]

Here is my entry for the nulled loops competition. It uses the ARMD project core and balances the loop via two possible methods. ( internal to the DSP ) or external.
Note in external mode the RX coil "sees" the correction signal !!

The balancing is very simple in reality. We already calculate the signal magnitude and we know the NCO phase and amplitude so its a matter of a null feedback loop.

[Altra]

I built this little circuit to test how well it could null a coil. The next step is to replace the X and R trimmers with digital pots, using a processor to auto null. In the video the tx is running about 14kHz at 16vpp. The pre-amp out can be nulled from about 500mvpp down to 20mvpp.

The circuit is a modified version of the Treasure Mate found here

https://www.geotech1.com/forums/forum/technology/schematics/430924-treasure-mate-pinpointer

https://www.youtube.com/watch?v=a8NI_632VIA