Tesoro Coil and TGSL

[sled]

hi,

I've just finished the TGSL (ivconic's version). Since I had an original Tesoro Coil I thought I could use that one. Problem is, that it's a newer coil with the four pin connector. TX is 0.95mH and 4.3 Ohm and RX is 15.8mH and 63ohm.

Therefore I changed the TX oscillator (replaced bias resistors and caps, basically I used the values from the Cibola detector). The TX signal is a clean sine wave at 14.45kHz with about 17Vpp amplitude.

The RX seems not to work properly, I calculated that 6.1nF in parallel to the 15.8mH coil should yield a resonance frequency of 16.2kHz.

The problem I have is that the detection depth is only about 5-10cm even for large objects like a full reel of solder wire.

When I measure the RX signal right before the LF353 I get about 8-9Vpp @ 14.5kHz with respect to battery ground.

Any ideas what could cause the problem? :S

The coils work fine on my original cibola.

Thanks

[dfbowers]

To begin with, your Rx signal does not sound right at all. Your Rx signal should be in the mV range or the LF353 will be swamped. I think I played with this coil at one time and got it to work.

[Silver Dollar]

I had a similar problem with my home built TGSL and Coil. I had to remove the 5.1K/4.7K on the input opamp
and ground the other (basically using ti as single ended) to get it to work...

[sled]

To begin with, your Rx signal does not sound right at all. Your Rx signal should be in the mV range or the LF353 will be swamped. I think I played with this coil at one time and got it to work.

Hm... fun fact is that the 9Vpp across the RX coil seems to be there regardless of the LF353, I get the 9Vpp also when I remove the RX coil completely from the circuit and hook it directly to my scope The 9Vpp is measured with the scope grounded to the ground of the voltage regulator/battery.

When I connect one lead of the RX coil as ground to my scope I get a sine wave in the mV range though... Any idea? :S

[Koala]

Has the scope probe got knocked onto X10

[sled]

Has the scope probe got knocked onto X10

I use a x10 probe and I set the scope to x10, the voltage seems to be correct, I measure 8V on the regulator.

It's strange that I get 9Vpp on the RX coil with a 17Vpp signal on the TX coil... I measured the resistance between the connector pins and everything seems to be ok, there is no short circuit between the coils...

[sled]

I built the TX oscillator on a breadboard for testing - it's the same problem. Turns out the whole RX signal is modulated on to a HUGE 50Hz signal, I think that's causing the 9Vpp amplitude. The 50 Hz is all over the place even when powering from battery. Seems like I have to test it outside.

Touching the coil shell couples in even more 50Hz noise since the plastic used is conductive.

PS: Don't use energy saving lamps near your scope probes

[Daren]

@Silver Dollar: can you elaborate what change was need exactly and why?

[Silver Dollar]

Well I had low detection depth and figured the coil was not balanced so why is the input?
So I tried making it a single ended input and got greater depth.

[Daren]

Thanks,

[Silver Dollar]

While this improved my TGSL I tried it one my Bandito and lost depth!
There's funny things going on in these circuits. Increasing the TX amplitude
didn't work on the Bandito either it lost depth!