TESORO GOLDEN SABRE

[kt315]

Qi
we use PRF202 here https://www.lemona.lt/?page=item&i_id=38146

[Mr.Jaick]

Hello everybody
i've just sat up my TGSL with 28cm coil
TX: 14.705 Hz and RX: 14.144 Hz
it's fully functional but i think i have some little problem
(1) it doesn't detect above 50 or 60 cm even with a big steel wrench or 1kg of other metals.
(2) it has more depth when i advance the GB pot clockwise more than it needs to reject ferrite.
sample coin(nickel ,copper , zinc or aluminium alloy)
GB set low(less than mid range) = 25cm
GB set high(a bit more than mid range) = 35cm
i'm just worrying about silver rejection...
it doesn't detect copper btw but it doesn't matter to me , just in case to know.
(3) when i switch to disc mode it works perfectly but when i observe the gate of TR4(disc channel) with oscilloscope ,
the waveform disappears after mid range of disc pot(100k)
unfortunately i don't have silver and gold at the time to test if they would get reject when waveform disappears or not...
thank you guys in advance if anyone would help

this is the waveform on gate of TR4:

[waltr]

The TR4 gate waveform looks good at min. However, the 30% & 40% doesn't seem correct.
Compare to the TGSL 101.pdf.

Then re-check ALL components from C9, R19, through to input of U102.
C9 and C10 are fairly critical caps so ensure you use good quality 100pF caps here.

I also assume you used non-counterfeit chips.

[Mr.Jaick]

The TR4 gate waveform looks good at min. However, the 30% & 40% doesn't seem correct.
Compare to the TGSL 101.pdf.

Then re-check ALL components from C9, R19, through to input of U102.
C9 and C10 are fairly critical caps so ensure you use good quality 100pF caps here.

I also assume you used non-counterfeit chips.

thanks sir i'll check again
after 30% it narrows down again while advancing disc pot, that's the reason for 40% waveform
i've used multilayer ceramic caps for C9 and C10 , should i change it to polyester or MKT type?
and i don't know if it's a genuine chip , perhaps chinese or tiwanian ones
i rarely can find genuine chips around

[waltr]

thanks sir i'll check again
after 30% it narrows down again while advancing disc pot, that's the reason for 40% waveform
i've used multilayer ceramic caps for C9 and C10 , should i change it to polyester or MKT type?
and i don't know if it's a genuine chip , perhaps chinese or tiwanian ones
i rarely can find genuine chips around

It is an odd behavior. That why you need to re-check all components. Also recheck the Disc Pot wiring and the pot itself.

I used polyester caps for C9 & C10. So worth trying other caps.

[Nandor]

Hi Mr Jaick.

You have odd waveforms because the Tx voltage is to high for the phase shifter opamps. Listen you have +8 and -6.5~ now thats 14.5 volts powersupply voltage for IC's now you have a Tx that makes 15-16Voltpp and these op maps and comparators arent rail to rail. In order to clear the square waves you have to use for Disc and Geb 14volts at Tx thats enough, and change the Geb 100k resistor with the 15pF capacitor to 47k with 15pF. This way you wont have to much noise in the square waves and Geb signal wont be that distorted triangular it will be a rounded square wave. Oscillator at higher voltages will get distorted sinewave with much noise, use Ivconic's mod and change the 47k resistor at Oscillator to a 100k trimmer and you can make a clear sinewave with that.

[Nandor]

Basically the Disc phase shifter op amp has saturation on the input!

[Mr.Jaick]

Hi Mr Jaick.

You have odd waveforms because the Tx voltage is to high for the phase shifter opamps. Listen you have +8 and -6.5~ now thats 14.5 volts powersupply voltage for IC's now you have a Tx that makes 15-16Voltpp and these op maps and comparators arent rail to rail. In order to clear the square waves you have to use for Disc and Geb 14volts at Tx thats enough, and change the Geb 100k resistor with the 15pF capacitor to 47k with 15pF. This way you wont have to much noise in the square waves and Geb signal wont be that distorted triangular it will be a rounded square wave. Oscillator at higher voltages will get distorted sinewave with much noise, use Ivconic's mod and change the 47k resistor at Oscillator to a 100k trimmer and you can make a clear sinewave with that.

hello Nandor
i think you're right , it make sense
my negative rail is -4.8V and positive +8.15V
first i removed all the 100nF bypass caps from supply rails near each IC(i add them on pcb for noise improvement) except of original schematic caps
now the circuit is exactly the original one
it didn't solve the problem.
second
i changed the R3(base of TX transistor) to 100k trimmer pot and result is cleaner wave form
but it didn't solve the problem again.
third
i changed the R23(output of GB channel 100k ) to 47k
still the same problem for the DISC
and a new one , now it can't reject ferrite (it could't before the last change )
so here is the question how to decrease the TX amplitude without distortion?
now we have a disappointed guy who has spent about 4 months and lot of money on this project to make it work, and nothing
btw i've used 22k instead of 24k for R21(LM393 pin 1)

TX signal:

TX vs RX on output of U1, each block is 53 degrees of phase shift(so it's 20 now)

tx vs middle pin of disc pot, disc pot at min

tx vs middle pin of disc pot, disc pot at mid range

tx vs middle pin of disc pot, disc pot at max


something is absolutely wrong

[Mr.Jaick]

Basically the Disc phase shifter op amp has saturation on the input!

yes and i'm wondering how other guys have made this circuit with 16V tx and no problem, it's very strange

[waltr]

First, the Scope Voltage scale and Time base are Unkown so I can not give much on what you show us.
Also is the scope AC or DC coupled?
Where on the scope is the ZERO Volt level for each trace?

The TX_signal.jpg seems too clean and is NOT the same waveform that is in the Tx_RX_lf353out.jpg.
The TX signal in the second jpg looks like what I expect, with a slight kink near the peaks.

Are you Sure U101 & U102 have both +8 and -5V (-6.2)??

What does the signal going into U102, pin 2 look like? This is a Comparator, When pin 2 Voltage is higher than ground out is high. When lower than ground, output low.
Since the output is HIGH when the Disc pot is turned past middle indicates that the signal on pin 2, AC wave, is completely above ground. This signal should be going positive and negative. This can happen if U101 does not have -5(6.2)V.

[Mr.Jaick]

First, the Scope Voltage scale and Time base are Unkown so I can not give much on what you show us.
Also is the scope AC or DC coupled?
Where on the scope is the ZERO Volt level for each trace?

The TX_signal.jpg seems too clean and is NOT the same waveform that is in the Tx_RX_lf353out.jpg.
The TX signal in the second jpg looks like what I expect, with a slight kink near the peaks.

Are you Sure U101 & U102 have both +8 and -5V (-6.2)??

What does the signal going into U102, pin 2 look like? This is a Comparator, When pin 2 Voltage is higher than ground out is high. When lower than ground, output low.
Since the output is HIGH when the Disc pot is turned past middle indicates that the signal on pin 2, AC wave, is completely above ground. This signal should be going positive and negative. This can happen if U101 does not have -5(6.2)V.

scope time base is 10us per div and voltage is obvious when the tx is large it's 2V/div and when it's smaller it's 5V/div
both DC coupled , trigger source is vertical(VERT)
zero reference for first and second pic is at the X=zero (middle screenl)
for third pic: middle of bottom section and for forth is middle of top section of the screen
the last one is lower than middle screen if i remember it right

that test point on middle pin of the disc pot goes higher in DC and AC waveform dies when i turn it clockwise

TX waveform is clean because of that 100k trimmer, it's not a problem , it changes with that trimmer pot
unfortunately i could't capture the signal on pin 2 of U102 cuz my tx circuit runs unstable perhaps for dirtiness or bad solder joint,
since the pcb is a double sided board, it's so sensitive to desolder components, and that 100k trimmer legs.... but i see the signal before and after those 100pf caps ,
, before caps obviously is tx but after caps was a very low amplitude distorted signal !!! is that normal?

i think my negative rail is a bit low , i don't know why?
it's about -4.8

[kt315]

8 - 0,6 - 0,6 - 1 - 1 = -4.8

0,6V on a diode
1V on C-E of a transistor
why you must see more voltage bit high??

[waltr]

This is a Comparator, When pin 2 Voltage is higher than ground out is high. When lower than ground, output low.

I got this backwards. The Disc pot goes into the Negative comparator input so output high when input low.

Thanks for details on scope pictures.
The signal at the wiper of the Disc pot is moving up as you turn the pot. This is Not correct and why the comparator output goes to a solid high level.
What should happen is the signal should become more and more delayed as you turn the pot.

Did you CHECK the Voltages on the opamp and comparator? -4.8 is lower than typical but should work.
Re-check the Disc pot connections and component values. Check all soldering and since you have a hand made double sided PCB ensure connection are made TOP & BOTTOM where needed.

[Nandor]

Mr Jaick the phase shift between your Tx and Rx does not seem to be 20deg, there is obviously much less than that maybe 10-15 after seeing the picture you posted.

About the negative voltage, try Schotky diodes those have less on resistance and pair those transistors to have equal hFE and also low ESR electric capacitor is a must! The best I have made was around -6.7volts.

Waltr has some really good points also!

[Nandor]

You can also try to use ICL7660 to make negative voltage for the circuit. You need less components and it makes -7.48volts loaded, works splendid!

Do not forget that you have very asymmetrical voltages for the IC's that means that the negative peaks of the signals get clipped. I really believe that this is your problem.

regards