Carl's fluxgate Gradiometer ckt.

[damiafix]

Hi guys,
I'm checking the gradiometer's connections and the integrity of the various IC's.
I've noted that sometime the tension on the DAC, between GND and pin 16, is also 4.5 volts. I think that it's damaged; from the AD557 datasheet I read that the tension on the Vcout should to be max 2.5volts.
What do you think?
About the SCL007, someone could tell me the reference tensions? I wish to check anything!


Cheers, D.

[Krzysztof]

service

Hi.
Pin 16 may be 4.5 V, never.
Check:
1. Transistor Q1 inversely inserted or defective
2. Do you have GND on pin 12 and 13.
3. Short-circuiting of the IC3b.
If you disconnect the pin 14,15,16 can be max 2.5 V.
Check voltage at IC3 pin 1,2,3,6,7.
Vcc2=?
Apply and let us know, the rest later.
Best regards Chris.

[damiafix]

Dear Chris,
many thanks for your reply and for your precious help!

I've removed from the PCB, the IC3-LM393 and the IC4-MC34119, and mesured the tension on PIN 16 of the DAX-AD557; unfortunately when I move a metal object near one of the sensors, the tension have peaks of 4,5volts.

After that I've switched on the gradiometer, and waited several seconds, I've moved a metallic object and placed it near one of the two sensors.

1- I've checked Q1 the transistor 2N3906, with my tester, it seem to be ok. I've changed it with a equivalent, a 2N2222A, but it's the same. So, I've removed it from the PCB and misured the tension on the PIN16 of the DAC, but I've read still a peak of 4,5v; so I've monted again the Q1 on the PCB.

2- Yes, I've GND on the PIN 12 and 13 of the DAC.

3 - I've removed the IC3, nothing of better.

4- Those are the tensions misured on the two IC, with a metallic object placed close one of the two sensors:

DAC-AD557
Pin1-to-Pin8: 4,99v
Pin9: 0v
Pin10:0v
Pin11: 4,99v
Pin12: 0v
Pin13: 0v
Pin14: 2,53v
Pin15: 2,53v
Pin16: 4,12v

IC3-LM393
Pin1: 0,02v
Pin2: 4.55v
Pin3: 4,96v
Pin4: 0v
Pin5: 4,96v
Pin6: 4,12v
Pin7: 4,12v
Pin8: 4,99v

What do you think?

I'm reading the VCO part, described on the FMX1 manual:

The VCO is the only part of the circuit that requires any further
explanation. While there are integrated circuit VCOs available, it is
difficult to locate any that are very low power (<1mA) and readily
available from common sources (i.e., mail-order houses). Thus a simple
but effective VCO was designed around the LM393 dual comparator.
Figure 6 shows a simplified diagram of the VCO. Q1 is inserted into the
feedback path of the DAC output amplifier so that, via the DAC feedback
resistors (about 1.6K total), it performs a voltage-to-current conversion for
driving the integrator capacitor C5. Therefore, the current drive from Q1 is
directly proportional to the DAC output voltage. Interestingly, the true
DAC output voltage is not seen at the output pin (16) but at the feedback
pins (14/15). This signal is brought out to a separate pad on the PC board
(with an adjacent ground pad) so that it can be used as a true analog output.
However, with the addition of the threshold adjustment R6 this voltage is
not low impedance and should be buffered with an op-amp.

so the PIN16, dont' show the real voltage output? Someone can explain me this? I understand who is the good tension that I shold to mesure on PIN16. I'm sorry!

Cheers, Dam.

[Krzysztof]

service

Hi Damiafix.
Whether it was from the beginning of trials?
Check out the real level of the GND pin 9,10,12,13, not on PCB.
Check Whether it is short ommeter pin16 is a plus 5V. Search for tin or short circuit.
Pin16 AD557 is internally equipped with a passive pull-down resistance is 2 kOhm.
Disturbing voltage is 5V for pin1-8. Normally never pin 1-8 Are Not all together at the level of "H".
Remove the AD557 and check out of SCL007. Do you still "H" pin 1-8?
The surest way is to connect only one sensor and shorted pin17-18, it simulates a perfect calibration. Then all outputs must be the level of "L"?
When the SCL responds Normally back install two sensors.
Instead you can free holes in the PCB on the route to the SCL - AD goldpins fit and used to control the LCD through any small mikrocontroler ( PIC, ST, ATtiny, ATmega).
Mediation processor is Necessary, Because there is no LCD control signals, 8 bit input Already.
Good luck Chris.

[damiafix]

HI Chris,
I'm sorry for the delay of my reply, I was away for work, and I'm back yesterday. I'll try again with you suggestions and I'll let you know the results.
Many thanks for your precious help.

Best regards, D.

[Krzysztof]

Hi Damiafix.
Goldpin is free solder holes in PCB circuits Between SCL and AD557.
There you will have all the productions of the SCL in a parallel format D0-D7.
It can be used for future digital Indication on the LCD monitor through any small microprocessor.
Check if you go around 75kHz signal about 5VAC from your FGM3.
Best regards Chris.

[Krzysztof]

Hi Damiafix.
Write what is the current status of your MAG.
What is removed from the PCB. Is FGM-3 gives the signal.
Can you measure them, whether they are of the range of 50 - 100kHz?
Best regards Chris.

[damiafix]

Hi Chris,
I'm back from some test; I've wired the pin 17 and 18 togheter, and connected one sensor to the circuit, far from interferences (I hope), I've removed the AD557 and powered on the gradiometer, waiting 10 second first of the measurements.
Those are the results of mine measurments:

SCL007

1: 4.99v
2: 3.20v
3: 4.99v
4: 4.99v
5: 0v
6: 0v
7: 0v
8: 0v
9: 0v
10: 0v
11: 0v
12: 0v
13: 0v
14: 4.99
15: 2.20v
16: 1.86v
17: 3.72v
18: 3.72v

again....if I connect the output of the sensor to my scope, I can see a square wave, that change the freq when I move it, or put a metal close it.
Unfortunately I don't have a frequency meter, so I don't know precisely the exact frequency.
With only the SCL007 left connected, the PIN2 of it (Sign bit) change level when I put a metal close the sensor and the pin 13 pulse, this pulse get peaks of 4.5 volts.
If I put the AD557 in the socket the PIN 16 change between 0 to peaks of 4,5 volts!

All the best, Dam.

[Krzysztof]

Hi Damiafix.
It is not bad.
Wait till evening.
Vy 73! Chris.

[damiafix]

Hi Damiafix.
It is not bad.
Wait till evening.
Vy 73! Chris.

Hi Chris,
many thanks again, I would to precise, that after the 10 seconds from the power on, if I measure the pin 13 of the SCL007 (with or without the other IC's left connected) it's 0v but when I put a metal close the sensor, the tension reaches peaks of 4,5 - 4,6 volts!

Best regards, Dam.

[Krzysztof]

Hi Damiafix.
PIN 6(LSB) - Pin13(MSB) OK.
After take-off, with installed: 1 pc. FGM and compact PIN17 - PIN18 is the right image after synchronizacjii.
PIN13 with metal can give a sign of excess coverage.
If I put the AD557 in the socket the PIN 16 change between 0 to peaks of 4,5 volts!This is very promising! I do not see short-circuit.
Prepare tests for the moment.
Best regards Chris.

[Krzysztof]

Hi Damiafix.
First proposal:
Since all signals are digital SCL take a little tester. Take 8 pcs LED and 8 resistors around 1kom. All LED cathodes together and connect a short cable to GND.
Connect to each anode resistors.
PCB between SCL and AD is the government of empty holes. He is best if you have, solder goldpins. PCB will not spoil by frequent soldering.
Ends of the resistors soldered on the best strip, corresponding to gauge goldpins. After the turn of the resistors connect PIN6 - PIN13.
The LED lights make a line from the LSB to MSB.
You now have the latest simple LOGIC ANALYZER.
Test1:
Disconnect PIN17/18 ,
Connect 2 pcs FGM,
Move the metal of the FMG,
Connect power to the SLC,
Watch Aalyser.
After synchronisation LEDs should be extinguished. Then, with a small close-metal should be lit starting from the LSB.
Remember it is digital, not analog!
LEDs shine increments starting from the LSB (PIN6).
At this point, tension, or it is silent (H / L).
Drive the level of know the number of diodes LEDs.
Probably the most important is the closest to the MSB.
The closer to the MSB LED lights, the greater the activation of the FMG. Of course, this is a signal difference drive the FMGs.
Set against FGM3 North/Sound should be felt on your analyzer.
Write the results.
Prosperity Chris.

[damiafix]

Wonderful test!
Let me time for to buy the leds! I hope in this afternoon and, I'll look to make the test tomorrow morning!

Many thanks Chris! Prosperity to you!

Dam.

[Krzysztof]

Hi Damiafix.
I think that you have mounted the stand.
We test the AD557 without FGM and SCL .
Test 2a:
Remove the SCL or make connections to AD alone.
Join your logic analyzer to the AD557.
All inputs PIN1 - pin8 connect to GND.
At PIN16 should be around 0V.
Test 2b:
All inputs PIN1 - PIN7 connect to GND.
Pin8 connect the 5V.
On PIN16 should be around 1.25 V. (50% Vmax)
When this is the AD557 is OK!
Best regards Chris.

[Krzysztof]

Hi Damiafix.
Post #3

DAC- AD557
Pin1 do Pin8 : 4,99 v

Why did you have there, 5V.
So, if something wrong with connecting FGM3?
When FGM3 lie on the table that did not matter, because the synchronization resets the results obtained.
Only then any breach of FGM can result.
SIGN Theoretically, the output should change when a metal FGM attack on one or the other.

Please forgive the English translator.
Unknown your level of electronics.
I am writing in general because I know that similar problems had colleagues from Greece.
Best regards Chris.