The Raptor Project

[Dixix]

I would like to build a IB MD.
But before I try myself to the TGSL or IDX project, I wanted to build the Raptor MD from the book "Inside the metal detector." There, the project is very well explained. Good for teaching purposes.




A step - by - step instructions for building the components can be found on page 117
I am unfortunately only come through step 5.
The Signal on TP1 is correktly:



So my TX circuit works. The frequency 10 kHz (the oscillator with 2 transistors)

the next step (5/6), I have a problem
I have no Signal on TP3 (on oscope)

The only signal which is I still get to TP5:



Can someone please help me? I'm pretty clueless.
Thanks
Dixix

Here the Link of PCB layout:
http://www.geotech1.com/forums/attac...5&d=1354394345

[Qiaozhi]

One important point that you've missed, is that you should have built the circuit in sections, testing each section as you go. From your photo, it looks like you populated the whole board in one hit. At this stage I would suggest removing all the ICs from their sockets, except U1 (the preamp). The signal at TP3 is the output of the preamp, which is amplifying the signal from the coil. If the +5v and -5V supply voltages are OK, then check the RX voltage on the coil.

[Dixix]

you are great!
I have done as you have suggested.
I have at step 7 monitor the signal on TP3 with Oscope:



The next step (the battery check circuit) also works very well.

[Dixix]

And now I've build the sampling circuits.
I've short the 2 pins that connect to the DISC CONTROL pot.

Now I have monitor the both signals:
at TP2 (DISC SAMPLE = yellow)
at TP3 (RX pre-amp = green)



It is right so? Have I understood correctly?
(I have some difficulties to understand the sentence in the book: "...adjust the DISC OFFSET preset until the pulse is positioned centrally over the positive part of the RX signal")

Many thanks for the advice!!

[Qiaozhi]

you are great!
I have done as you have suggested.
I have at step 7 monitor the signal on TP3 with Oscope:

[ATTACH]27025[/ATTACH]

The next step (the battery check circuit) also works very well.

The signal at TP3 should not be a square wave. Try adjusting the coil overlap until you see a sine wave.
It looks like the preamp is being overloaded by the input signal, but your scope appears to be set for 200mV per division. So I don't understand what's going on there.

[Qiaozhi]

And now I've build the sampling circuits.
I've short the 2 pins that connect to the DISC CONTROL pot.

Now I have monitor the both signals:
at TP2 (DISC SAMPLE = yellow)
at TP3 (RX pre-amp = green)

[ATTACH]27026[/ATTACH]

It is right so? Have I understood correctly?
(I have some difficulties to understand the sentence in the book: "...adjust the DISC OFFSET preset until the pulse is positioned centrally over the positive part of the RX signal")

Many thanks for the advice!!

You will need to fix the problem with the preamp first before moving to the next stage.
However, looking at the scope picture, the sample pulse (yellow) is switching between +0.6V and -0.6V. This should be +/-5V. Are you certain the power supplies are working correctly?

[Dixix]

I'm so glad you help me! Thank you!
Okay. I will go back again to TP3.

Perhaps the problem is the self-made coil.
Question: Can I use this little coil (ca.10cm) of the MD COMPADRE?



(I've now got an English-German dictionary specifically for electronic technical terms from the university library)

[bernte_one]

hello dixix

normally the compadrecoil should work
its the same like all 5pin series from older tesoro

the differece between tx and rx coil inductance is in most cases around 0,5mH

i have only started my raptor but not finished
good luck

[mschmahl]

Hello Dixix,
for the sine wave on TP3 it doesn´t matter if it is a tesoro coil or an other. You have to use the right tx-cap. If the inductance of tx is to wrong, than the oszillatorpart of the raptor doesn´t start. I have built the raptor. You can ask me by PM in german.

[Qiaozhi]

I'm so glad you help me! Thank you!
Okay. I will go back again to TP3.

Perhaps the problem is the self-made coil.
Question: Can I use this little coil (ca.10cm) of the MD COMPADRE?

[ATTACH]27031[/ATTACH]

(I've now got an English-German dictionary specifically for electronic technical terms from the university library)

Have you fitted all 20 jumpers into the PCB? If you've missed some out, the preamp may not have any power supplies.

[Dixix]

Thanks for the replies. Thanks also for the helpful hints. I want to once again study the whole chapter ninth.
(and the preparatory previous chapter)
I think I have as much misunderstood. I really want to understand the IB system from scratch.
Also where and what I need to measure.

I was too hasty. I wanted to see results quickly. But as I learn nothing.
First theory then practice!
I'll get back when I'm ready

Thank you again!
Dixix

[Dixix]

Now I would like to continue working on the Raptor project.
(20 wire links is on my board)
I once again point 5 (page 117) are processed.
I have the BC212 and BC548C used for the oscillator (Q1+Q2). I hope that's ok? (BC238 was not going to get)




The frequency is correct: 10.62 kHz.
But the peak to peak amplitude is about 16V. (and not 12V)




I can not explain it to me.
The probe of Oscope is set 10x.

[Dixix]

I have checked the power supply:
TP10 = +9V
TP8 = +5V
TP11 = -8,9V
TP9 = -5V
At U1 following voltages are:
Pin 1 = +48mV
Pin 2 = +48mV
Pin 3 = 0V
Pin 4 = -5V
Pin 5 = +5V
Pin 6 =

Pin 7 = +3,6V
Pin 8 = +2,5V

[Qiaozhi]

Now I would like to continue working on the Raptor project.
(20 wire links is on my board)
I once again point 5 (page 117) are processed.
I have the BC212 and BC548C used for the oscillator (Q1+Q2). I hope that's ok? (BC238 was not going to get)


[ATTACH]27141[/ATTACH]

The frequency is correct: 10.62 kHz.
But the peak to peak amplitude is about 16V. (and not 12V)


[ATTACH]27142[/ATTACH]

I can not explain it to me.
The probe of Oscope is set 10x.

16Vpp is perfectly ok. You can use virtually any general purpose transistors, such as 2N3906 and 2N3904. These will give you about 14.2Vpp. The design will work over a quite a range of values.
However, as mentioned in the book, check and double-check the transistor pinouts before fitting.

[Qiaozhi]

I have checked the power supply:
TP10 = +9V
TP8 = +5V
TP11 = -8,9V
TP9 = -5V
At U1 following voltages are:
Pin 1 = +48mV
Pin 2 = +48mV
Pin 3 = 0V
Pin 4 = -5V
Pin 5 = +5V
Pin 6 =

Pin 7 = +3,6V
Pin 8 = +2,5V

You should recheck the measurements for U1. For example, pin 8 should be +5V (not correct) and pin 4 should be -5V (correct). Some of the others don't look right either.