Sniffer XR-71 help

[Jafar]

An unfortunate reality with the old White's detectors is that the rotary-slide switches (used for mode selection) eventually go bad. There is no replacement.

Hi Carl, I need your help.

I've built the Sniffer XR-71 device, but I'm struggling with some issues and could really use your support.

One problem is that no signal appears on the oscilloscope under normal conditions—unless I touch pin 7 of the NE555 directly with my hand. When I do, a signal appears, but as soon as I let go, the signal disappears and the circuit stops working.

I'm also having trouble with the potentiometers. When I observe the signal on the oscilloscope, only the TRESH potentiometer seems to work—it adjusts the frequency between roughly 23 to 30 kHz. The other potentiometers don’t seem to have any effect. For example, the GAIN potentiometer doesn’t mute the sound, and the speaker stays on constantly.

Also, since I didn’t have an LM555, I replaced it with an NE555.
And because I didn’t have a UA556 either, I used another NE556 instead.

Please let me know what each of the pins labeled A1 and P1 to P9 are for.
If you’d like, I can send you photos of any part of the circuit or check it with the oscilloscope.

I’ll also send you the schematic and PCB layout.

[Jafar]

359704040-sniffer-xr-71-kit-manual-instruction.pdf
Esquema_Pulse_delta[1].pdf
Lista_de_componentes[1].pdf
NEW_SINGLE_FACE_PULSE_DELTA_010410[1].pdf
Posi.pdf

[Carl-NC]

I've moved you posts to a new thread. I don't have any experience with the Sniffer circuit, maybe someone else can respond.

[Carl-NC]

I took a quick look, I assume the "P" numbers are test points.
555 timers come in both bipolar and CMOS technology. Sometimes it is critical that you get the right one.

[Jafar]

I took a quick look, I assume the "P" numbers are test points.
555 timers come in both bipolar and CMOS technology. Sometimes it is critical that you get the right one.

"Thank you, Carl. I know you're amazing when it comes to metal detectors, and I’m sure this is just a warm-up for you. I’d really appreciate it if you could guide me further, and I’d also love to get help from others who’ve worked in this field so I can get my device up and running."

[kt315]

i am thinking you have to look on all banch of photos in a folder turkish_PCB in the Archive, i see you have not wires on your pcb. lost.

you do (try to do) turkish layout of shiff sniff. much people got good result, but also much people got nothing.

[Jafar]

i am thinking you have to look on all banch of photos in a folder turkish_PCB in the Archive, i see you have not wires on your pcb. lost.

you do (try to do) turkish layout of shiff sniff. much people got good result, but also much people got nothing.

I couldn’t find the archive folder you mentioned. If you have the link, I’d appreciate it if you could share it.

I replaced two LM555 ICs (used in an astable circuit) with NE555s because I didn’t have the original ones. Also, I substituted the UA556 IC (where the first section, D1A, is astable and the second section, D1B, is monostable according to the schematic) with an NE556. Can you help me rebuild the circuit using the replacement ICs I mentioned, based on whether each part is astable or monostable?

Also, in the UA556, pins 3 and 11—which are both control voltage pins—are not connected to _E via a capacitor. What’s the reason for that?

warm regards

[GeoMax]

Hi Jafar,

it is here....

[kt315]

Also, in the UA556, pins 3 and 11—which are both control voltage pins—are not connected to _E via a capacitor. What’s the reason for that?

never did think about this ))) i see you want to overload your mind by bare info or what? ask you - do not fantazy without a cause. turn out.
here are just hobbists, no PHD Professor from Preston University, USA, cathedra ELECTRONICS. or you want do from zero point?
so i give you attach

[Carl-NC]

I replaced two LM555 ICs (used in an astable circuit) with NE555s because I didn’t have the original ones. Also, I substituted the UA556 IC (where the first section, D1A, is astable and the second section, D1B, is monostable according to the schematic) with an NE556. Can you help me rebuild the circuit using the replacement ICs I mentioned, based on whether each part is astable or monostable?

Always start at the beginning, Make sure all power supplies are reasonably correct, nothing else will work without that.

Next task is to get D1a running. PR1 should vary the frequency but I don't know what the frequency range is on this project. When you have D1a running, then I assume D1b adjusts the pulse width via the 20k pot. Again, I don't know the proper range. All this should drive Q1 with a pulse train. This has to work correctly before moving on.

Then you will need to test the other pulses at test points P2, P3 to make sure they are working. Then start looking at signals down the analog path; P1, Tr6, Tr7, etc. All of this requires an oscope.

Also, in the UA556, pins 3 and 11—which are both control voltage pins—are not connected to _E via a capacitor. What’s the reason for that?

The cap on the control voltage pin is optional. It can help with jitter but it's not a big deal.

[kiouijki]

Hi Carl, I need your help.

I've built the Sniffer XR-71 device, but I'm struggling with some issues and could really use your support.

One problem is that no signal appears on the oscilloscope under normal conditions—unless I touch pin 7 of the NE555 directly with my hand. When I do, a signal appears, but as soon as I let go, the signal disappears and the circuit stops working.

I'm also having trouble with the potentiometers. When I observe the signal on the oscilloscope, only the TRESH potentiometer seems to work—it adjusts the frequency between roughly 23 to 30 kHz. The other potentiometers don’t seem to have any effect. For example, the GAIN potentiometer doesn’t mute the sound, and the speaker stays on constantly.

Also, since I didn’t have an LM555, I replaced it with an NE555.
And because I didn’t have a UA556 either, I used another NE556 instead.

Please let me know what each of the pins labeled A1 and P1 to P9 are for.
If you’d like, I can send you photos of any part of the circuit or check it with the oscilloscope.

I’ll also send you the schematic and PCB layout.

sir connect the A pin under lm556 to A pin betwwen the 2 4066
j3 had 3 pins you need to put jumper or swith to choose mode auto or manual

[kiouijki]

ABOUT P1 TO P9
THIS BOARD HAD 2 DIFRRENT ATTACH BOARDS
1 FOR DISCRIMINATION
2 FOR DISPLAY
YOU CAN CHOOSE 1
NO

[Jafar]

Always start at the beginning, Make sure all power supplies are reasonably correct, nothing else will work without that.

Next task is to get D1a running. PR1 should vary the frequency but I don't know what the frequency range is on this project. When you have D1a running, then I assume D1b adjusts the pulse width via the 20k pot. Again, I don't know the proper range. All this should drive Q1 with a pulse train. This has to work correctly before moving on.

Then you will need to test the other pulses at test points P2, P3 to make sure they are working. Then start looking at signals down the analog path; P1, Tr6, Tr7, etc. All of this requires an oscope.



The cap on the control voltage pin is optional. It can help with jitter but it's not a big deal.

Hi Carl,

I’ve followed and tested all the points you mentioned.

D1a is working, and its frequency is 338 Hz.
D1b is also functioning, and the 20k potentiometer adjusts the pulse width as expected.
I’ve checked test points P2, P3, P1, as well as Tr6 and Tr7 — all of them show valid pulses.
I have an oscilloscope and can send you photos or videos from any point you’d like.
Also, I’d like to ask: if I don’t build the LCD section, will the device still operate properly on its own?

[Jafar]

ABOUT P1 TO P9
THIS BOARD HAD 2 DIFRRENT ATTACH BOARDS
1 FOR DISCRIMINATION
2 FOR DISPLAY
YOU CAN CHOOSE 1
NO

Thanks for your guidance.

I’ve connected pin A under the LM556 to pin A between the two 4066 ICs.
For J3, I’ve used a switch and set it to manual mode.


Regarding the additional boards:

I haven’t built the discrimination or display boards yet.
Can the device still operate properly without using either of these boards?


About the search coil:

I’ve built a coil with 500 µH inductance and 2.3 ohms resistance.
What should be the value of the damping resistor for this coil?
Should I connect the damping resistor in series or parallel with the coil?
If I connect it in parallel, should it be placed at the beginning or end of the coil wiring?

[kt315]

I’ve built a coil with 500 µH inductance and 2.3 ohms resistance.
What should be the value of the damping resistor for this coil?

1K on your board

Should I connect the damping resistor in series or parallel with the coil?

parallel. look a place for it at board. at your pic it is fat resistor setted vertically.

If I connect it in parallel, should it be placed at the beginning or end of the coil wiring?

to both ends of coil. solder damping resistor on board and you will get this connection automatically.