Trebled the range of my pinpointer!!!

[mykaitch]

I was messing around and I thought I would play with the well known 'trick' of sliding a coin along the body of the pp.Without wishing to patronize anybody here, we all know what that does electronically, right ? So I tried it on mine and found that over the 'rx end' and it had a huge effect. So I experimented some and came up with THE RANGE RING, tarah!



You can see a black ring just in front of the buttons. I set the sensitivity with the pot as usual then turn the ring until it tirggers, then back off a fraction. I can pick up a US penny at 4". It's bloody amazing!
I know what you are thinking ; what's in my ring ? Now then, calm down. We'll have no smuttyness on this Forum.




This is the mark 1. I found by changing the length of copper tape I could greatly affect how it works - which is to be expected, but around an inch on my ring was perfect. I told you lot to stop giggling.





If I could (I can't) I would cut a fine thread so that (oh God, here we go again), my ring could slide up and down on a thread which would be nice. As it is though it is magic. Did make one faux pas; I was trying to set it and having trouble - I am left handed and on my third finger.....I have a wedding ring. It really has trebled the range so much so that I won't always want to use it.

(Yes I know that's not a penny in the pic. That wasn't the test coin).

[baum7154]

I just bought one of the Harbor Freight-Centech pin pointers ($13 with a 25% off coupon). There are lots of mods on it primarily having to do with adding a motor/vibrator from a cell phone. Also negative temp compensation, main power switch mods, and indicator LED mods. They also mention a sliding ring mod to increase range so I'm going to try out your trick and let you know how it works. Your idea about using a threaded section to allow fine positioning of the ring is also very good. I will work on that too as I have access to a lathe to cut the threads. There might be some other easier way to achieve the threads from existing common scrap like plastic bottles and mating caps. With the inexpensive price it is enticing to try to optimize this thing.

Regards,

Dan

[mykaitch]

Hi. Since then I found a much better way: I replaced the diode with a transistor wired as a diode. This allows me to make fine adjustments with the 'sensitivity' control that are just as effective as the copper ring idea.

[baum7154]

Hi. Since then I found a much better way: I replaced the diode with a transistor wired as a diode. This allows me to make fine adjustments with the 'sensitivity' control that are just as effective as the copper ring idea.

So are you saying that a the distance improvement you had with the ring was matched by the transistor substitution for the diode? Do you have a picture of the mod? I assume the diode replaced was D2 of the schematic, but I think that is only a polarity protection diode.

It is interesting to note that the detector was originally designed for the motor vibrator, the NTC resistive element, a switch to select the vibe or beeper mode, and C4 to smooth out ripple. The circuit board is etched and drilled for these components. Of these, the most important omission is the NTC resistor as the unit suffers badly from temperature instability. I'm going to install the NTC and the vibe motor this week.

Anyway I did the collar trick and the attached picture is of the mod, some targets used, some detection distances, some dimensional info of the Brass mod collar, and some information on the optimum placement of the collar on the detector rod.



The detection distances were dependent upon the setting of the sensitivity threshold and that was unstable over time. The best detection I saw was about 4" on the nickel but, with detection, the unit tended to lock up so that is an impractical operating point. Therefore the distances shown are ones that were stable with the greatest range. I paid particular attention to the behavior of the detection zone at the end of the rod and how far up the side of the rod it extended. This was done with the end of the brass collar nearest to the case set from 1/2" to 2" from the rod shoulder on the case as a reference point. It was moved in .1" increments and the best performance point was at 1.630" from the rod shoulder. This equates to the far end of the collar actually being located 2.310" from the rod shoulder of the case. This will most likely vary from unit to unit as the production tolerances for the cases and rod antennas are likely not very tight. I also noticed that the end of the rod antenna is actually about 5/16" in from the outer end of the cap so that should be added to the End On Detection Distances in order to be accurate.

The targets used:

A US nickle

A small vial of placer flakes about the volume of a book match head.

A 1/4" X 1/4" X 0.004" thick aluminum piece of pop can

The last two targets I used because they mimic small gold.

Larger targets were detected at much greater distances. A 1/2" X 1/2" X 0.004" piece of aluminum pop can is seen at 2".

I'll post results of the stability mod later this week.

Regards,

Dan

[baum7154]

Hi. Since then I found a much better way: I replaced the diode with a transistor wired as a diode. This allows me to make fine adjustments with the 'sensitivity' control that are just as effective as the copper ring idea.

What pinpointer do you have? It doesn't sound like the one I have.

[mykaitch]

Here are some pics from an old post and the schematic. You seem to have a ring of copper but you should only use a small piece. In my version the ferrite rod enters the main body a short way so the ring with about 1cm of copper inside is really over the ferrite.
However...with the mod to the sch...the led will flicker and get brighter the closer you get to the target and the sound will increase, so you can adjust it very finely. I STILL have not solved the temp issue; for now I can switch in a different resistor to the sense control to get around it - it ain't nice but it works.
[IMG]file:///C:\DOCUME~1\Mike\LOCALS~1\Temp\msohtmlclip1\01\cli p_image002.gif[/IMG]
pp_sch Copy.pdf

[baum7154]

Thanks for the clarification. My detector circuit is very different from yours. I'll try just the metal strip to see if it will work too.

[baum7154]

Modded the Centech 97245 detector as follows:

1. Moved the ground end of the LED to the output of the 2N7000 FET - Originally the LED was lit when ever the power was on AKA a Flashlight. This mod makes the LED a signal strength indicator and a threshold setting indicator as it is only on when threshold is set too sensitive or a target is detected.

2. Doubled the piezo limit resistor to 150 ohms - reduces power consumption and makes the piezo more bearable.

3. Added a pager vibrator motor and a 180 ohm limit resistor in series. Provides tactile feedback and silent operation around others.

4. Installed a DPDT select switch controlling 'Vibrate' or 'Audible' indication of detection.

5. Installed a 100 ohm thermistor to help with stability.

6. Installed a .22uf cap to filter out ripple on the comparator input.

7. Reset internal range pot in the Sensitivity control part of the circuit to allow proper range of the external Sensitivity pot.

8. Replaced the TL062 dual op amp with a TL082 dual op amp. Improved stability.

The detector now gives varying audio tone going low when a target is detected and target detection is always accompanied with brilliant LED light. The light is a great help in presetting threshold for more depth as you can set for very low illumination of the LED in the idle state.

Note: The original board comes etched, drilled, and marked for most of these component changes but they were left out in manufacture presumably to cut cost.

The jury is still out on the sliding ring trick originally posted. I think it works on detectors that have not been optimized with mods. It does this by mechanically bringing the detector closer to its sensitivity threshold. The sliding ring may have a benefit in reshaping the field around the ferrite rod but I have not yet been able to prove this to be true. If it does then it may still be worthwhile.

Detection distance of this detector on a 1/4" X 1/4" piece of aluminum can is now 0.75". US Nickle is 2.375"

[mykaitch]

Modded the Centech 97245 detector as follows:

1. Moved the ground end of the LED to the output of the 2N7000 FET - Originally the LED was lit when ever the power was on AKA a Flashlight. This mod makes the LED a signal strength indicator and a threshold setting indicator as it is only on when threshold is set too sensitive or a target is detected.

2. Doubled the piezo limit resistor to 150 ohms - reduces power consumption and makes the piezo more bearable.

3. Added a pager vibrator motor and a 180 ohm limit resistor in series. Provides tactile feedback and silent operation around others.

4. Installed a DPDT select switch controlling 'Vibrate' or 'Audible' indication of detection.

5. Installed a 100 ohm thermistor to help with stability.

Where in the circuit did you do this ?


6. Installed a .22uf cap to filter out ripple on the comparator input.

7. Reset internal range pot in the Sensitivity control part of the circuit to allow proper range of the external Sensitivity pot.

8. Replaced the TL062 dual op amp with a TL082 dual op amp. Improved stability.

The detector now gives varying audio tone going low when a target is detected and target detection is always accompanied with brilliant LED light. The light is a great help in presetting threshold for more depth as you can set for very low illumination of the LED in the idle state.

Note: The original board comes etched, drilled, and marked for most of these component changes but they were left out in manufacture presumably to cut cost.

The jury is still out on the sliding ring trick originally posted. I think it works on detectors that have not been optimized with mods. It does this by mechanically bringing the detector closer to its sensitivity threshold.

Yes, I agree. When I modded mine the same happened (and with the led function too)

The sliding ring may have a benefit in reshaping the field around the ferrite rod but I have not yet been able to prove this to be true. If it does then it may still be worthwhile.

Detection distance of this detector on a 1/4" X 1/4" piece of aluminum can is now 0.75". US Nickle is 2.375"

Nice.

[baum7154]

The circuit board has a position marked 'NTC' (Negative Temperature Compensation)on it for placement of the thermistor. The NTC is paralleled by a 100 ohm resistor and this pair is in series with the Sensitivity trim adjustment. On other models that is where I would put the compensation.

Regards

Dan