Metal detector for finding archery arrows

[Mothough]

ok. give your facebook link. i must look that you are really archer. i must see on your page -
hunting with the arbalests, you with dead animals, etc. i wildy begin to doubt in your primary passages
because you did rerun on gold matter at end.

Ehm? The offtopic stuff was not by me. Just to clarify, I do not hunt with arbalest nor kill animals. I'm a hobby archer using a recurve bow.

PI's are typical and you can use any building guide, bara too, for surf pi.

Actually, thats what I try to do.

Figured out the pulse generation. I did misinterpret the different pulses. I thought the first 4093 (IC4C) output is already the sampling pulse but it is not.
Furthermore there may be a value error in the schematic mentioned above. The delay pot P4 is only 10k, with the additional 5k1 from R25 I cannot get the delay pulse long enough. In a non-pro version of the schematic it is a 100k pot. With that combination I can easily achive 20?s of delay pulse mentioned in the Baracuda build guide.

Just to recap the different functions of the schmitt triggers in the pulse generation stage:
*) IC4C just creates the delay pulse used to offset the first sample pulse.
*) IC4A creates the first sample pulse with a width of about 40?s.
*) IC4D creates a second delay pulse to offset the second sample pulse.
*) IC4B creates the second sample pulse with a width of about 40?s.

Now lets check once again the RX preamp stage and then continue with building the sampling integrator.

Anyone know by chance how much gain the preamp stage should have? Like voltage swing of the signal. It seems I'm only getting about 2Vpp which seems quite low?

[Polymer]

Hello Mothough,

I would recommend the MPP E from Silverdog.
You can easily adjust many parameters with this one - for example the Pulse Width, Delay ... to experiment what works best for finding your stainless steel tips.

I work with shorter Pulse Widths and delays. Testing with nickels and small gold rings, these I can detect easily.
A stainless steel ring I have is much harder to detect well, my delay has to below 12us for that.

I can only guess at what delay times your arrow heads may need.

You probably need to experiment a bit to find out. You may actually enjoy experimenting, learning as you go.
I do, with some cursing here and there of course ...

I believe the arrow heads will be more on the surface than under the ground, so one problem less
Correct me if I am wrong here.

Cheers, polymer

[gravelmonkey]

Instead of trying to detect stainless steel; would a ring of self adhesive copper tape around the shaft help for detection purposes?

[Skippy]

He's trying to find many hundreds of dollars worth of arrows that are already lost., though obviously there will be ongoing losses in the future.

However, it's an interesting challenge , how to 'label' the arrow without compromising it in terms of weight, balance, aerodynamics, etc. How to get the maximum detectability for the minimum amount of added material.

I'm going to rummage in my bike spares box, I think there's some stainless steel bolts that are comparable to the arrow points. If so, I'll try and get some measurements on them.

[kt315]

I would recommend the MPP E from Silverdog.
---
leave it out. he does not want to waste a money on the PCBs. he wants to learn a potencial of PI making parts on breadboard.
he is just 'wife kitchen table reseacher'. i think he is still one pakistani guy. also he REFUSED to share pics with him in his hobby
because there is not hobby, just 'a wish'.

[green]

he is just 'wife kitchen table reseacher'.

my kitchen table. Fly tying one side, metal detecting the other.

[Mothough]

I would recommend the MPP E from Silverdog.

Thanks for the recommendation. I'll probably end up getting some kind of pcb in the end if I get promissing results.

You probably need to experiment a bit to find out. You may actually enjoy experimenting, learning as you go.

Yep, I'm currently trying to figure out what would be feasable with DIY detectors.

I believe the arrow heads will be more on the surface than under the ground, so one problem less

Correct, they just slip into sward. If they are shot steep enough to pierce the ground they stick up and are easily spottable.

Instead of trying to detect stainless steel; would a ring of self adhesive copper tape around the shaft help for detection purposes?

Very good point. Actually, they make arrow shafts containing carbon aswell as aluminium but they are mostly used in professional competition.
However, if detecting stainless turns out to be too difficult, copper bands or similar would be a feasable solution since all below 1-2grams are not really noticable in hobby archery. Many hobby archers mark their arrows with multi color insulation tape to disdinguish them.

He's trying to find many hundreds of dollars worth of arrows that are already lost., though obviously there will be ongoing losses in the future.
However, it's an interesting challenge , how to 'label' the arrow without compromising it in terms of weight, balance, aerodynamics, etc. How to get the maximum detectability for the minimum amount of added material.

All arrows which are in the ground for too long are practically worthless since degretation is quite an issue under wet conditions. The stainless steel head will be the only usable by then, which in itself is not worth de effort to search for them.

he does not want to waste a money on the PCBs. he wants to learn a potencial of PI making parts on breadboard.
he is just 'wife kitchen table reseacher'. i think he is still one pakistani guy. also he REFUSED to share pics with him in his hobby
because there is not hobby, just 'a wish'.

I'm not a facebook user, nor will I post any other social media nor pictures of me here, sorry.
Best I can do to ease your paranoia is a picture of my archery equipment:
And the current state of the breadboard prototype

I'm currently still puzzled a bit by the preamp stage. Doesn't seem quite right yet.

[green]

I'm currently still puzzled a bit by the preamp stage. Doesn't seem quite right yet.

Think you won't see stainless steel points at amplifier out. Should be able to see coins. Need to add integrator to see point's.

[kt315]

good. i got now. thank you. 1 question. why you do underwater PI detector?
in my opinion HH is better. also, you will dig all metal because PI does not have a discrimination FERROUS-UNFERROUS.

[Mothough]

Think you won't see stainless steel points at amplifier out. Should be able to see coins. Need to add integrator to see point's.

Oh, okay. Does a 2Vpp level seem right to you? Shouldn't it be more near the +/-5V rails. 2Vpp seems to me like almost no gain?

good. i got now. thank you. 1 question. why you do underwater PI detector?
in my opinion HH is better. also, you will dig all metal because PI does not have a discrimination FERROUS-UNFERROUS.

Just because it looked the easiest to build and I had all parts already available and there were different schematic versions I could somehow understand available.

[green]

Oh, okay. Does a 2Vpp level seem right to you? Shouldn't it be more near the +/-5V rails. 2Vpp seems to me like almost no gain?

Don't have a Surf PI so just some thoughts. If you are reverencing reply#33. NE5534 should swing about +-2.5V with +-5V supply. Don't know where CH1 scope zero is. I'm with you, doesn't look right to me.

[Mothough]

All channel zero markers are in the middle of the screen and stack below the CH4 marker.

Just noticed an issue while adjusting R10 offset pot for 0V DC offset (Step 5 of the Baracuda bulding guide).
Got about 0.85V on the NE5534 output which I can only compensate about 40mV up and down by turning the pot from end to end. Maybe I fried the opamp.

Will swap it when I get the integrator stage going.

Also tried with a chunk of iron and the recovery signal trace quite drastically bends. At least this looks quite promissing. Maybe my coil is still not right since the trace starts to recover after 3us and is already done in about 6us.

Surf Detector on Youtube shows much longer recovery time of about 100us using his coil:

Furthermore my delay pulse (CH2) does start way later compared to his delay pulse also CH2
His sampling pulse then coveres the recovering period of CH1 like it should?
When my recovery pulse (CH3) hits, the signal trace (CH1) is already all the way back up, which seems not right. Coil way too fast?

[green]

Looking at https://www.geotech1.com/forums/atta...7&d=1604945664 if zero is in center, should be able to adjust offset pot so amplifier out goes to zero(center screen)after signal has decayed. Don't think coil is causing problem.

[Mothough]

Exactly, thats the 0.85V I was talking about and Surf Detector's screenshots show exactly what you say. Will have to investigate further.

[Mothough]

Looks like the NE5534's I have in stock are counterfeit. Bummer! They just behave like a bad quality jelly bean opamp with no offset trim. The pins in question seem to be NC.

Tests with a pin compatible opamp results in much more reasonable gain and allows offset trim. Sadly this opamp somehow seem to pick up huge amounts of 50Hz hum. Will have to find a proper replacment.

I think AD711, OPA134, OP27 or OPA604 may be also suitable for the job.

Will keep you posted!