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I am attempting to build the Hammerhead PI detector. I have most of the parts and am looking toward the searchcoil. I know the instructions call for an 10 inch searchcoil, but I am after some deep civil war projectiles and Hays has an 18x14 pi searchcoil body that I would rather use. I know that I may have to make a few changes to the circuitry. According to the instructions R1-R4 would need to be modified to give a lower clock frequency, such as 100Hz. Does R1-R4 mean those two resistors, or R1; R2; R3; and R4? What I am asking is what values should I use for R1; R2; R3; and R4? Would Q3 and R11 need to be heat sunk? The instructions also call for a ten inch searchcoil using 26 AWG enameled wire with 26 turns. Would I use the same wire and same number of turns, or different size wire and a different number of turns? One other question I am not sure about is on the potentiometers. I know some are mounted on the circuit board and some are mounted on the detector body. Of course the audio is on the body of the detector, but which other potentiometers need to be mounted on the detector body for easy adjustments? I hope these questions are not to complex, and my electronic experience is limited, but with a little help I think maybe I can get this detector up and working.
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Working backward... Besides on/off/volume, I think most people put the sample delay on the box, probably threshold as well. Freq doesn't get adjusted much, pulse width is nice to have on the box.
As the coil gets bigger, turns get fewer. A 1-meter square coil is 8 turns I think. An 18x24 will be somewhere in between, you will need to experiment. Wire size is not a big issue, 18-26 AWG should be fine.
Heat on Q3/R11 can increase with longer pulse times, so heat sink Q3 and use a higher wattage R11 (or multiple parallel resistors).
I have values for R1-R4 at home, will try to post tonite.
- Carl -
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Thank you Carl for the information. You are very helpful.Comment
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OK, I left R1 & R2 alone.
R3=2k pot, but I didn't have a 2k so I used a 1k.
R4=680 ohms
C8=0.1uF
This cuts freqs. roughly by 1/10th, so the range should be 90-230 Hz. Not sure what the pulse width range is though, I'd have to measure. Or, you can calculate it if you have the timing equations for the 555, which are very simple.
- CarlComment
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