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Hello,
I just completed my Hammerhead and thought I would share with the group in case it might help someone else. I really had a lot of fun with this project. Carl's article was great and I learned a lot about PI detectors.
I completed the PCB using Silver Dog's great kit that was easy to build. I followed the article and built the board in stages testing the stages as I went along. I set the damping resistor using my scope, decreasing the resistance with a pot across the coil until the spikes on TP4's wave form just disappeared. This ended up being a 400 ohm resistor. I checked the rest of the wave forms and they were essentially in line with Carl's article.
Except for the enclosure, pcb, wire, grip, electronics and styrene stock, the detector was mostly constructed from fittings and 1/2" schedule 40 pvc pipe purchased at Lowes. I also glued a fiberglass rod purchased from Tap Plastics into the pvc stem to stiffen it. The arm rest and stand were made out of a 4" pvc coupler cut length-ways and shaped with a file. The detector breaks down in the middle of the stem so I will be able to transport it to the beach for an upcoming trip.
Based on my experience with regen radios, I also glued (JB Weld) a 1/16" copper sheet to the top inside lid of the pcb enclosure (drilling holes for the pots) and grounded it to VB+. This seemed to help the detector be reasonably quiet.
For the coil housing, I used two styrene ceiling medallions from the ceiling fan department at Lowes for $7.98 each. I made the coil stem clamp out of styrene strips glued together. I made a slight mistake when I wound the coil and ended up with 260uH and about 4.5 ohms resistance with an 8" diameter (awg 30 wire). The cable to the pcb is RG-62/U. I mostly followed BBSailor's great article to construct the coil.
Power is from 8 x 1.5v AA's in a battery pack beneath the main enclosure.
The detector works pretty good, detecting a U.S. quarter at about 7", but the performance is not as good as other folks have obtained. I plan on building another coil with more inductance to see if I can increase the depth.
I agree with other posters that a scope is probably a must to construct the Hammerhead. Although I was able to make all of the adjustments called for in the article with my multimeter, setting the damping resistor and checking the wave forms should be done with a scope. I would also advise anyone constructing the Hammerhead to look at the photos of the completed pcb posted by members, especially the one posted by Carl, to see how the jumpers are configured. Of course, you can also just follow the schematic.
This is a great forum and just about every post is worth reading.
Photos below.
Dan
I just completed my Hammerhead and thought I would share with the group in case it might help someone else. I really had a lot of fun with this project. Carl's article was great and I learned a lot about PI detectors.
I completed the PCB using Silver Dog's great kit that was easy to build. I followed the article and built the board in stages testing the stages as I went along. I set the damping resistor using my scope, decreasing the resistance with a pot across the coil until the spikes on TP4's wave form just disappeared. This ended up being a 400 ohm resistor. I checked the rest of the wave forms and they were essentially in line with Carl's article.
Except for the enclosure, pcb, wire, grip, electronics and styrene stock, the detector was mostly constructed from fittings and 1/2" schedule 40 pvc pipe purchased at Lowes. I also glued a fiberglass rod purchased from Tap Plastics into the pvc stem to stiffen it. The arm rest and stand were made out of a 4" pvc coupler cut length-ways and shaped with a file. The detector breaks down in the middle of the stem so I will be able to transport it to the beach for an upcoming trip.
Based on my experience with regen radios, I also glued (JB Weld) a 1/16" copper sheet to the top inside lid of the pcb enclosure (drilling holes for the pots) and grounded it to VB+. This seemed to help the detector be reasonably quiet.
For the coil housing, I used two styrene ceiling medallions from the ceiling fan department at Lowes for $7.98 each. I made the coil stem clamp out of styrene strips glued together. I made a slight mistake when I wound the coil and ended up with 260uH and about 4.5 ohms resistance with an 8" diameter (awg 30 wire). The cable to the pcb is RG-62/U. I mostly followed BBSailor's great article to construct the coil.
Power is from 8 x 1.5v AA's in a battery pack beneath the main enclosure.
The detector works pretty good, detecting a U.S. quarter at about 7", but the performance is not as good as other folks have obtained. I plan on building another coil with more inductance to see if I can increase the depth.
I agree with other posters that a scope is probably a must to construct the Hammerhead. Although I was able to make all of the adjustments called for in the article with my multimeter, setting the damping resistor and checking the wave forms should be done with a scope. I would also advise anyone constructing the Hammerhead to look at the photos of the completed pcb posted by members, especially the one posted by Carl, to see how the jumpers are configured. Of course, you can also just follow the schematic.
This is a great forum and just about every post is worth reading.
Photos below.
Dan
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