yourownfree
New Member
- Joined
- Jan 30, 2026
- Messages
- 4
The metal detector was inexpensive. It was a module in a cube and you could not see what was inside the cube. You had to wind your own coil and put the rest of the parts together. I used an old broomstick for the structure and taped everything on the handle. It was a blast. It worked ok but I had nothing to compare it to since I never owned or tried any other. I can tell you it was a BFO type. To hear the tone you had to carry a transistor radio tuned to a local radio station and then adjust the pot on the detector until it transmitted on frequency with the radio station. It was annoying as the station may be too powerful and you had to tune to another. besides the little detector would not completely get rid of the station so you had a mix of radio station in there. So the theory is the MD would transmit and beta against the radio station frequency and the difference was the audio frequency you would hear and you could vary that with the pot to your liking. So that is what got me started in metal detecting. I built a few more with just parts and pieces no modules, designed them myself. I made one once to go to the park after a carnival and it worked in the air but when i got it there in real life it was worthless. I didn't want to be embarrassed because there were others there too so i kept pretending it worked and I found more by looking on the ground. It was also a BFO detector. I swore I'd never make another after that and I haven't. I was about 16 years old then. Funny how life changes you. I have been designing other things in my life just for fun. I built a few AM broadcast band radio transmitters, some with vacuum tubes/valves depending on where you live what you call them. I built small ones that go close to 10 miles, and a couple FM broadcast band transmitters. One of those I did it all with one transistor and played 8 track tape audio through it a a distance of 3 miles. The secret to those units to get out farther, and it took me years with trial and error to perfect it. For me that was a challenge at that time. The secret was all in the antenna. It had to be tuned to the frequency I was using. Simple way of describing it.
Lately I have been thinking of building a metal detector for my sister and not a crappy BFO type. I'm leaning more toward the Pulse induction. I have not built it yet as I'm still designing. Taking a step back for a moment I need to build a vehicle loop sensor that will open a gate and a residential home. While I was pondering that the bfo diagram popped in my head but I didn't want to use that so I thought about it for some time so I could change it to work for me. I have that figured out now but in the process I actually came across an idea for a BFO type metal detector. I don't know as it was not my intention to make one as I need to be focused on the gate opener. As I slipped into a daze thinking and redesigning in my mind I have figured out a way, in theory to eliminate the fixed oscillator in the metal detector and yet still behave as a BFO. a BFO metal detector has two oscillators running at the same frequency. One uses the search head coil as the determining frequency and the other is a fixed small coil which resides in the box that determines the othe other oscillators frequency. You can adjust that oscillator so that its not exactly right on the money with the search head coil frequency. When that happens you actually can hear the difference between the two as audio, mixing the two signal together (one oscillator beating against the other) notice BFO, beat frequency oscillator. Anyhow I have not yet tried it but I am thinking very seriously about doing so to eliminate the fixed oscillator. Yeah right you might say. it will run on one coil and not really be a beat frequency oscillator unit anymore. It will be a NBFO (not a beat frequency oscillator) unit. I think it will perform the same but I'm not sure or not. I wont give you details here at the moment as how that is to be done. After I put it together and see if it works and it should, then I will reveal how it works and another story about how it came about. Schematics and all will be revealed at that time. it wont be complicated as I want to make it builder friendly. The bottom line is this is my hobby of enjoyment, building things, redesigning them as well. I like to look at schematics as it's eye candy for me. It would be nice if there were a dedicated area in Make it or fix it yourself, of schematics and manuals. one of do it yourself or home built units and one of commercial units. I am a newbie here and first post and there is a lot going on here on this site. I'm not sure exactly where I fit in yet. I'm not much for actual md hunting. I did read the article about electrolysis and have already done that. I used a nine volt battery a penny and a nickel. I transferred the penny to coat the nickel to the same color as the penny. I saw potential here in making a unit that everyone could build with schematic that would not get hot and be adjustable with a readout and settings. For now I'll start with the detector and see how it goes. cheers Ernie
Lately I have been thinking of building a metal detector for my sister and not a crappy BFO type. I'm leaning more toward the Pulse induction. I have not built it yet as I'm still designing. Taking a step back for a moment I need to build a vehicle loop sensor that will open a gate and a residential home. While I was pondering that the bfo diagram popped in my head but I didn't want to use that so I thought about it for some time so I could change it to work for me. I have that figured out now but in the process I actually came across an idea for a BFO type metal detector. I don't know as it was not my intention to make one as I need to be focused on the gate opener. As I slipped into a daze thinking and redesigning in my mind I have figured out a way, in theory to eliminate the fixed oscillator in the metal detector and yet still behave as a BFO. a BFO metal detector has two oscillators running at the same frequency. One uses the search head coil as the determining frequency and the other is a fixed small coil which resides in the box that determines the othe other oscillators frequency. You can adjust that oscillator so that its not exactly right on the money with the search head coil frequency. When that happens you actually can hear the difference between the two as audio, mixing the two signal together (one oscillator beating against the other) notice BFO, beat frequency oscillator. Anyhow I have not yet tried it but I am thinking very seriously about doing so to eliminate the fixed oscillator. Yeah right you might say. it will run on one coil and not really be a beat frequency oscillator unit anymore. It will be a NBFO (not a beat frequency oscillator) unit. I think it will perform the same but I'm not sure or not. I wont give you details here at the moment as how that is to be done. After I put it together and see if it works and it should, then I will reveal how it works and another story about how it came about. Schematics and all will be revealed at that time. it wont be complicated as I want to make it builder friendly. The bottom line is this is my hobby of enjoyment, building things, redesigning them as well. I like to look at schematics as it's eye candy for me. It would be nice if there were a dedicated area in Make it or fix it yourself, of schematics and manuals. one of do it yourself or home built units and one of commercial units. I am a newbie here and first post and there is a lot going on here on this site. I'm not sure exactly where I fit in yet. I'm not much for actual md hunting. I did read the article about electrolysis and have already done that. I used a nine volt battery a penny and a nickel. I transferred the penny to coat the nickel to the same color as the penny. I saw potential here in making a unit that everyone could build with schematic that would not get hot and be adjustable with a readout and settings. For now I'll start with the detector and see how it goes. cheers Ernie
