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I read a couple of do it yourself metal detector write ups in the web as well as the one in the Instructables page that looks exactly like the one on a page. So I decided to make my own too. However I made up most of it as I went around because the information on the web was incomplete or not very precise. So I decided to make one with exact measures and post it here so that everyone who wants to try it can be confident that they are making something that will work. Here's my first Instructable so be nice :)
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Signing UpStep 1Build the circuit board
When i was looking in the internet for a metal detector circuit, I saw a couple of desing but they where not specific enough to go into detail and i figured a average person with no knowledge of electronics cant figure it out, so after much joining the dots i finally made one and decided to share it here. all the circuit design is from the link provided "easytreasure". The pictures of my device are mine.
This work is in the Public Domain.
The circuit board is the heart of the detector. There are 2 different styles out there for the home made version. I based my design on this circuit shown here. I build it to the same layout of the circuit, but not necessarily of the print out supplied. in other words, is the same circuit but looks different from the paper. The circuit I copied from this page. I did not design this circuit:
http://www.easytreasure.co.uk/bfo.htm
And it really easy. the parts can all be found on Radioshack for about 10$ total or ordered on the web for about 1.50$ total+shipping. Beware that I emptied the Radioshack out of capacitors and actually had to go to another Radioshack to find the missing one's.
here's a part list:
Power source:
Any 9v battery PP3 is ideal. Remember to also buy a 9V connector for your battery
Capacitors:
2 off 220uF 16v electrolytic.
5 off .01uF polyester.
5 off .1uF polyester.
Resistors:
All resistors 1/4 watt 5%
6 off 10k
1 off 1K
1 off 2.2m ===== 2.2 Mega ohm
2 off 39k
The resistors can be 1/8 of a watt if you use 9V because according to my calculations the highest wattage going through the smallest resistor in the circuit is about .080 watts, and the 1/8 handle up to .125 watt. Radio Shack did had most of them but there was some that where hard to find. so you can either buy some and add the values up to the desired value, or buy bigger and use the Resistance division formula (Total R= 1/r1 +1/r2 + etc). I bought a small bag of 1/8 watt resistors that comes with like 120 resistors from all ranges possible to mankind (maybe not that much) but it had all necessary and now I got a big inventory of surplus resistors. it was the most expensive at 12$.
The transistors are npn. Radio Shack had this small package that comes with 15 NPN resistors for multipurpose general use, and they work fine. You can make 2 circuits and still have some to spare to in case you mess up and need more. Its about 2.50$ for the package.
You can also buy a PCB board to make the circuit and soldering iron (10-15$) 25 watt will do and soldering thin. You can use the cheap stuff for this, don't buy the silver one, too expensive, no difference in this project.
When you're there, get the cable for the coils. You will need about 4 FT of small 22 gauge DUAL wire (that is two wires joined, else you need 8 ft) and some 26 gauge for the coils or whatever you wana use. I bought a small bag that had 3 rolls of insulated enamel wire, 30, 26 and 22 AWG.
The following information, references and quotes are from the Designer website
http://www.easytreasure.co.uk/bfo.htm
"
Coil A = Search coil: Coil B = Reference coil: NC = No connection: B+ = Battery + 9V PP3 or similar : B- = battery -
Notes for the electronics beginner.
2 off 220uf / 16v Electrolytic : These are 220 microfarad / 16v working voltage. You can use a higher working voltage but not less. Higher working voltage capacitors work just the same but they get physically bigger. They have a negative lead that must be connected to the battery - track. These components must go in the correct way round.
5 off .1 and .01 polyester : These also have a working voltage. 63 volt in quite common and will be ideal. If you want to use the pcb layout above you will need capacitors with 5mm lead spacing. .1 can be marked as .1 or 100n or sometimes 104 : .01 can be marked as .01 or 10n or sometimes 103. These components can go in any way round.
All resistors 1/4 watt 5%: These are general purpose carbon film resistors with a 5% tolerance and rated at 1/4 watt. You could use resistors of a higher wattage as this does not affect the working they just get bigger. 1 watt or bigger will not fit on the board. These components can go in any way round.
Transistors: The bc 184b transistor is described has Audio, low current, general purpose NPN . These are quite easy to get in the UK but may be difficult to get in other countries. There are hundreds of types of small plastic NPN transistors available around the world and just about all will work in this circuit. You will have to be sure of the pinouts though. You can get the pinouts for most transistors from manufacturers websites. This will be the most likely problem area when building this project. These components must be connected correctly. PNP types won't work.
"
I used a Car hands free headset to canibalize the speaker to use for this circuit.
This work is in the Public Domain.
The circuit board is the heart of the detector. There are 2 different styles out there for the home made version. I based my design on this circuit shown here. I build it to the same layout of the circuit, but not necessarily of the print out supplied. in other words, is the same circuit but looks different from the paper. The circuit I copied from this page. I did not design this circuit:
http://www.easytreasure.co.uk/bfo.htm
And it really easy. the parts can all be found on Radioshack for about 10$ total or ordered on the web for about 1.50$ total+shipping. Beware that I emptied the Radioshack out of capacitors and actually had to go to another Radioshack to find the missing one's.
here's a part list:
Power source:
Any 9v battery PP3 is ideal. Remember to also buy a 9V connector for your battery
Capacitors:
2 off 220uF 16v electrolytic.
5 off .01uF polyester.
5 off .1uF polyester.
Resistors:
All resistors 1/4 watt 5%
6 off 10k
1 off 1K
1 off 2.2m ===== 2.2 Mega ohm
2 off 39k
The resistors can be 1/8 of a watt if you use 9V because according to my calculations the highest wattage going through the smallest resistor in the circuit is about .080 watts, and the 1/8 handle up to .125 watt. Radio Shack did had most of them but there was some that where hard to find. so you can either buy some and add the values up to the desired value, or buy bigger and use the Resistance division formula (Total R= 1/r1 +1/r2 + etc). I bought a small bag of 1/8 watt resistors that comes with like 120 resistors from all ranges possible to mankind (maybe not that much) but it had all necessary and now I got a big inventory of surplus resistors. it was the most expensive at 12$.
The transistors are npn. Radio Shack had this small package that comes with 15 NPN resistors for multipurpose general use, and they work fine. You can make 2 circuits and still have some to spare to in case you mess up and need more. Its about 2.50$ for the package.
You can also buy a PCB board to make the circuit and soldering iron (10-15$) 25 watt will do and soldering thin. You can use the cheap stuff for this, don't buy the silver one, too expensive, no difference in this project.
When you're there, get the cable for the coils. You will need about 4 FT of small 22 gauge DUAL wire (that is two wires joined, else you need 8 ft) and some 26 gauge for the coils or whatever you wana use. I bought a small bag that had 3 rolls of insulated enamel wire, 30, 26 and 22 AWG.
The following information, references and quotes are from the Designer website
http://www.easytreasure.co.uk/bfo.htm
"
Coil A = Search coil: Coil B = Reference coil: NC = No connection: B+ = Battery + 9V PP3 or similar : B- = battery -
Notes for the electronics beginner.
2 off 220uf / 16v Electrolytic : These are 220 microfarad / 16v working voltage. You can use a higher working voltage but not less. Higher working voltage capacitors work just the same but they get physically bigger. They have a negative lead that must be connected to the battery - track. These components must go in the correct way round.
5 off .1 and .01 polyester : These also have a working voltage. 63 volt in quite common and will be ideal. If you want to use the pcb layout above you will need capacitors with 5mm lead spacing. .1 can be marked as .1 or 100n or sometimes 104 : .01 can be marked as .01 or 10n or sometimes 103. These components can go in any way round.
All resistors 1/4 watt 5%: These are general purpose carbon film resistors with a 5% tolerance and rated at 1/4 watt. You could use resistors of a higher wattage as this does not affect the working they just get bigger. 1 watt or bigger will not fit on the board. These components can go in any way round.
Transistors: The bc 184b transistor is described has Audio, low current, general purpose NPN . These are quite easy to get in the UK but may be difficult to get in other countries. There are hundreds of types of small plastic NPN transistors available around the world and just about all will work in this circuit. You will have to be sure of the pinouts though. You can get the pinouts for most transistors from manufacturers websites. This will be the most likely problem area when building this project. These components must be connected correctly. PNP types won't work.
"
I used a Car hands free headset to canibalize the speaker to use for this circuit.
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Any ideas what I might be doing wrong?
can i have your inductance value of both coil,, coz i dont have anameled with 26 AWG of diameter ,, i just have 0.2mm.. i will try to match your value with this diameter wire of mine,, pleeeeeeeeeeeeeeez reply me,, TQ =)
can i use any other ic instead of cs209a n making single chip metal detecter.
Just don't know what I'm doing wrong. Can You explain whats happening in this circuit so that I can trouble shoot it better. All so I used the NPN 4011 and was wondering if there are different values of the same transistor or some thing.
Any help will be greatly appreciated.
Try a 2n2222 or a 2n3904 transistors, easy to find anywhere.
I already explained what goes on in this circuit. The top small Capacitor-Inductor (LC) oscillates at the same frequency as the bottom LC circuit. They cancel each other out, when metal aproaches the bottom inductor, it changes the freq, and that difference peak pulse is aplified from left to right, trough each transistor, then to the speaker.
thanks for this instructable. Can I use this method to make a security system like those we see in airports, those which look like doors that passengers pass to have been checked.
thanks!! for clarify some things the other site was weird....
i was wondering why you use "off" in the parts list?
why not use x instead lol
(2 off 220uF 16v electrolytic) (2x 220uF 16v electrolytic)
i took an electronics class for 2 years (2hours 30min a day) when i was in high school and never seen a parts list with "off" describing how many you need...
people dont just go around saying "i need 3 off loaves of bread" or
" 2 off cans of beans" lol...
off is describing if something is on or not lol.....
people also dont say i want 5x oreos 1x cup of milk lol
off just didn't make sense when used in the parts list
even if you got the list from the other site i would of fixed it. lol
(sorry im not trying to be rude or anything)
(lol electronics class was the highlight of my day any other class and im bored to death)....................
I know, i am an engineer
so what have you found so far with your metal detector?
im sure everyone else is curious if you found anything with this home made metal detector.
I used it to find a spoon the professor buried to see if it worked. I used to find come screws i lost while working on a motorcycle in the grass. I may upgrade it since I'm now working making mine detectors for the military and they use metal detectors as well as Ground Radar.
If a modern metal detector is a 3 ghz computer, this is a basic calculator, not even a TI-83