Hi all I am new to this forum but not so new to detecting but I have some questions regarding a metal detector I purchased just to get back into the hobby after about a 18yr break, The questions are mainly Circuit related so hence the post in the tech section.
OK I purchased a very cheap metal detector for £22 off ebay that is made by Maplin and is a Maplin L45BH the £22 I paid is a lot cheaper than the maplin price and for a cheapo detector is quite good with good depth and not to bad discrimination.
Anyway I was unpleased with a few things on it so I am trying to modify it a bit.
The first thing I did was to add some white paint to the position recesses of the Volume/Sensitivity and Discrimination knobs as in direct sunlight it was hard the see where you had them set as the resses was the same color as the knob BLACK.
The second thing I wanted to try and modify was the analogue meter as it was either always 0 or 10, in other words it would be 0 when nothing is detected and then 10 when you detect something, now correct me if I am wrong but to me a meter is supposed to go up in stages according to the depth of the item so an item at 1" would be 10 whereas an item at 15" would be about 0-1. This is where the screw drivers came out and I took it all to bits and on the circuit board are 2 Variable resistors, so I thought this must have something to do with setting the meter so I turned them a little bit and guess what there was no change in the meter but now it hardly detects any copper the copper needs to be 1mm before it detects it so I need to back those off again or increase them.
Anyway my main concern at the moment is to get this meter working properly but I am lost as to what kind of detector this is out of either a BFO or VLF I know it is not a PI as it only has one tone.
While I have it in bits on the table I decided to research the numbers from the SMD chips on the circuit as the circuit is 90% SMD components it has a total of 5 SMD chips, 2 are LM339 Quad Differential Comparators, 2 are GZL1403 or 064C Low Power JFet OppAmps and the other is a HEF405381 or 5381 Triple 2-Channel Multiplexer/Deplexor but I have no Idea from the above componets used what kind it is is it BFO or VLF?
Any help on the kind of detector it is from the above used components would be great as then I will know what I am working with.
I was thinking about a Small Signal Diode between the + and - on the analog meter or a resistor of some value to stop the meter from being 0 or 10 any idea on that?
Some would say your ears but being a 1 tone only detector I need a meter that works.
Other mods I am doing are as follows.
1) Hacking the 6 X AA battery holder and connection to the circuit to hold just 1 X 9V battery instead as 1 x 9V battery is a hell of alot easier to install than reading a silly battery cover cap to see the way 6 X AA batteries should be installed.
2) Adding a plug the the circuit board and incorporating a 5 pin CB mic socket on the back of the unit to change out coils as the coil on it is hard wired into the circuit.
3) Moving the 3.5 headphone socket to the front of the unit and the hole for the old one in the back of the unit will be opened up for the above number 2.
Any advice on if this is a BFO or VLF would be grand or any advice on how to make the meter work properly either by a Resistor, Capacitor or Diode on the + and - leads of the meter.
I do intend on building a Chance PI as soon as funds permit so in the mean time I am stuck with this toy.
OK I purchased a very cheap metal detector for £22 off ebay that is made by Maplin and is a Maplin L45BH the £22 I paid is a lot cheaper than the maplin price and for a cheapo detector is quite good with good depth and not to bad discrimination.
Anyway I was unpleased with a few things on it so I am trying to modify it a bit.
The first thing I did was to add some white paint to the position recesses of the Volume/Sensitivity and Discrimination knobs as in direct sunlight it was hard the see where you had them set as the resses was the same color as the knob BLACK.
The second thing I wanted to try and modify was the analogue meter as it was either always 0 or 10, in other words it would be 0 when nothing is detected and then 10 when you detect something, now correct me if I am wrong but to me a meter is supposed to go up in stages according to the depth of the item so an item at 1" would be 10 whereas an item at 15" would be about 0-1. This is where the screw drivers came out and I took it all to bits and on the circuit board are 2 Variable resistors, so I thought this must have something to do with setting the meter so I turned them a little bit and guess what there was no change in the meter but now it hardly detects any copper the copper needs to be 1mm before it detects it so I need to back those off again or increase them.
Anyway my main concern at the moment is to get this meter working properly but I am lost as to what kind of detector this is out of either a BFO or VLF I know it is not a PI as it only has one tone.
While I have it in bits on the table I decided to research the numbers from the SMD chips on the circuit as the circuit is 90% SMD components it has a total of 5 SMD chips, 2 are LM339 Quad Differential Comparators, 2 are GZL1403 or 064C Low Power JFet OppAmps and the other is a HEF405381 or 5381 Triple 2-Channel Multiplexer/Deplexor but I have no Idea from the above componets used what kind it is is it BFO or VLF?
Any help on the kind of detector it is from the above used components would be great as then I will know what I am working with.
I was thinking about a Small Signal Diode between the + and - on the analog meter or a resistor of some value to stop the meter from being 0 or 10 any idea on that?
Some would say your ears but being a 1 tone only detector I need a meter that works.
Other mods I am doing are as follows.
1) Hacking the 6 X AA battery holder and connection to the circuit to hold just 1 X 9V battery instead as 1 x 9V battery is a hell of alot easier to install than reading a silly battery cover cap to see the way 6 X AA batteries should be installed.
2) Adding a plug the the circuit board and incorporating a 5 pin CB mic socket on the back of the unit to change out coils as the coil on it is hard wired into the circuit.
3) Moving the 3.5 headphone socket to the front of the unit and the hole for the old one in the back of the unit will be opened up for the above number 2.
Any advice on if this is a BFO or VLF would be grand or any advice on how to make the meter work properly either by a Resistor, Capacitor or Diode on the + and - leads of the meter.
I do intend on building a Chance PI as soon as funds permit so in the mean time I am stuck with this toy.
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