Metal Detector Kit
Metal Detectors are used for more than hunting for buried treasure on some tropical beach. In the food industry metal detectors are used to detect foreign metal and parts of the machinery in the food. In security they are used to detect weapons. In production equipment they are used for position detection and counting parts. You can even use them for game entertainment or a proximity switch on a toy train set.
This is a kit I got off of Ebay just for the fun of building. While testing it I found some of the results interesting.
Metal Detector Specks
Operating Voltage DC 3-5V
Operating Current 40mA
Standby Current 5mA
Detection Distance 60mm
Alarm mode Sound/Light
PCB Size 86*61mm
Step 1: Tools
Circuit Board Holder
Needle Nose Plyers
Spring Loaded Tweezers
Small Standard Screwdriver
Step 2: Component List
1. Metal Film Resistor R3 470ohm
1. Metal Film Resistor R2 2K
1. Metal Film Resistor R1 200K
1. Potentiometer VR1 100R
2. Ceramic Capacitor C2,C3 0.022uf
2. Ceramic Capacitor C1,C4 0.1uf
1. Electrolytic Capacitor C5 100uf
1. Red LED LED1 5mm
1. S9012 Q2.Q3 TO-92
1. S9018 Q1 TO-92
1. Power Switch SW1 6*5mm
1. Buzzer SP1 9*12mm
1. Power Socket J1 KF301-2P
1. PCB MDS-60
The power switch was missing from the kit but since I had a compatible one in my stores this didn’t slow me down.
This kit did not come with a battery pack; and since this metal detector runs on 3 to 5 volts, I suggest you use a 3 battery holder so if you use 1.2 volt rechargeable batteries for 3.6 volts, or 1.5 volt alkaline batteries for 4.5 volts both give you the voltage you need.
Step 3: Schematic
Although the component placement is obvious on the printed circuit board, and there were no assembly instructions, I reverse engineered a schematic just for those that like them.
Step 4: Assembly
I like to check my parts with a component tester first, it is no use assembling the circuit board with parts that don’t work.
I started at one side holding the components in place with spring tweezers.
Then I soldered the component in place.
This printed circuit board is small; so if there is excess lead, cut the excess off before going to the next part. This will prevent the leads of the previous part from interfering with soldering the next part.
Continue testing and attaching components until the circuit board is assembled.
Step 5: Calibrating the Metal Detector
Remove the tab on the face of the buzzer and attach the battery holder.
Making sure you are nowhere near metal; turn the metal detector on, the LED, (Red Arrow) and the buzzer, (Blue Arrow) may or may not come on.
If the LED and the buzzer do come on adjust the 100 Ω pot, (Yellow Arrow) just enough to turn them off.
If the LED and the buzzer don’t come on; adjust the 100 Ω pot until the LED and buzzer do come on, then adjust the pot the other way just enough to turn them off.
The LED and the buzzer should come on at the same time.
Step 6: Testing
This metal detector is weak; however I tested the detector on a variety of metals and other objects and these were the results.
Gold, Detector Weak Response
Silver, Detector Weak Response
Copper, Detector Weak Response
Lead, Detector Weak Response
Bismuth, Detector Strong Response
Brass, Detector Weak Response
Nickle, Detector Strong Response
Steel, Detector Strong Response
Cast Iron, Detector Strong Response
Aluminum, Detector Weak Response
Neodymium magnet, Detector Weak Response
Ceramic magnet, Detector No Response
Iron magnet, Detector Weak Response
Toroid core, Detector No Response
Transformer core, Detector No Response
Graphite Mold, Detector Strong Response
Oddly enough I thought I would get stronger responses from the magnets because of the magnetic fields effect on the pickup coil. I also expected a stronger response from the powdered iron cores like the toroid or the transformer core. Most of all, the graphite mold gave a strong reaction and it has no metal in it.