This metal detector electronics circuit also detects metal objects and magnets. When the magnet is near the 10 mH coil, a metal detector project can be supported by a power supply that can provide a DC output voltage of 6 volts to 12 V. If the metal is closer to the coil L1, it will produce a change in the oscillation frequency of the output, which will produce sound at 8 ohm speaker.

Parts list :
R : 47K
C : 2.2uF (2) 10uF
L : 10uH
IC : 555
Speaker 8 ohm
Supply voltage 6-12V

This Simple FM circuit does not have a section that determines the frequency. In the following circuit and all that follows, which determines the frequency of operation is called a resonant circuit or tuned circuit and consists of a coil and capacitor.

This Simple Mikro FM 90Mhz circuit does not include this feature.
The transistor turns on via the 47k and it puts a pulse through the 15 turn winding. The magnetic flux from the winding passes through the coil 6 and in turn the transistor base via the 22n capacitor. This pulse is amplified by the transistor and the circuit is kept active.
The frequency is determined by the 6 turn coil. By moving the whole turns, the frequency decreases. The circuit transmits at 90MHz. It has a very poor and consumes 16mA. The coil is wound on a 3 mm drill and uses son of 0.5 mm.

By adjusting the potentiometer P2 to a high pitch, can enter the circuit into oscillation by emitting a continuous whistle.In this case, we must reduce degradation of sound with the potentiometer P1. For installation components, follow closely the diagram layout.

Bell Electronic Parts list :

All resistors are 1/4 watt unless otherwise stated.
R = 68 ohms
R2 = 1 kohm
R3 = 10 Kohm
R4 = 470 ohms
R5 = 82 Kohm
R6 = 22 Kohm
R7 = 270 ohms
R8 = 10 Kohm
R9 = 47 ohms
Pl = 4.7 MohmsA.
P2 = 220 Kohm A.
Cl = 22uF16V elec.
C2 = 1uF16V elec.
C3 = 0.1 uF 100 Vpol.
C4 = 0.047 uF 100 Vpol.
C5 = 0.047 uF 100 Vpol.
C6 = .47 uF 100 Vpol.
IC1,IC2,IC3 = 741
P = Push.
3 IC Supports 8-pin

These integrated circuits operating at 5 V and 9 V battery 6F22 certainly convenient, voltage is reduced and stabilized by a 78L05 regulator. By rotating the trimmer R2 from one end to another, will change the flashing between 0.5to 3 flashes per second.

This electronic flasher circuit can be placed in bags or placed in a belt to put on waist (when cycling,walking, etc..). You will see this safety circuit is highly efficient flashing in the darkness. Moreover, nothing prevents to build a (relatively inexpensive) and set them on someplaces (legs, back, bike, scooter …) to improve visibility.

List of electronic components Led electronic flasher:
R1 …………… 2.2 kOhms
R2 …………… 10 k trimmer
R3 …………… 220 Ω
R4 …………… 220 Ω
C1 …………… 47 uF electrolytic
C2 …………… 47 uF electrolytic
C3 …………… 47 uF electrolytic
DL1 …………. LED
DL2 …………. LED
IC1 ………….. integrated SN74HC132
IC2 ………….. integrated MC78L05
S1 …………… switch
(Unless otherwise noted, all resistors are 1/4 W 5%

The pin 3 (non-inverting) of the operational amplifier IC1 is connected to the junction of the LDR and R1 trimmer. The LDR being connected to + 12 volts and the trimmer to ground, together form a bridge with a variable value. The opposite pin (inverting) of the operational amplifier is connected to the junction of two resistors R2 and R3, R2 being connected to + 12 volts and R3 to ground, together form the fixed bridge. Voltage at the output of operational amplifier is 6 volts. When the LDR is illuminated by light, at pin 3 of IC1, we have a positive voltage is higher than that present at pin 2and therefore the output pin 6 of IC1 is at logic 1 (at + 12 volts).

The resistor R4 therefore can not biasing the transistor which isa PNP, relay remains inactive. When the LDR is placed in the dark, the pin 3 of IC1 has a lesspositive voltage on pin 2. Therefore, the output pin 6 of IC1 is at logic level 0 (ground). The resistor R4 is grounded and the base of transistor TR1 is biased (PNP).  The latter then becomes conductive and the relay placed in the collector is activated. which used to control any load. The trimmer R1 connected in series with the photoresistor used for test the detection sensitivity.

Parts list :
R1 ………. 10 k trimmer
R2 ………. 10 k
R3 ………. 10 k
R4 ………. 1.2 kOhms
R5 ………. 1.2 kOhms
FR1 ……… photoresistor
C1 ………. 100 uF electr olytique
DS1 …….. 1N4007 diode
TR1 ……… 2N3702 PNP
IC1 ……… Integrated uA741
RL1 ……… Relay 12 V 1 R

When the output circuit is high-D2 turns on and when output is low D1 turns on. The rate of flashing will be determined on the component values ​​R1, R2 and C1. When push button S1 is pressed, C1 begins to charge through R1 & R2.

When the voltage across C1 exceeds two-thirds of the supply voltage of the internal bistable Flip Flop. Pin 7 is low and C1 starts discharging.  Pin 7 is low and C1 starts discharging. When the voltage at terminal C1 falls below one-third of the supply voltage resets internal Flip Flop & pin 7 become high.

C1 begins charging. All this will happen, if the IC is in good condition. Depending on the frequency of discharge and charge D1 & D2 will flash. From these observations we can conclude that IC NE555 is damaged or not.

CMOS IC TS555CN timer wired as a square wave generator of about 5Hz. IC1 is doubled using a combination of capacitor C2 and diode D2 to drive the LED. LEDs can use a white super bright LED light. During the day LDR resistance drops to a few K Ohms and inhibit oscillation of the IC. This will make the LED off.

Mini night lighting parts list :

R1, R2 : 1M
R3 : 47K
R4 : LDR ( Light Dependent Resistor)
C1 : 100nF /63V
C2 : 220uF
D1 : LED
D2 : 1N1819

Notes:
Assemble the circuit on a general purpose PCB.
The circuit can be powered by two 1.5V batteries in series.
The IC1 must be CMOS type because other types do not work at low voltage, as 3V.
An optional switch can be added in series with the battery (not shown in circuit) to
provide a manual ON / OFF.

Antenna : We will soldering one meter length of cable at the end of a first round of the loop that is closest to the collector of transistor Q2.

Adjustment : To work properly, we must adjust VR1 so that we have the Q1 collector voltage between 1.5 and 1.9 volts.

Frequency setting : Tune to an FM radio about 95 MHz (in an area where there is no station) after a few meters from the circuit. We then apply a voltage to the transmitter and began to slowly change the settings of C2 until background noise disappears, once this is achieved, we can test the performance of our voice modulation into the microphone. We also try to change the frequency of transmission separately or together the turns of the coil.

The Micro Wireless Spy FM 88-108 coil construction:
N is the number of turns = 5 turns
D: is the coil radius in inches = 0.5 cm
L is the length in inches = 1 cm

This zener tester based on famous 741 operational amplifier. RV1 can be calibrated in volts, so that when LED 1 just lights, the voltage on pins 2 and 3 are nearly equal. Hence, the zener voltage can be read directly from the setting of RV1. The supply need only be as high a value as the zener itself For a more accurate measurement, a precision pot could be added and calibrated.

Zener tester parts  list :
R1 : 4K7
RV1 : 10 K linier variable resistor
Led
IC1 :  LS741

Diode tester parts list :
D1, D2 : HEP R0052
LP1, LP2 : GE 4B lamp
X1 : 120V tp 6.3V, transformer, Lafayette 33P80508