Projects

 

 

Metal Detector

It's a simple metal detector design that has the quite good characteristics. the principle of operation which one differs from the classic schemes (BFO, transmit-receive known as "two-boxes" metal detector, inductive).

The dynamic mode is used to find targets in interference environment. There is known from theory of signal filtration that if signal shape is determined we can construct optimal filter - the best one for extracting the signal with maximum signal/noise ratio. This filter is known as optimal matched filter. In our device we realized digital optimal matched filter as part of microcontroller software. The filter parameters are optimized for effective ferro- and non-ferro targets detection on 0.5-1.0 m/s velocity of sensor.

Features of the Metal Detector:
Power supply .............................4.5-6V;
DC consumption .......................15 mA;
Indication ...................................sound + 8 LEDs;
Modes ........................................static or dynamic;
Discrimination.............................ferro/non-ferro.


Metal Detector Schematic

Switches controlled (versions V1.9 and V2.0 of firmware):
S0: reset device;
S1: reserved;
S2: on - threshold high, off - threshold low;
S3: measuring time on - 30ms, off - 120ms;
S4: self tuning on/off (in dynamic mode only);
S5: mode on - static, off - dynamic.



Metal detector PCB Layout

Metal Detector Coil Design

Approx. 100 curls 200 mm in diameter. Copper wire in isolation 0,35 mm diameter

 

Mobile phone call indicator

Purpose
This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated. This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashing LED.

The device must be placed a few centimeters from the cellular phone, so its sensor coil L1 can detect the field emitted by the phone receiver during an incoming call.

Device operation

When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

The signal detected by the sensor coil is amplified by transistor Q1 and drives the monostable input pin of IC1. The IC's output voltage is doubled by C2 & D2 in order to drive the high-efficiency ultra-bright LED at a suitable peak-voltage.

Note:

• Stand-by current drawing is less than 200µA, therefore a power on/off switch is unnecessary.
• Sensitivity of this circuit depends on the sensor coil type.
• L1 can be made by winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Remove the coil from the former and wind it with insulating tape, thus obtaining a stand-alone coil.
• A commercial 10mH miniature inductor, usually sold in the form of a tiny rectangular plastic box, can be used satisfactorily but with lower sensitivity.
• IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less.
• Any Schottky-barrier type diode can be used in place of the 1N5819: the BAT46 type is a very good choice.