Friday, April 20, 2012

Gold Detector Schematic

Gold Detector Schematic circuit diagram

Here the very simple and easy build gold detector circuit. The circuit capable to sense gold or metal or coins from a distance of about 20cm, depending on the size of the object to detect.

The circuit oscillates at about 140kHz and a harmonic of this frequency is detected by an AM radio. You can simply tune the radio receiver until a squeal is detected.

When the search coil is placed near a metal object, the frequency of the circuit will change and this will be heard from the speaker of AM radio.

Below image is the construction of the circuit, you will see that the radio is placed on the hand stick of the complete detector.

gold detector construction

gold detector coil

ReadMore[..]

Sunday, April 15, 2012

12 Volt DC Fan Temperature Control

12 Volt DC Fan Temperature ControlHere is a simple circuit based on two transistors that can be acclimated to ascendancy the acceleration of a 12 V DC fan depending on the temperature.A thermistor (R1) is acclimated to faculty the temperature. When the temperature increases the abject accepted of Q1 (BC 547) increases which in about-face decreases the beneficiary voltage of the aforementioned transistor. Since the beneficiary of Q1 is accompanying to the abject of Q2 (BD 140), the abatement in beneficiary voltage of Q1 advanced biases the Q2 added and so do the acceleration of the motor. Also, the accuracy of the LED will be proportional to the acceleration of the motor.

Notes.

  • The R1 can be a 15K @ 20°C ,N.T.C thermistor.
  • The M1 can be a 12V,700mA fan motor.
  • The capacitor C1 must be rated 25V.
  • The circuit can be powered from a 12V PP3 battery or 12V DC power supply.
  • Assemble the circuit on a good quality PCB or common board.
ReadMore[..]

Sunday, April 1, 2012

Simple Intercom Circuit with Transistors

Simple Intercom Circuit with Transistor

This is a 2-station simple intercom circuit build based on transistors part and using common 8R mini speakers. The speaker works as microphone and generate sound, so there is no need microphone for this intercom. The "press-to-talk" switches should have a spring-return so the intercom can never be left ON, push on switch can be used for this kind of task.



The secret to preventing instability (motor-boating) with a high gain circuit like this is to power the speaker from a separate power supply! You can connect an extra station (or two extra stations) to this circuit design.

Build the circuit into two separated boxes (for 2 stations). On each box should be use 2 ports for external power supply port (if you use external power supply, not battery) and connection port to other stations. Create some holes for speaker push on switch.
ReadMore[..]