Posts Tagged ‘BC109’

AM Transmitter by BC109

The circuit is in two halfs, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. The tank circuit L1 and VC1 is tunable from about 500kHz to 1600KHz. These components can be used from an old MW radio, if available. Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit. The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, 100pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted. Oscillation frequency is adjusted with VC1.
Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realising full gain of this stage. The microphone is an electret condenser mic and the amount of AM modulation is adjusted with the 4.7k preset resistor P1.
An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range.

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Control sound automatic by BC109

This circuit is the sound controls automatic circuit, by it will fix to don’t give popularity level in the sound doesn’t expire. When feed sound signal reaches in this circuit , as a result , will have a signal, will the power goes up to flow through LED shine to LDR. The connection and a resister have a side input ,make control popularity level in the sound that a side output get , when see the circuit has already. I uses important equipment , be the transistor number BC109 and other equipment a little again. By you can fix signal sound level can control with VR1 with try fine can decorate follow want.

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Audio Perimeter Monitor by BC109

Notes:
Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for
example, at the bottom of a garden or garage, and used to detect all sound in that area. The cable can
be buried in a hosepipe or duct and is concealed out of sight. The mic is an ordinary dynamic mic insert
and should be housed in a waterproof enclosure with the rest of the circuit.

The mic output is amplified by the two transistors, the output is fed down the cable via the 220u capacitor.
Here, it has a dual purpose of preventing the DC supply from upsetting the bias of the circuit, and also
allowing the smaller ac audio output to pass down the line. At the power supply, the audio is recovered
by the 10k preset and 220u capacitor. It is used to feed a small audio amplifier (such as the 2watt design)
shown earlier on this site.

Source :: http://www.zen22142.zen.co.uk/Circuits/Misc/perim.htm