With this simple circuit you will be able to control the speed of a DC fan according to temperature measured by a temp sensor. It’s an ideal add-on for your PC cooling fans to eliminate produced noise. Requested by some correspondents, this simple design allows an accurate speed control of 12V dc fan motors, proportional to temperature.
A n.t.c. Thermistor (R1) is used as temperature sensor, driving two directly coupled complementary transistors wired in a dc feedback circuit.
An optional circuitry was added to remotely monitor fan operation and to allow some sort of rough speed indication by means of the increasing brightness of a LED.
Posted on Monday, April 18, 2011 • Category: Amplifiers
I am a big fan of surround sound. Up until the moment I finished this amp, I was using two two-channel amplifiers to power four speakers. This was very annoying, because it meant I had two volume controls. This invariably meant that the balance between front and rear was off. Added to this, was that the amplifier for the rear speakers was not very good. It produced too much noise, and allowed clicks and pops from the power grid through, to be amplified and heard. I decided I was going to build a four channel power amplifier, and later a pre-amplifier to feed it. You might wonder why I didn't choose to make a five channel one instead. This is because I don't see the use of the center channel. I will probably write an article detailing why, but for now, suffice it to say that four channels is enough for 2 dimensional sound, which is what 5.1 is as well.
Posted on Sunday, April 17, 2011 • Category: FM Transmitters
This small power FM transmitter can transmit more than 1 km in good conditions. The modulation can be made so much with a microphone or audio source. Circuit of power fm transmitter is built around 2n2218 transistor. Transmitter coil is 5 turns of enameled 22 AWG wire, with diameter of 1 cm without nucleus. Look at the capacitors that it should be ceramic. The antenna should possess from 15 to 40 cm. For transmission it ties a receiver of FM (radio) in the proximity to half volume in a free frequency (that there is not any radio operating), with a wood or plastic key, rotate the screw of CV to capture the frequency of the transmitter.
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