Wednesday, July 9, 2014

Make a Simple FM Transmitter

This circuit uses a small microphone to capture the sound and some transistors to generate radio waves that can be picked up by a FM receiver like a car stereo.

How it works:

From left to right, the first part is the microphone and some resistors to get it working. Next we have a capacitor and the first transistor, this amplifies the sound from the microphone so that it can be loud enough to work with. The last part, there is a transistor, a coil and some capacitors. This part generates the radio waves and combines them with the sound from the mic to transmit it thru the antenna.

Make a Simple FM Transmitter

The coil is made with about 9 turns of wire, use a pencil to get the right diameter for the coil. The capacitor with the arrow is called a trimmer capacitor, it has a small screw to adjust the value, we'll use it to tune a certain frequency or station to transmit on.

simple fm radio transmitter(click to enlarge)

Wednesday, October 30, 2013

TTL square wave generator circuit

Simples Gerador de onda quadrada TTL

Here's a useful circuit, he is a TTL square wave oscillator, it uses three logical ports, and also a capacitor and a resistor to adjust the frequency. The circuit can be used as a Clock Oscillator, standard signal, etc. The oscillator uses a 7400 integrated circuit, the table below shows the values of C * and R * to achieve the desired frequency, which can be chosen between 100 hz and 1 MHz


Tuesday, December 18, 2012

Simples Sound Activated Switch

Circuit Project: Sound Activated Switch circuit

With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. An alternative use is burglar protection — if someone wants to open the door or break something the light will come on, suggesting that someone’s at home. The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used.