H bridge circuit

An H bridge is a kind of circuit you use to control the direction (and sometimes speed) of an electric motor, using only a single polarity voltage (you need to reverse the way current flows in order to reverse the way the motor rolls).

How it works:

You have 4 transistors, wired as ON OFF switches. Two signal lines allow you to run the motor in one direction, when reversed, the motor runs in the other direction. It's very straightforward to use and build, but be careful to use only small motors, as the currents drawn from the bigger types can burn your components.

There are 3 modes of operation:
Both equal ( on or off ): motor doesn't run, as it's shorted or not connected
S1 on, S2 off: motor runs in reverse ( from negative [blue] to positive [red] )
S1 off, S2 on: motor runs normal.

Also note, unless you use power transistors, you need to connect diodes across the transistors in order to protect from overvoltages.

Simplified schematic:

Tone generator circuit

Simple, low component count tone generator. It can be adapted to create a morse code circuit, by adding a switch to the output.

How it works:

This circuit is based around the 555 timer circuit, used as an astable (free running) oscillator. The frequency (pitch) of the tone is set by the resistors and capacitors in the left side of the circuit. The first one is a potentiometer (variable resistor), this is our pitch control, which is basically all the external components you need. The capacitor to the far left is to reduce as much noise or undesired operation of the potentiometer, getting a smooth pitch change when adjusting.

You can find the timer's datasheet by following the link: 555 timer

Simple power supply

This circuit is very useful in beginners circuits, since most will work on 5v, which is the voltage of this easy little circuit.

How it works:

This circuit is just an implementation of the 7805 integrated voltage regulator. What this little component does is to lower a voltage and stabilize it by reducing noise and ripple, in order for circuits to have the constant voltage needed to work correctly

You can find the datasheet by following the link: 7805, take note of the typical applications notes, you can find some more uses for this versatile little regulator

Led Chaser

This Led chaser is built using some very common digital logic circuits. Easy to build, easy to work with, and looks amazing in the dark. This circuit will light each led in sequence, creating a moving light illusion.

How it works:

From left to right, the first IC is a binary counter, 74ls163, that is used to generate the address numbers we are going to use in the second part of the circuit, the demultiplexer 74ls138. This demux is the core of the circuit, as this IC pulls low the pin selected in the address inputs. Note that you need an external clock for the counter to work (count).

This is a very simple circuit to build, just take note of the control pins on each IC, since both have enable inputs for counting or output, but once set you don't need to worry about them. It can also be extended to 16 leds by using the Q3 output of the counter to control the enable inputs of a second demultiplexer, or just add a second one to generate a double pattern.

You can find the datasheets for both IC's by following the links: 74ls138 | | 74ls163