This is a step by step instructable showing how to light twelve LED's in different patterns using only two potentiometers (Pots).
It is a very simple and economical project that doesn't require any special skills (except some soldering) but only a very little knowledge about electronics.
Step 1: Requirements
12 x 5mm led's (choose multiple colors)
4 x 100 ohm resistance
4 x 33 kilo-ohm resistance
4 x BC 548 transistor (or any general purpose NPN transistor)
4 x 22uf electrolytic capacitors
2 x 250k pots
1 x 9v Battery
1 x battery clip
1 x On/Off switch
1 x General purpose PCB Board
A few jumpers (to deal with intersections in the circuit)
Step 2: Construction
For making on Bread Board
1. Arrange all the components as shown in the circuit diagram.
2. Make the connections accordingly.
NOTE: I have simplified the connections for led's in the form of a panel. So that if the panel is made separately on pcb then you can easily make this circuit on bread board.
On Genral purpose PCB
1. Properly study the layout image.
2. Place the components at appropriate places.
3. Solder the components at their respective places.
4. Observe carefully the soldering path connections and then do soldering.
(or you can also use wires instead of making the solder paths, a bit easy for those who don't have very good hand at soldering).
5. Connect the Battery at appropriate terminals and see the project work.
Note: You can make different types of led panels according to the given circuit and then connect it to the circuit using a ribbon wire. This is also helpful in case few led's stop working then you can use different panel if already made.
Step 3: How This Works?
The working of this circuit is based on two astable multivibrators. One multivibrator is formed by transistor T1 & T2 while the other one is formed by T3 & T4. The duty cycle can be varied by changing RC time constant, which can be done through the two pots and different LED patterns can be generated.
An astable multivibrator is a regenerative circuit consisting of two amplifying stages connected in a positive feedback loop by two capacitive-resistive coupling networks. The transistors act as the amplifying elements.
The circuit is usually drawn in a symmetric form as a cross-coupled pair. Two output terminals can be defined at the active devices, which will have complimentary states; one will have high voltage while the other has low voltage. The circuit is implemented by by the coupling capacitor that instantly transfer voltage changes because the voltage across a capacitor cannot suddenly change. Hence, in each state one transistor is ON and the other is OFF, thus producing the needed effect to produce the required patterns and making the circuit work.
Step 4: PCB Version
I have also made a PCB version of this project. In this I used led's of three different colors. Watch the video to see it working. The PCB connection layout is attached and the component layout is same as the image in the previous step.