Sound Light Robot

Introduction: Sound Light Robot

In this Instructable you will be making a sound light device. This device turns on the bright LEDs or light bulbs with music. The music input comes from line out or speak output of a HiFi, computer or mobile phone.

You can see the circuit working in the video.


You will need:

- matrix board,

- heat sink,

- NPN power transistor,

- a few NPN BJT general purpose transistors,

- a two PNP BJT general purpose transistors,

- solder,

- soldering iron,

- encasement (you can use a paper cup),

- electric drill (optional),

- heat transfer paste,

- tape,

- 10 ohm power resistor,

- 270 ohm resistor,

- 4.7 kohm resistor,

- 2 Megohm variable resistor,

- two 1 kohm resistors,

- two 10 kohm resistors,

- 100 kohm resistor,

- 470 nF and 100 nF capacitors,

- nut and bolt for the heat sink,

- a few bright LEDs or two 1.5 V light bulbs,

- scissors or screw driver,

- one general purpose diode.

Step 1: Attach the Heat Sink

Drill two holes in the matrix board and attach the heat sink as shown in the photo.

Step 2: Attach the Power Transistor

Attach the PNP power transistor with bolt and heat transfer paste.

Step 3: Build the Circuit

The Rc1b resistor was chosen as 10 kohm instead of 1 kohm to increase the charging time constant. The discharging time constant is a multiplication of capacitor (C1) and resistor (Rb2) value. An alternative would be to use a higher C1 capacitor value but this would mean using an electrolytic capacitor which is not very reliable compared to the pillow or ceramic capacitors.

You can replace the light bulbs with bright LEDs. If a LED consumes 10 mA with 2 V needed power supply the required series Rc4 resistor is (Vs - Vled) / Iled = (3 V - 2 V) / 10 mA = 100 ohms. You can put an additional LED in parallel and reduce the series resistor in half or you can put a few LEDs with 100-ohm resistors in parallel to power transistor.

You only need three general-purpose BJT transistors. However, you have to purchase a few in case you burn them by connecting to the wrong pins. General-purpose transistors are very cheap.

Rc4 only needs to be a power resistor if you are using light bulbs.

The Rb1 resistor controls the brightness of the light bulbs or bright LEDs.

A typical transistor current gain (current gain) Beta (collector current divided by base current) is 100. However, this value could be as low as 20 or as high as 500. The Beta value is influenced by production tolerances and ambient temperature and bias current.

We can now calculate the assumed minimum Beta values of Q2, Q3 and Q4 transistors that will allow full saturation:

Vs - Vbe = 3 V - 0.7 V = 2.3 V

Q2 Beta: Ic2 / Ib2 = ((Vs - Vbe) / Rb3) / ((Vs - Vbe - Vd) / Rb2)

= (2.3 V / 4,700 ohms) / ((2.3 V - 0.7 V) / 100,000 ohms) = 30.585106383

Q3 Beta: Ic3 / Ib3 = ((Vs - Vbe) / Rb4) / ((Vs - Vbe) / Rb3)

= (2.3 V / 220 ohms) / (2.3 V / 4,700 ohms + 3 V / 100,000 ohms) = 20.1296041116

The specified light bulb current is 0.3 A. Therefore:

Q4 Beta: Ic4 / Ib4 = 0.3 A / ((Vs - Vbe) / Rb4) = 0.3 A / (2.3 V / 220 ohms) = 28.6956521739

Thus the transistors will most likely saturate.

Now we calculate the RC low pass power supply filter cut-off frequency:

fl = 1/(2*pi*Rs*Cs) = 1/(2*pi*100*(470*10^-6)) = 3.38627538493 Hz

You can see in the circuit that I did not implement the RC low pass power supply filter. However, you might need this low pass filter if your battery or power source has a high internal resistance. If the circuit still oscillates even with RC filter then try putting higher capacitor values in parallel with Cs1 and Cs2 capacitors to reduce the low pass cut-off frequency.

Calculate the input high pass filter cut-off frequency:

fh = 1/(2*pi*Ri*Ci) = 1/(2*pi*1000*(470*10^-9)) = 338.627538493 Hz

The high pass maximum cut-off frequency should be no more than 20 Hz. To reduce this frequency we can either:

1. Increase the Ri value. However, this will reduce the circuit gain.

2. Increase the Ci value. This is a better option. We can put an additional 470 nF capacitor in parallel with Ci or replace Ci with a 10 uF (10,000 nF) bipolar capacitor. However, this new capacitor is less reliable and will cost more money. Bipolar capacitors are harder to find on electronic components websites.

Step 4: Put the Circuit in a Paper Cup or Box

You can see that the circuit fits in a paper cup.

The light bulbs are attached with sticky tape.

You can make a hole in cup with a screw driver or scissors for the potentiometer.

The lights will be seen through the cup when on.

Step 5: Secure the Wires With Tape

You can use any sticky tape.

Step 6: Attach the Arms and Legs

Use 1 mm metal wire to attach the arms and Legs to the robot.

You are now done.

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