Noise making using 555 timer

Noise making using 555 timer

parts list:-

555 Timer IC
1K ohm - 1/4 Watt resistor
10K ohm - 1/4 Watt resistor
1M ohm - 1/4 Watt resistor
10uF electrolytic capacitor
0.01uF ceramic disc capacitor
Small Speaker
9V battery connector


This circuit is using a 555 timer chip to make noise using a speaker.
What is happening is that the configuration of components and connections on the 555 chip is causing pin 3 to oscillate rapidly between high and low. If you were to graph these oscillations, it would look like a square wave (a wave the alternates between two power levels). This wave then rapidly pulses the speaker, which displaces air at such a high frequency that we hear this as a steady tone of that frequency.
Make sure that the 555 chip is straddling the center of the breadboard, such that none of the pins might get accidentally connected. Aside from that, simply make the connections as specified in the schematic diagram.
Also note the "NC" symbol on the schematic. This stands in for "No Connect," which obviously means nothing connects to that pin in this circuit.
You can read all about 555 chips on this page and see a great selection of additional 555 schematics on this page.
In terms of the speaker, use a small speaker like you might find inside of a musical greeting card. This configuration can't drive a large speaker, the smaller the speaker you can find, the better off that you will be. Most speakers are polarized, so make certain that you have the negative side of the speaker connected to ground (if it requires it).
If you want to take it a step farther, you can create a volume knob by connecting one outer pin of a 100K potentiometer to pin 3, the middle pin to the speaker, and the the remaining outer pin to ground.

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Automatically blinking LED

Automatically blinking LED

Parts List:
2N3904 PNP transistor
2N3906 NPN transistor
47 ohm - 1/4 Watt resistor
1K ohm - 1/4 Watt resistor
470K ohm - 1/4 Watt resistor
10uF electrolytic capacitor
0.01uF ceramic disc capacitor
5mm red LED
3V AA battery holder

Optional:
10K ohm - 1/4 Watt resistor
1M potentiometer

This next schematic may look daunting, but it is actually rather straight-forward. It is using all of the parts that we have just gone over to automatically blink an LED.

Any general purpose NPN or PNP transistors should do for the circuit, but should you want to follow along at home, I am using 293904 (NPN) and 2N3906 (PNP) transistors. I learned their pin layouts by looking up their datasheets. A good source for quickly finding datasheets is Octopart.com. Simply search for the part number and you should find a picture of the part and link to the datasheet.

For instance, from the datasheet for the 2N3904 transistor, I was quickly able to see that pin 1 was the emitter, pin 2 was the base, and pin 3 was the collector.

Aside from the transistors, all of the resistors, capacitors, and LED should be straight-forward to connect. However, there is one tricky bit in the schematic. Notice the half-arch near the transistor. This arch indicates that the capacitor jumps over the trace from the battery and connects to the base of the PNP transistor instead.

Also, when building the circuit, don't forget to keep in mind that the electrolytic capacitors and LED are polarized and will only work in one direction.

After you finish building the circuit and plug in the power, it should blink. If it does not blink, carefully check all of your connections and orientation of all of the parts.

A trick for quickly debugging the circuit is counting components in the schematic versus components on your breadboard. If they don't match, you left something out. You can also do the same counting trick for the number of things that connect to a particular point in the circuit.

Once it is working, try changing the value of 470K resistor. Notice that by increasing the value of this resistor, the LED blinks slower and that by decreasing it, the LED blinks faster.

The reason for this is that the resistor is controlling the rate at which the 10uF capacitor is filling and discharging. This is directly related to the blinking of the LED.

Replace this resistor with a 1M potentiometer that is in series with a 10K resistor. Wire it such that one side of the resistor connects to an outer pin on the potentiometer and the other side connects to the base of the PNP transistor. The center pin of the potentiometer should connect to ground. The rate of blinking now changes when you turn the knob and sweep through the resistance.

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Potentiometers

Potentiometers

Potentiometers are variable resistors. In plain English, they have some sort of knob or slider that you turn or push to change resistance in a circuit. If you have ever used a volume knob on a stereo or a sliding light dimmer, then you have used a potentiometer.

Potentiometers are measured in ohms like resistors, but rather than having color bands, they have their value rating written directly on them (i.e. "1M"). They are also marked with an "A" or a "B, " which indicated the type of response curve it has.

Potentiometers marked with a "B" have a linear response curve. This means that as you turn the knob, the resistance increases evenly (10, 20, 30, 40, 50, etc.). The potentiometers marked with an "A" have a logarithmic response curve. This means that as you turn the knob, the numbers increase logarithmically (1, 10, 100, 10,000 etc.)

Potentiometers have three legs as to create a voltage divider, which is basically two resistors in series. When two resistors are put in series, the point between them is a voltage that is a value somewhere between the source value and ground.

For instance, if you have two 10K resistors in series between power (5V) and ground (0V), the point where these two resistors meet will be half the power supply (2.5V) because both of the resistors have identical values. Assuming this middle point is actually the center pin of a potentiometer, as you turn the knob, the voltage on the middle pin will actually increase towards 5V or decrease toward 0V (depending which direction that you turn it). This is useful for adjusting the intensity of an electrical signal within a circuit (hence its use as a volume knob).

This is represented in a circuit as a resistor with an arrow pointing towards the middle of it.

If you only connect one of the outer pins and the center pin to the circuit, you are only changing the resistance within the circuit and not the voltage level on the middle pin. This too is a useful tool for circuit building because often you just want to change the resistance at a particular point and not create an adjustable voltage divider.

This configuration is often represented in a circuit as a resistor with an arrow coming out of one side and looping back in to point towards the middle.

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