Build These Simple 555 Circuits
Simple 555 timer circuit: As shown in the figure the IC 555 is configured as a monostable mutivibrator. On pressing the switch S1, a momentary logic high appears at pin 2 of the IC and its output at pin 3 goes high switching ON the relay and the load connected to the relay contacts. The output will sustain the position till its timing capacitor C1 gets fully discharged through the variable resistor VR1. The value of this resistor may be varied to get the desirable time delays. The delay may be calculated using the below given formula:
T = 1.1 × (VR1 + R1) × C1
Simple voltage monitor: Another important use of IC 555 in the monostable mode is in the form of a voltage monitor. Here the voltage to be monitored can be set by the preset P1. For example if it is required to monitor a voltage level of 9, the preset may be adjusted accordingly. Now if voltage at pin 2 falls below 9 volts, the output will immediately go high giving a visual or an audible indication or can switch ON a relay to implement the desired safety measure. Similarly it can be used to monitor and sense a high voltage exceeding the set level.
Simple 555 electrical pulse generator: Referring to the circuit diagram we can see that in an astable mode the IC oscillates continuously to produce a string of electrical pulses. These pulses are normally in the form of a square wave. Here no external trigger is required and the circuit starts to oscillate immediately on receiving the supply voltage. Its frequency can be altered by changing the value of either the capacitor C1 or the POT VR1. By sufficiently lowering the frequency and by connecting an LED at its output pin, the circuit may be used as a simple 555 led flasher. By increasing the frequency to a relatively higher level, the circuit may be used to drive a speaker or a buzzer to produce an audio tone.
The above mentioned 555 circuits are quite simple in design; hopefully you will enjoy building these circuits and see them actually working. If you need any help feel free to add a comment (comments need moderation, and may take time to appear).
Pin-out Image Credit: http://pfnicholls.com/electronics/555_pinout.png