HOW YOU CAN USE 555-TIMER TO OPERATE A BULB FOR A GIVEN TIME
HOW YOU CAN USE 555-TIMER TO OPERATE A BULB FOR A GIVEN TIME
How to use 555-Timer IC in a circuit to operate a Bulb (Lamp) to remain ON for minutes, before returning back to its Off state.
Stage 1
555-Timer has vast application in electronics. In my recent post I showed you other forms in which a 555-Timer could be applied. Today, we shall use 555-Timer in a Monostable Multivibrator configuration to trigger a Driver (Transistor) in energizing a relay and in turn operate a lamp of 230V AC when the relay normally open contact is energized.
Above shows a configuration of a 555-Timer connected in a monostable pattern. This is achieved by connecting Pin 6 and Pin 7 together (bridged using a jumper). Then, connect Pin 8 to the supply rail (power supply line). Then, connect a 10kΩ resistor from pin 4 to the supply rail and then, also connect a capacitor (electrolytic capacitor) of 100µF 16v from that same pin 4 to ground (0v or neutral line of the power supply). The essence of the resistor capacitor network at pin 4 is to slow down or stop immediate start up of voltage at pin 4 when the power source is turn On initially. This will eliminate false triggering of the 555-Timer from operating the Lamp when we didn’t even intend for nit to be operated. Now, from pin 7, connect a resistor of 100kΩ variable resistor in series with a 10kΩ fixed resistor to the supply rail (power supply line). That is to say that, the two resistors will be in series and one of its terminals will be connected to pin 7 and the other terminal will be connected to supply rail. The fixed resistor is to ensure that the variable resistor when adjusted to 0Ω will not affect the circuit in anyway. And now, connect a 1000µF 16v capacitor from pin 7 or pin 6 to ground (negative rail or neutral line of the power source).
Lastly in regard to the first stage, connect a resistor of 10kΩ in series with pin 2 (Trigger Pin or Input) and the supply rail. Then, connect a push button soft switch between pin 2 and ground (neutral rail). This is to keep the input to the 555-Timer IC High so as not to make it “floating” to avoid it been falsely triggered.
Stage 2
This is the last stage if I might conclude from my perspective. This is just a transistor driver stage. It is simply a transistor connected to function as a switch. When its Base-Emitter junction is forward bias by the presence of a voltage from the output of the monostable multivibrator (555-Timer), it cause the electrons to migrate from the emitter to the collector thereby causing large amount of a current to flow through the relay thereby energizing the relay and its contact is therefore closed and thus, our lamp been connected in series with the relay-contacts is operated ON. The resistor in series with the Base of the transistor is just to limit the amount of current flow into the Base of the transistor to a safe level not to damage the transistor or exceed its ratings. The relay coil terminal is connected in between the collector of the transistor and the supply rail. Note also, a diode has to be connected across the collector of the transistor and the supply rail. This is to eliminate any back-emf that might be produce by the relay coil when it de-energizes thereby damaging the transistor. Finally, the Lamp (AC Bulb) is then connector in series with the normally-Open contact of the relay and the other terminal goes to the Live connection of the AC Source. Then the other terminal goes to the Neutral Line of the AC Source.
In a nutshell, the relay is just acting in the place of a normal home switch (Lamp Switch).
Thanks for your time. Let’s make it a date tomorrow so we share another electronics idea together. You are special.
Isaac Johnson
