Monday, September 25, 2023

Automatic Dispenser Using 555 Timer

By Santiago Echeverry Serna

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The 555 timer has been a popular choice in electronics for a long time due to its versatility and wide range of applications.

It can be used as a timer, oscillator, frequency divider, frequency modulator, triangular signal generator, and more.

You can check the Interesting 555 Timer Projects.

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The 555 timer has three main modes: monostable, astable, and bistable.

In this article, we will explore a new mode of operation for the 555 timer that generates a unique pulse when the circuit is powered on.

Unique Mode of Operation for the 555 Timer

The only way to generate another pulse is by turning off the circuit and then powering it on again. While one might think that this can be achieved with the monostable mode by setting pin 2 to low (ground), doing so would result in the output of the 555 timer always being on.

(You can try this yourself)

In this particular monostable mode, pins 5 and 7 are not used. Fig. 1 illustrates the circuit diagram of this specific monostable circuit.

Unique Mode of Operation for the 555 Timer
Fig. 1: The specific monostable circuit

This new configuration of the LM555 timer in monostable mode can be used in various applications, such as alarm systems in cars, turning on a computer in a car, and creating an automatic dispenser for soap or antibacterial gel.

How does this Unique Mode Work?

To explain the operation of this new mode, let’s refer to Fig. 1. When the circuit is powered on, capacitor C initially has no voltage, resulting in both pin 6 and pin 2 of the 555 timer having a voltage of zero.

In the reset comparator, the inverse input of the comparator has a voltage of (2/3)VCC, while the non-inverse input has a voltage of zero. As a result, the internal comparator output is low.

Now, let’s consider the set comparator. At this time, the inverse input is at 0V, and the non-inverse input is at (1/3)VCC. Consequently, the comparator output will be high.

In conclusion, when the capacitor has some voltage, the output of the 555 timer will be high.

While the capacitor is charging, the circuit continues with its output in the high state. The output of the 555 timer goes low only when the voltage in the reset comparator exceeds (2/3)VCC.

When the output of the 555 timer is low, the capacitor cannot discharge through pin 7 since this pin is not used in this configuration. Thus, the 555 timer cannot generate additional pulses.

Therefore, the only way to generate a new pulse is to turn off the circuit and then turn it on again.

Automatic Dispenser Using LM555

Many people have attempted to create automatic dispensers using an Arduino with an infrared module, while others have used just the module itself.

However, using an Arduino Nano for this purpose can be more expensive than using a 555 timer. Some dispensers do not require a microcontroller or an Arduino; they work directly.

If you put your hand near the dispenser and keep it there, the dispenser will dispense soap or gel until you remove your hand, potentially resulting in excess usage.

A commercial automatic dispenser dispenses soap or gel for a specific amount of time. Even if you trigger the sensor multiple times, the dispenser waits until you remove your hand from the sensor before allowing you to dispense again.

Circuit and Working


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