Turn the classic 555 timer into an OR logic gate (or should be a NAND Gate) using just a few components! Ideal for quick prototyping, learning, or DIY electronics projects. Take a look at the link bellow to better understand what exactly is this circuit.
http://labdeeletronica.com.br/en/eletronicaanalogica/porta-logica-or-com-ci-555/

IMPORTANT: You will better understand the motivation behind the creation of this circuit by accessing the URL above.

​

 

For what purpose does this Circuit need the 555 Chip ?
.
.
.

 

For what purpose does this Circuit need the 555 Chip ?
.
.
.

This is just to show, in an educational context, that the 555 IC can be used for much more than its common monostable, bistable, or astable configurations. In fact, it's possible to simulate all logic gates using one or multiple 555s, even to the extent of assembling an entire educational computer using several (many) 555 ICs.

 

For what purpose does this Circuit need the 555 Chip ?

It's perfectly possible to simulate the same logic gate without using the 555 IC, but studying how things happen internally within the IC to produce the OR logic gate behavior is an interesting exercise.

 

Appears to me if either button is pressed the output goes high but only as long as the switch is pressed.
Is that the purpose?

 

Welcome to AAC!

Turn the classic 555 timer into an OR logic gate

Technically you've shown a NOR NAND gate. In a poorly drawn schematic.

 

Appears to me if either button is pressed the output goes high but only as long as the switch is pressed.
Is that the purpose?

The circuit correctly matches the truth table of the OR logic gate:

A | B | Output
0 | 0 | 0
0 | 1 | 1
1 | 0 | 1
1 | 1 | 1

You are correct when mentioning that it's necessary to keep the buttons pressed.

 

Welcome to AAC!

Technically you've shown a NOR gate. In a poorly drawn schematic.

The circuit correctly matches the truth table of the OR logic gate.

 

Not an OR gate but a NOR as mentioned by dl324.
If A and B are 0 the output is 1

 

Not an OR gate.
If A and B are 0 the output is 1

 

Not a OR or NOR but an NAND gate.
EDIT: meant to say nand gate.

 

Looks like a NOR gate.

As demonstrated by the circuit in operation, it functions as an OR gate.

 

Not convinced.
What do you consider a high output on the 555?

 

Not convinced.
What do you consider a high output on the 555?

In this circuit, the logic low level corresponds to "0V," and the logic high level is approximately "3.33V" If it were to be used in a real project—although it was not designed for this purpose, as it is purely educational—these voltage levels should be taken into account. As can be observed, it works well for driving a standard LED. However, if it were used to drive a load requiring a voltage higher than "3.3V," the necessary adjustments would need to be made.

 

As demonstrated by the circuit in operation, it functions as an OR gate.

No.

When both inputs are open (logic high), the output is low, and when you ground either one (or both) of the inputs, the output goes high.
That's a NAND gate function.

 

No.

When both inputs are open (logic high), the output is low, and when you ground either one (or both) of the inputs, the output goes high.
That's a NAND gate function.

I understand what you mean... You are referencing the supply voltage at the Trigger and Threshold pins. However, consider using the input buttons as a reference. That is, when both are open, the output is zero, and when at least one of them is closed, the output is 3.3V.

Remember, this is just an educational circuit designed to observe the output behavior according to the states of the input switches...considering an open switch as a low logic level and a closed switch as a high logic level.

 

I understand what you are saying, but if you use the term "logic gate" then you must use logic gate conventions.

 

I understand what you are saying, but if you use the term "logic gate" then you must use logic gate conventions.

The "behavior" of logic gates can be achieved even with entirely mechanical systems where there are no voltage levels. In electronic circuits, the voltage levels assigned to low or high logic levels are purely conventions, which, in the case of traditional ICs using TTL and CMOS technology, have been somewhat standardized. However, this does not mean that any circuit exhibiting the behavior of a logic gate must necessarily follow these "standardized" values. It is perfectly possible to assign different values for high and low logic levels, as long as this is clearly specified in the project documentation.

 

this is just an educational circuit designed to observe the output behavior according to the states of the input switches...considering an open switch as a low logic level and a closed switch as a high logic level.

Then you don't need the 555 for that.
It just unnecessarily complicates the demo.
All you need are two switches and an LED or, at most, two switches, a transistor, and an LED.

 

The circuit correctly matches the truth table of the OR logic gate.

NAND