Denki Control Lab Practical PLC and electrical control guides
Circuit Basics

Press-and-Hold Circuit Basics: Output ON Only While the Button Is Pressed

A press-and-hold circuit turns the output ON only while the input button is being pressed. When the button is released, the output returns OFF.

  • Understand the simplest input-to-output ladder behavior.
  • Separate this circuit from self-holding and one-shot circuits.
  • Check the input, output, wiring, and PLC monitor in a calm order.
Start with the overview Jump to field checks

Good for

  • Beginners learning ladder logic from input and output basics.
  • People who want to understand “ON only while pressed”.
  • Field workers checking push buttons, PLC inputs, and outputs.

Not the first topic if

  • You need a circuit that stays ON after releasing the button.
  • You are looking for a one-pulse operation.
  • The machine uses safety circuits or interlocks that must not be simplified.

Main conclusion

  • Input ON means output ON.
  • Input OFF means output OFF.
  • No memory contact is used, so the output does not stay ON.

Quick navigation

Overview Ladder flow Similar circuits Field checks Common mistakes Summary

What is a press-and-hold circuit?

It is a basic circuit where the output follows the input while the button is being pressed.

In a press-and-hold circuit, the output is ON only while the push button input is ON. When the operator releases the button, the input turns OFF and the output also turns OFF.

This is one of the easiest ladder logic patterns to understand because it does not use memory, latch, or self-holding contacts.

Overview of a press-and-hold circuit where the output is on only while the push button is pressed
The output follows the button state. Pressing the button turns the output ON, and releasing it turns the output OFF.
Senior technician character
Senior

This circuit is the basic idea of “input ON equals output ON”. It is useful before learning self-holding or one-shot logic.

Junior technician character
Junior

So if the output stays ON after I release the button, it is probably not this simple press-and-hold circuit.

Basic ladder flow

The ladder is simple: a normally open input contact drives one output coil.

In the simplest form, the ladder rung has a push button input contact on the left and an output coil on the right. When the input condition is true, the output coil turns ON.

Ladder logic flow for a press-and-hold circuit showing input ON output ON and input OFF output OFF
The output does not have a holding contact. It simply follows the push button input.
Button input Ladder condition Output result Field image
Pressed Input contact is ON. Output coil turns ON. The device moves or lamp turns ON only while pressing.
Released Input contact is OFF. Output coil turns OFF. The device stops or lamp turns OFF immediately.

Beginner takeaway

If the input is not ON in the PLC monitor, the output should not turn ON in this basic circuit. Start by checking the input status.

Difference from self-holding and one-shot circuits

This circuit has no memory and no pulse-only behavior.

A press-and-hold circuit is often confused with self-holding and one-shot circuits. They may all use a push button, but the behavior is different.

Circuit type What happens Key difference
Press-and-hold Output is ON only while the button is pressed. No memory contact is used.
Self-holding Output stays ON after the start button is released. A holding contact or latch condition keeps the output ON.
One-shot Output turns ON for only one scan or one short pulse. It reacts to the edge of the input, not the whole pressing time.

Watch the actual behavior

If the output remains ON after the button is released, look for a holding contact, latch instruction, set/reset logic, or another condition keeping it ON.

Field checks when the output does not turn ON

Check the input, PLC monitor, output, wiring, and device side in order.

Field check points for a press-and-hold circuit including input monitor output monitor wiring and device checks
Do not start from the output device only. First confirm whether the PLC input turns ON when the button is pressed.

1. Button input

Press the button and confirm the PLC input monitor turns ON.

2. Ladder condition

Check whether the rung condition becomes true while the button is pressed.

3. Output monitor

Confirm whether the output coil turns ON in the PLC monitor.

4. Output wiring

Check terminal looseness, relay wiring, power supply, and common wiring.

5. Device side

Check the lamp, relay, solenoid, motor starter, or actual load connected to the output.

6. Interlocks

Confirm there are no stop, safety, alarm, or permission conditions blocking operation.

Common mistakes

Many beginner mistakes come from expecting the output to stay ON.

Common mistakes in press-and-hold circuits including confusing it with self-holding and missing input monitor checks
This circuit is intentionally simple. If you need the output to stay ON, use a different circuit pattern.

Expecting memory behavior

A press-and-hold circuit does not keep the output ON after the button is released.

Checking only the output

Always check whether the PLC input turns ON first.

Ignoring common wiring

Input and output common wiring can stop the signal even when the button or load is normal.

Missing interlocks

Even a simple rung may be combined with stop, alarm, or permission conditions in real machines.

Do not bypass safety circuits

If the circuit involves safety doors, emergency stops, two-hand operation, or hazardous motion, do not simplify it as a basic press-and-hold circuit. Follow the machine documentation and site rules.

Summary

A press-and-hold circuit turns the output ON only while the input button is pressed. It is a basic ladder pattern where the output follows the input state.

It is different from a self-holding circuit because it does not keep the output ON. It is also different from a one-shot circuit because it stays ON for the entire time the input is ON.

Final takeaway

Think of this circuit as “button ON = output ON, button OFF = output OFF”. That simple idea helps you read many beginner ladder circuits more calmly.

Read these next to connect press-and-hold operation with PLC basics and motor control devices.

Start/Stop Circuit Basics

Learn the basic start and stop circuit pattern used before more advanced ladder logic.

PLC Basics

Review how PLCs read inputs, execute logic, and drive outputs.

Magnetic Switch Basics

Understand how magnetic contactors switch motors and larger loads from control signals.