How to make Pulse stretcher with MOSFET – DIY

Are you looking for a simple yet effective way to stretch short electrical pulses into longer ones? A Pulse Stretcher Circuit is the perfect solution, and in this guide, we’ll show you how to build one using a 2N7000 MOSFET . This DIY project is ideal for hobbyists, engineers, and electronics enthusiasts who want to experiment with pulse generation and signal conditioning. Let’s dive in!

What is a Pulse Stretcher?

A Pulse Stretcher Circuit is designed to extend the duration of an input pulse while maintaining its original characteristics. It’s commonly used in applications like signal processing, timing circuits, and digital systems. In this project, we’ll use a 2N7000 MOSFET as the core component to create a reliable pulse stretcher.

Components Required

To build this circuit, you’ll need the following components:

1. Input Circuit:

   • Momentary push button
   • 2N3904 transistor (Q3)
   • Resistors: R5 and R6 (biasing resistors)

2. Pulse Stretcher Circuit:

   • Two 2N7000 MOSFET transistors
   • Resistors: R2, R3
   • Capacitor: C1 (determines the output pulse duration)

3. Output Circuit:

   • Schmitt trigger circuit (for clean output signals)

You can easily find these components at your local electronics store or online. For more advanced projects, check out our guide on how to build a pulse generator circuit .

Circuit Design and Working Principle

Input Circuit

The input circuit consists of a momentary push button and a 2N3904 transistor (Q3) along with biasing resistors R5 and R6. When the switch is pressed, it grounds the circuit, creating a short pulse that triggers the next stage.

Pulse Stretcher Circuit

This is the heart of the design, featuring two 2N7000 MOSFETs , resistors R2 and R3, and capacitor C1. Here’s how it works:

• The capacitor C1 determines the output pulse duration. You can calculate the required capacitor value using our online time constant calculator .
• When a short positive pulse drives MOSFET Q1, it discharges capacitor C1, causing the output to go high (+5V in this case).
• As C1 charges up to the switching threshold of the output inverter (a Schmitt trigger or another nMOS transistor), the output returns to zero.

Output Circuit

The output circuit uses a Schmitt trigger to ensure a clean and stable output signal. For more details on Schmitt triggers, read our article on inverting and non-inverting Schmitt triggers .

Key Features of the Circuit

1. Adjustable Pulse Duration: By changing the value of capacitor C1, you can control the stretched pulse duration.
2. Compact Design: The use of MOSFETs ensures minimal power consumption and a small footprint.
3. Versatile Applications: This circuit can be integrated into various systems, including timing circuits, oscillators, and signal conditioning modules.

For inspiration on related projects, explore our guides on astable multivibrators using transistors and simulating a 555 timer as a monostable multivibrator .

Step-by-Step Instructions

1. Assemble the Input Circuit:

   • Connect the momentary push button and configure the 2N3904 transistor with resistors R5 and R6 to generate a short pulse when the button is pressed.

2. Build the Pulse Stretcher:

   • Use two 2N7000 MOSFETs, resistors R2 and R3, and capacitor C1. Ensure proper connections to achieve the desired pulse stretching effect.

3. Set Up the Output Circuit:

   • Add a Schmitt trigger to clean up the output signal. This step ensures that the stretched pulse is free from noise and distortion.

4. Test the Circuit:

   • Power up the circuit and press the push button. Observe the stretched pulse on an oscilloscope or multimeter.
    

One way to test the circuit is via simulation before actually building it. Below video shows how the pulse stretcher circuit designed with MOSFET works.