Schmitt Trigger SMD Instructions

Schmitt Trigger SMD Instructions

Table of Contents

Introduction

What is the Schmitt Trigger SMD Trainer?

The Schmitt Trigger SMD Trainer kit lets you build a fully adjustable Schmitt trigger, including the hysteresis point and the size of the hysteresis. The Schmitt trigger itself, U1A, is actually configured as an inverting Schmitt trigger such that a signal going beyond the upper threshold will actually result in a low output. The on-board LED indicates the output of this Schmitt trigger, so the LED is also inverting. The output of the module, however, has an extra inverter, so that you an choose between a non-inverting and inverting Schmitt trigger.

Use this kit to test out your soldering skills!

What can you do with the Schmitt Trigger SMD Trainer?

Besides the obvious use of SMD training, the Schmitt Trigger SMD Trainer can be used for any application where hysteresis is needed. For example, a heating control in a room requires hysteresis, otherwise, tiny fluctuations in the ambient temperature could result in the heating rapidly being switched on and off. This rapid switching can damage equipment, and as such, a Schmitt trigger can prevent this by only changing the output after some margin has been passed.

Another excellent use for Schmitt triggers is in RC oscillators. If the input to the Schmitt trigger is connected to a capacitor, and a feedback resistor from the inverting output is connected to the input, then the hysteresis results in a perfect square wave oscillation, whose frequency is dependent on the resistor and capacitor size (such that larger values result in a slower oscillator).

Schematic

Component List

ComponentPCB ReferenceQuantityLooks Like
LM358U11
0805 100R ResistorR11
0805 1K ResistorR21
0805 10K ResistorR3, R42
0805 100nF CapacitorC11
100K PotentiometerRV1, RV22
0805 Red LEDD21
1N5817 DiodeD11
MMBT3904 BJT NPNQ11
Red WireVCC1
Green WireVIN1
Blue WireOUT1
Black WireGND2

PCB

Construction Tips

3D Printable Jig

To help keep the board stable when soldering, you can download a free STL model of a basic jig that can be 3D printed with all common 3D printers. Watch out for the mounting hole pins as they may be vulnerable to snapping if using a low infill density, low wall thickness, or thick layer heights. Additionally, do not use hot air to solder the PCB when using the jig as you will melt the jig.

Model Coming Soon

SMD Construction Guide

To learn more about how to solder SMD components, read through the MitchElectronics SMD Soldering Guide found in our resources section

SMD Soldering Guide

Component Order

When soldering the Schmitt Trigger, you must pay attention to the following chapters in the SMD soldering guide (which can be seen here). You should also solder the components in the order shown below.

  • Integrated Circuits
  • Transistors
  • Resistors
  • Capacitors (ceramic)
  • LEDs
  • Diodes
  • Potentiometers
  • Wires