7400 Series Guide: 74HC14/74LS14 (Hex Schmitt-trigger inverters)

The 74×14 (ex 74HC14) is a common logic IC with six Schmitt-trigger inverters. I love this chip because you can do a lot of cool stuff with it (oscillators, sound, blinking, etc).

In this guide, I will show you everything you need to know about this chip so that you’ll be prepared to build your own projects based on this chip.

74HC14 chip and pinout

What does the 74HC14 / 74LS14 do?

The 74×14 gives you six NOT gates that you can use individually. A NOT gate (or inverter) is a logic gate that outputs the opposite of the input. In the truth table below, you can see what the output will be for any given input:

NOT gate truth table
Truth table for the NOT gate (inverter)

The gates have Schmitt trigger inputs, which means that the threshold voltage for going from a HIGH to a LOW input is different from the threshold for going from LOW to HIGH. Because of this, it’s possible to design an oscillator by just adding a resistor and a capacitor to the gate.

You can see an example of this in the Circuit Example section further down.

How To Use This Chip

The 74HC14 comes in a 14-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One of the differences between the HC and LS chips is that the 74HC14 supports 2V to 6V, while the 74LS14 only supports 5V.

There’s also a 74C14 version that supports up to 15V (and 15 mA of current), but it’s not that easy to find anymore.

To use any of the six Schmitt-trigger inverters inside, just power on the chip by connecting the VCC pin to 5V and the GND pin to 0V (or minus).

7400 series IC connected to 5V on a breadboard

74×14 Pinout

The 74×14 has 14 pins and contains six Schmitt-trigger NOT-gates laid out as shown in the pinout diagram below:

Pin #TypeDescription
1InputInput to the first NOT gate.
2OutputOutput from the first NOT gate.
3InputInput to the second NOT gate.
4OutputOutput from the second NOT gate.
5InputInput to the third NOT gate.
6OutputOutput from the third NOT gate.
7PowerConnect to ground (GND).
8OutputOutput from the fourth NOT gate.
9InputInput to the fourth NOT gate.
10OutputOutput from the fifth NOT gate.
11InputInput to the fifth NOT gate.
12OutputOutput from the sixth NOT gate.
13InputInput to the sixth NOT gate.
14PowerPositive power supply (VCC). Connect to +5V power.
Pin overview for the 74×14 IC

74HC14 Example Circuit – Blinking an LED

In this example, you’ll build an oscillator that blinks an LED at a rate of about 1 time per second. This is one of the simplest oscillators to build, and you can easily use it for other stuff like creating sound.

Blinking LED circuit diagram

You’ll need the following components to build this circuit:

  • 2-6V Voltage Source
  • Schmitt Trigger Inverter (74HC14)
  • Capacitor of 100 µF (C1)
  • 2 x Resistor of 10 kΩ (R1 and R2)
  • A Light-Emitting Diode (LED)

I’ve written a guide on how to build this circuit over at this page, if you want step-by-step instructions on how to build this.

Alternatives and Equivalents for 74HC14 / 74LS14

There are several versions of the 74×14 chip out there. They all do the same thing but have different specifications. This could mean differences in the voltages they support or the maximum current they can provide.

Here’s a list of the most common versions of this chip:

  • 74C14 (CMOS, similar to the 4000-series)
  • 74HC14 (High-speed CMOS)
  • 74HCT14 (High-speed CMOS, TTL compatible)
  • 74LS14 (High-speed TTL)
  • 74LVC14 (Low Voltage TTL)
  • 74AC14 (Advanced CMOS)
  • 74ALS14 (Advanced Low-Power Schottky TTL)
  • 74F14 (Very High Speed)

Note that some manufacturers also add a prefix, such as the SN74HC14 and SN74LS14 by Texas Instruments. There is also a 54 series which you can use in the same way.

Can’t find the 74×14 anywhere? Then try one of the following IC alternatives:

  • 74×04 – Hex NOT gate
  • 74×05 – Hex NOT gate (with open-collector outputs).
  • CD40106 – Hex Schmitt-trigger NOT gate

If you can’t find the 74×14 IC (Integrated Circuit) in your nearby electronics store, no need to worry! You can probably locate it in one of the online stores listed on this page. These stores offer various components and tools for all your electronics projects.

Datasheets for the 74LS14 and 74HC14 chips

2 thoughts on “7400 Series Guide: 74HC14/74LS14 (Hex Schmitt-trigger inverters)”

  1. In the table above showing the input and output of pins 8-13 are labeled incorrectly compared to what it shows in the diagram above

    Reply

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