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TI / Nexperia / many · Integrated circuit

74HC14 Hex Schmitt Inverter

Six inverters with hysteresis. The part that turns a mushy signal into a clean edge, debounces a switch with one resistor and one cap, and makes an oscillator out of nothing.

Cheat sheet (SVG)
Logic level
2-6 V (HC)
Package
PDIP-14 / SOIC-14

1.Pinout diagram

Highlight a signalhover to preview, click to keep

Pins 1-7

74HC14

Pins 8-14

Pin detail

Hover a pin for its mappings and gotchas. Click to keep it here.

Logic level
2-6 V (HC)
Package
PDIP-14 / SOIC-14

Fig. 1. 74HC14 Hex Schmitt Inverter, PDIP-14. Hover or tap a signal to light up every pin that carries it.

2.Watch out

  • Roughly 0.9 V of hysteresis at 5 V: the input has to rise past about 2.9 V to flip one way and fall below about 2.0 V to flip back. That gap is the whole point, and it is why a plain 74HC04 cannot do this job.
  • Switch debouncing: switch to ground, 10k pull-up, 100 nF to ground at the input. The cap slews, the hysteresis turns the slew into one clean transition. No code, no timers.
  • Relaxation oscillator: a resistor from output back to input and a cap from input to ground. Frequency is roughly 1 / (0.8 x R x C). One chip gives you six.
  • It also rescues slow edges from long cables, opto-couplers and photodiodes, all of which produce ramps a normal logic input will chatter on.
  • Pin order alternates input then output down the left, and output then input up the right, the same as the 74HC00.
  • The CD40106 is the same function in 4000-series CMOS, which runs to 18 V and is handy when the signal swings above 6 V.

3.Relaxation oscillator

What has to go around the chip before it will run.

VCCGND74HC14100 nF between 1A (1) and GND100 nF100 nF between VCC (14) and GND100 nFGND (7) to GNDVCC (14) to VCC100 kOhm between 1Y (2) and 1A (1)100 kOhm1A 11A 11Y 2GND 7VCC 14VCC 14
Fig. 2. Relaxation oscillator, drawn from Table 1. Crossing wires are not connected.
Table 1. External parts, and why each one is there.
PartBetween
100 kOhm1Y (2) to 1A (1)
100 nF1A (1) to GND
100 nFVCC (14) to GND

Only a Schmitt input does this. The same two parts on a plain 74HC04 produce a sine-ish mess or nothing at all, because there is no hysteresis to snap the transition.

4.Full pin reference

Every pin, alias and mapping. This is the table that prints.

Table 2. Pin assignments.

Complete pin reference for 74HC14 Hex Schmitt Inverter
PinNameFunctions

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