7404 IC Pinout: Hex Inverter Logic Gate Diagram
The 7404 is one of the simplest ICs in the 7400 TTL logic family -- six NOT gates in a single 14-pin DIP package. It inverts a logic signal: HIGH in gives LOW out, LOW in gives HIGH out. Despite its simplicity, it shows up constantly in real circuits as a signal inverter, logic buffer, oscillator building block, and input conditioning circuit.
This guide covers the 14-pin DIP pinout, the truth table, operating characteristics across TTL and CMOS variants, and practical breadboard uses.
The 14-Pin DIP Pinout
The 7404 is a 14-pin dual in-line package (DIP). Pin 1 is identified by a notch or dot at one end of the package.
┌──┬──┐
1A 1 │ ┴ │ 14 VCC
1Y 2 │ │ 13 6A
2A 3 │ │ 12 6Y
2Y 4 │7404 │ 11 5A
3A 5 │ │ 10 5Y
3Y 6 │ │ 9 4A
GND 7 │ │ 8 4Y
└─────┘
Pin 14 = VCC (supply voltage) Pin 7 = GND
Every gate has an input pin (A) and an output pin (Y). Six gates total: 1A/1Y, 2A/2Y, 3A/3Y, 4A/4Y, 5A/5Y, 6A/6Y.
The Most Common Breadboard Mistake
Forgetting to connect VCC and GND. The IC will not work if VCC (pin 14) and GND (pin 7) are not connected even though you have valid logic signals on the input pins. On a breadboard, those two pins commonly sit in the middle of the chip and are easy to overlook.
Truth Table
For each of the six inverter gates:
| Input (A) | Output (Y) |
|---|---|
| 0 (LOW) | 1 (HIGH) |
| 1 (HIGH) | 0 (LOW) |
That is the complete truth table for a NOT gate. No edge cases.
7404 Variants: TTL vs. CMOS
The "74" prefix covers several logic families with different supply voltage and speed characteristics:
| Part Number | Family | VCC Range | Propagation Delay | Output Drive |
|---|---|---|---|---|
| 7404 | Standard TTL | 4.75--5.25V | ~22ns | 16mA sink |
| 74LS04 | Low-Power Schottky | 4.75--5.25V | ~10ns | 8mA sink |
| 74HC04 | High-Speed CMOS | 2--6V | ~7ns at 5V | ±25mA |
| 74HCT04 | CMOS, TTL-compatible inputs | 4.5--5.5V | ~7ns | ±25mA |
| 74AHC04 | Advanced High-Speed CMOS | 2--5.5V | ~3.5ns | ±8mA |
For a 5V Arduino or standard TTL breadboard circuit, the 74HC04 or 74HCT04 are the go-to modern replacements for the original 7404. They are faster, run at lower supply voltages, have better drive strength, and are widely available.
For 3.3V systems (ARM microcontrollers, Raspberry Pi GPIO), use the 74HC04 (which works from 2V) rather than the HCT04 (which requires at least 4.5V supply).
Using the 7404 on a Breadboard
Required Connections First
- Connect pin 14 (VCC) to the positive supply rail (5V for standard TTL/HCT; 3.3V or 5V for HC).
- Connect pin 7 (GND) to the ground rail.
- Add a 0.1µF bypass capacitor between VCC (pin 14) and GND as close to the chip as possible. This is not optional on a working prototype -- without it, the switching transients cause glitches on the supply rail that can corrupt nearby logic.
Inverting a Signal
Connect the signal source to any input pin (1A, 2A, ..., 6A). The inverted output appears on the corresponding Y pin.
Example: Arduino digital output to gate 1:
- Arduino D7 → pin 1 (1A)
- Pin 2 (1Y) → LED anode → 330Ω resistor → GND
The LED is now active-low -- it illuminates when D7 is LOW.
Using Unused Gates
Unused inputs must not be left floating. A floating TTL input acts as a weak logic HIGH, which may cause the output to oscillate and draw extra supply current. Tie unused inputs to GND (for a permanently HIGH output) or to VCC (permanently LOW output). For CMOS variants (74HC04), floating inputs are more serious -- they can latch-up or draw high current. Always tie them.
Building a Simple RC Oscillator
A single inverter gate can form a crude oscillator with one resistor and one capacitor. Wire it as a Schmitt feedback oscillator:
- Connect output (1Y) back to input (1A) through a resistor R (e.g., 10kΩ).
- Connect a capacitor C (e.g., 10nF) from the input (1A) to GND.
Approximate frequency: f ≈ 1 / (1.2 × R × C)
For R = 10kΩ, C = 10nF: f ≈ 1 / (1.2 × 10,000 × 0.00000001) ≈ 8.3 kHz.
Note: this calculation assumes the 74HC04, which has a defined input threshold. The standard 7404 has poorly defined thresholds and is not ideal for this oscillator. Use the 74HC04 or the purpose-built 74HC14 (Schmitt trigger inverter) for a more stable oscillator.
Signal Conditioning: Logic Level Translation (Limited)
The 7404 is occasionally used to condition noisy open-collector or open-drain outputs. A 10kΩ pull-up to VCC on the 7404 input, with the open-collector output pulling it low, gives a clean TTL-level signal at the 7404 output.
It does not do full voltage level translation -- for 3.3V to 5V and vice versa, use a dedicated level shifter (BSS138 MOSFET, TXB0104, or similar).
Driving Outputs
Each gate output can sink 16mA (standard 7404) or source/sink 25mA (74HC04). This is enough to drive a single LED directly with a series resistor (see LED circuit article for resistor sizing). For loads beyond 25mA, buffer the output through a transistor or MOSFET.
The output low voltage (Vol) is typically 0.4V for TTL, 0.1V for CMOS -- close enough to GND for downstream logic.
Common Failure Modes and Troubleshooting
When a 7404 circuit misbehaves, work through the likely causes in order before assuming the chip itself is bad.
| Symptom | Likely Cause | How to Check |
|---|---|---|
| Output stuck HIGH or LOW no matter what the input does | Pin 14 (VCC) or pin 7 (GND) not connected | Measure voltage between pin 14 and pin 7 with a multimeter -- it should read the supply voltage |
| Chip runs noticeably warm and draws more current than expected | An unused input is floating instead of tied to VCC or GND | Probe each unused input pin -- a floating CMOS input often reads an unstable mid-rail voltage instead of a clean HIGH or LOW |
| One gate stopped working while the others on the same chip still function | Localized ESD damage to that gate | Swap the signal to a different unused gate on the same chip to confirm; if it works there, the original gate is damaged |
| A gate worked on the bench but died shortly after handling | Electrostatic discharge during handling, more common on CMOS (74HC04) than TTL (7404/74LS04) | No fix once damaged -- replace the chip and add ESD precautions going forward |
| Output voltage sags and downstream logic misreads it | Output loaded beyond its rated sink/source current | Reduce the number of loads on that output or buffer it through a transistor |
A quick first check on any dead 7404 circuit is simply confirming VCC and GND are present at the chip with a multimeter -- it catches the single most common wiring mistake before you spend time suspecting the silicon.
ESD Handling for CMOS Variants
The original 7404 and the 74LS04 are bipolar TTL parts and are relatively tolerant of static discharge during normal handling. The 74HC04, 74HCT04, and other CMOS variants are not -- their gate inputs are extremely high impedance, and a static discharge from a hand or a synthetic-fiber work surface can punch through the thin oxide layer inside the gate and destroy it instantly, often with no visible sign of damage.
Practical precautions when working with CMOS 74-series parts:
- Store spare chips in anti-static foam or a conductive tube, not loose in a parts drawer.
- Touch a grounded metal surface before handling the chip if you are not using a wrist strap.
- Leave chips in their packaging until the breadboard or PCB is ready for them.
- Avoid inserting or removing CMOS ICs from a circuit while it is powered.
A chip that worked once and then failed permanently after being handled, without any wiring changes, is a classic ESD symptom rather than a design fault.
Driving Multiple Loads: Fanout Considerations
Each 7404 output is rated for a specific sink and source current (16mA sink for standard TTL, ±25mA for 74HC04, as shown in the variants table above). That current budget is shared across everything the output drives -- an LED, a resistor network, and the input pins of any downstream logic gates all draw from the same output.
If you are driving several downstream logic inputs from one 7404 gate rather than a single LED, keep the combined load well under the output's rated current, and remember that TTL inputs draw a small but nonzero current even when idle. When a design needs to fan out to many gates or drive a load close to the output's limit, it is more reliable to buffer through a dedicated driver IC or a transistor than to push a single logic gate output to its rated maximum. This keeps the output voltage levels clean and avoids the sagging Voh/Vol symptoms described in the troubleshooting table above.
Creating a 7404 Pinout Diagram
CircuitDiagramMaker's IC component tool lets you place a 7404 DIP symbol on a schematic with labeled pins, draw connections to signal sources and loads, and verify the logic flow visually. Useful for documenting any design that uses multiple gates from the same package.
- Place the IC symbol and label all six gates
- Wire unused inputs to VCC or GND (document this explicitly)
- Add the bypass capacitor at VCC/GND pins
- Export as a PNG or PDF for project documentation
Create your own 7404 pinout diagram -- free
Key Takeaways
- The 7404 is a 14-pin DIP hex inverter: six independent NOT gates, VCC on pin 14, GND on pin 7.
- Every gate has one input (A) and one output (Y): HIGH in gives LOW out, LOW in gives HIGH out.
- Always connect pin 14 to VCC and pin 7 to GND -- no connections means no operation.
- Add a 0.1µF bypass capacitor between VCC and GND as close to the chip as possible.
- Tie unused inputs to VCC or GND; never leave them floating, especially with CMOS variants.
- For modern 3.3V or 5V work, prefer the 74HC04 (2--6V supply) or 74HCT04 (5V, TTL-compatible inputs) over the original 7404.
- Each output can drive up to 25mA (74HC04) -- enough for one LED; use a transistor for higher current loads.
Frequently asked questions
What happens if you leave a 7404 input floating?
A floating input sits at an undefined voltage instead of a clean HIGH or LOW, which can make the output oscillate or sit at an unpredictable level. On CMOS variants like the 74HC04 it can also pull excess supply current and generate heat. Always tie unused inputs to VCC or GND rather than leaving them unconnected.
Can I use a 74HC04 in place of a 7404?
Yes, in most designs. The 74HC04 is a modern CMOS replacement with the same pinout, faster switching, and a wider supply range (roughly 2V to 6V) than the original TTL 7404. Check that its output drive current and input thresholds suit your specific circuit, especially if you're mixing it with older TTL logic.
Is the 7404 the same as a NOT gate IC?
Yes. The 7404 contains six independent NOT gates (inverters) in one 14-pin package. Each gate has one input pin and one output pin, and the output is always the logical opposite of the input -- HIGH in produces LOW out, and LOW in produces HIGH out.
What voltage does the 7404 need to operate?
The original standard TTL 7404 needs roughly 4.75V to 5.25V on VCC (pin 14) with GND on pin 7. CMOS variants like the 74HC04 tolerate a much wider range, typically around 2V to 6V, which makes them a better fit for 3.3V microcontroller projects.
Can the 7404 drive an LED directly?
Yes, with a current-limiting series resistor. A standard 7404 output can sink about 16mA, and a 74HC04 can sink or source around 25mA, both of which are enough for a single standard LED. For multiple LEDs or higher-current loads, buffer the output through a transistor instead of overloading the gate.
Why is pin 7 ground and pin 14 power on the 7404 instead of the corner pins?
This layout follows the standard 7400-series DIP pinout convention, where power and ground sit at diagonally opposite corners of the package rather than adjacent pins. It's consistent across most 14-pin logic chips in the family, which is why datasheets and pinout diagrams for related ICs look similar at a glance.