🔌 IC Pinouts
Pin functions and diagrams for the most common ICs — 555 timer, LM317, LM741 op-amp, 7400-series logic, and Arduino Uno.
NE555 / LM555 Timer
DIP-8 · Supply: 5–15 V (NE555) or 1.5–15 V (CMOS 7555)
Astable: f = 1.44/((Ra+2Rb)×C)
- 1GND — Ground reference
- 2TRIGGER — Starts timing when pulled below ⅓ Vcc (active LOW)
- 3OUTPUT — HIGH during timing; can source/sink 200 mA
- 4RESET — Forces OUT LOW when pulled LOW; tie to Vcc if unused
- 5CONTROL VOLTAGE — Sets ⅔ Vcc threshold; bypass with 10 nF to GND if unused
- 6THRESHOLD — Stops timing when voltage > ⅔ Vcc
- 7DISCHARGE — Open-collector; discharges timing capacitor
- 8Vcc — Positive supply (4.5–15 V)
LM317T Adjustable Voltage Regulator
TO-220 package · Output: 1.25–37 V · Max current: 1.5 A
Vout = 1.25 × (1 + R2/R1) (R1 = 240 Ω)
Connect R1 (240 Ω) between OUT and ADJ. Connect R2 (variable) between ADJ and GND. Vout is set by the ratio R2/R1.
- 1ADJ — Connect voltage divider here to set output voltage
- 2OUTPUT — Regulated output voltage
- 3INPUT — Unregulated input (must be ≥3 V above Vout)
Common values: Vout=5V: R1=240Ω, R2=720Ω. Vout=12V: R1=240Ω, R2=2.1kΩ. Add 0.1μF on input, 1μF on output.
LM741 Operational Amplifier
DIP-8 · Supply: ±5 V to ±18 V · Open-loop gain: 200,000 typical
Inv: Av = −Rf/Ri Non-inv: Av = 1+Rf/Ri
- 1Offset Null 1 — Connect 10kΩ pot between pins 1 & 5, wiper to V−
- 2Inverting Input (IN−) — Feedback goes here for negative feedback configurations
- 3Non-Inverting Input (IN+) — Signal input for non-inverting configurations
- 4V− — Negative supply (e.g. −12 V)
- 5Offset Null 2 — See pin 1
- 6OUTPUT — Amplified output signal
- 7V+ — Positive supply (e.g. +12 V)
- 8N/C — No connection
74xx Series Logic Family
Vcc always pin 14 (DIP-14) or 20 (DIP-20). GND always pin 7 (DIP-14) or 10 (DIP-20). All 74HCxx variants are pin-compatible with 74LSxx.
| Part | Function | Gates/Pkg | Logic |
|---|---|---|---|
| 7400 | Quad 2-input NAND | 4× | Y = ̅(A·B) |
| 7402 | Quad 2-input NOR | 4× | Y = ̅(A+B) |
| 7404 | Hex Inverter (NOT) | 6× | Y = Ā |
| 7408 | Quad 2-input AND | 4× | Y = A·B |
| 7432 | Quad 2-input OR | 4× | Y = A+B |
| 7486 | Quad 2-input XOR | 4× | Y = A⊕B |
| 7474 | Dual D Flip-Flop | 2× | Q→D on ↑CLK |
| 74138 | 3-to-8 Line Decoder | 1× | Active-low outputs |
| 74595 | 8-bit Shift Register | 1× | Serial in, parallel out |
Variants: 74LS (Low-power Schottky, 5V), 74HC (High-speed CMOS, 2–6V), 74HCT (CMOS, TTL-compatible inputs), 74AC (Advanced CMOS). Pin-for-pin compatible within same number.
Arduino Uno R3 Pin Reference
ATmega328P · 5 V logic · 14 digital I/O · 6 analog inputs · 32 KB flash
| Pin(s) | Type | Description |
|---|---|---|
| D0 (RX) / D1 (TX) | Digital / Serial | UART serial. Avoid using when uploading sketches. |
| D2 / D3 | Digital / Interrupt | External interrupt capable (INT0, INT1). D3 also PWM. |
| D3,D5,D6,D9,D10,D11 | PWM (marked ~) | 8-bit PWM @ 490–980 Hz via analogWrite() |
| D10–D13 | SPI | SS, MOSI, MISO, SCK. D13 also drives built-in LED. |
| A4 (SDA), A5 (SCL) | I²C / Analog | I²C bus. Also usable as analog inputs A4/A5. |
| A0–A5 | Analog Input | 10-bit ADC. 0–5V → 0–1023 via analogRead(). |
| 5V, 3.3V, GND | Power | 5V (500 mA max from USB), 3.3V (50 mA max). |
| Vin | Power Input | 6–12 V unregulated input. Onboard 5 V regulator feeds from here. |
| RESET | Control | Pull LOW to reset the microcontroller. |
| AREF | Analog Ref | External voltage reference for ADC precision. |
Max current: Each I/O pin: 40 mA. All pins combined: 200 mA. Always use a 220–1000 Ω resistor when driving LEDs directly from Arduino pins.