Parts
Part pages
One page per component, written by hand from the manufacturer's own datasheets. Many parts ship in more than one package, and the pin order can change between them, so each package gets its own pinout with the datasheet and page number it was read from.
We don't use datasheet aggregators or distributor listings as sources. A test runs on every build and fails if a package has no manufacturer datasheet page behind it, if a datasheet link points anywhere but the maker's own site, or if a suggested substitute has no datasheet of its own.
51 part pages
Small-signal transistors
2N2222 transistor: pinout for every package, ratings and substitutes
The pin order depends on the package: P2N2222A is C-B-E and PN2222A is E-B-C, the exact reverse. The page has the pinout of all four variants, their ratings and gain, a worked 100 mA switch, and substitutes.
Packages: TO-92, TO-18, SOT-23 · Checked against 7 manufacturer datasheets
Background: The bipolar transistor
2N2907A PNP transistor: pinout, ratings and a 12 V high-side switch
The PNP partner of the 2N2222A: E-B-C pins, 60 V and 600 mA on paper. As a TO-92 switch it is comfortable up to about 150 mA.
Packages: TO-92, SOT-23 · Checked against 2 manufacturer datasheets
Background: The bipolar transistor
2N3904 transistor: pinout, ratings, gain and substitutes
E-B-C in TO-92, base-emitter-collector by pin number in SOT-23. Rated 200 mA, but saturation is only specified up to 50 mA, so the worked switch stops there.
Packages: TO-92, SOT-23 · Checked against 6 manufacturer datasheets
Background: The bipolar transistor
2N3906 PNP transistor: pinout, ratings and a high-side switch
The PNP partner of the 2N3904: E-B-C pins, 40 V and 200 mA. A BC557 in its place goes in back to front.
Packages: TO-92 · Checked against 3 manufacturer datasheets
Background: The bipolar transistor
BC337 transistor: pinout, ratings, a 250 mA switch and the BC327
An 800 mA, 45 V NPN in TO-92 with the BC547 pin order, so it drops into a BC547 footprint when the load outgrows 100 mA.
Packages: TO-92 · Checked against 2 manufacturer datasheets
Background: The bipolar transistor
BC547 transistor: pinout, gain groups, ratings and substitutes
Collector, base, emitter from the left, the reverse of the 2N3904. The A, B or C suffix sets the gain band, and two makers rate the same part 500 or 625 mW.
Packages: TO-92 · Checked against 4 manufacturer datasheets
Background: The bipolar transistor
BC547 vs 2N2222 vs 2N3904: the same job, mirrored pins
Three small NPN transistors that do the same job with mirrored pins. The BC547 is C-B-E and stops at 100 mA; the 2N3904 and 2N2222A are E-B-C and take 200 and 600 mA.
Packages: TO-92 · Checked against 5 manufacturer datasheets
Background: The bipolar junction transistor
BC557 PNP transistor: pinout, ratings, a high-side switch and the BC558
The PNP partner of the BC547, with the same C-B-E pins. It switches the positive side of a load, but only from a pin that can reach its own supply.
Packages: TO-92 · Checked against 3 manufacturer datasheets
Background: The bipolar transistor
S8050 transistor: pinout, ratings, a 3.3 V switch and the S8550
A 500 mA NPN in TO-92 with E-B-C pins, the reverse of the BC547. Good for 100 to 200 mA loads from a microcontroller pin.
Packages: TO-92, SOT-23 · Checked against 3 manufacturer datasheets
Background: The bipolar transistor
Power transistors
BD139 and BD140: pinout, ratings, a 5 V pin switch, heat, and the push-pull pair
An 80 V, 1.5 A transistor in a small TO-126 body, sold in pairs with the PNP BD140. The pins run E-C-B, not the B-C-E of a TO-220, and above about a watt it needs a heatsink.
Packages: TO-126 · Checked against 2 manufacturer datasheets
Background: The BJT as a switch
TIP120 Darlington transistor: pinout, ratings, a 5 V pin switch, TIP122 and TIP127
A Darlington in a TO-220: a 5 V pin switches amps with a few milliamps of base current, but up to 2 V stays across it, so it runs hot.
Packages: TO-220 · Checked against 3 manufacturer datasheets
Background: The Darlington pair
TIP31C and TIP32C: pinout, ratings, base drive from a 5 V pin, heat, and the push-pull pair
A 100 V, 3 A NPN power transistor in a TO-220, paired with the PNP TIP32C. Its gain floor is 25 at 1 A and 10 at 3 A, so a microcontroller pin alone can switch only a few hundred milliamps.
Packages: TO-220 · Checked against 1 manufacturer datasheet
Background: The BJT as a switch
MOSFETs
2N7000 MOSFET: pinout, ratings, a 5 V relay switch, BS170 and 2N7002
A 60 V, 200 mA N-channel MOSFET in TO-92, pins S-G-D. Rated at 4.5 V on the gate, so a 5 V pin drives it; a 3.3 V pin is not guaranteed to.
Packages: TO-92, SOT-23 · Checked against 3 manufacturer datasheets
Background: The MOSFET
IRF520 MOSFET: pinout, ratings, and gate drive from Arduino
Gate, drain, source from the left, and the tab is drain. A 100 V part rated only at 10 V on the gate, which is why the Arduino module built on it runs warm or not at all.
Packages: TO-220 · Checked against 4 manufacturer datasheets
Background: The MOSFET
IRF540N MOSFET: pinout, ratings, 5 V gate drive and the IRF9540N
Gate, drain, source from the left, tab is drain. A 100 V, 44 mΩ part rated only at 10 V on the gate, with its P-channel partner, the IRF9540N.
Packages: TO-220 · Checked against 4 manufacturer datasheets
Background: The MOSFET
IRFZ44N vs IRLZ44N: same pins, different gates
Same TO-220 pins, different gates. The IRLZ44N is specified at 5 V and 4 V on the gate, the IRFZ44N only at 10 V, so the swap works one way more often than the other.
Packages: TO-220 · Checked against 2 manufacturer datasheets
Background: The MOSFET
Thyristors, triacs and optocouplers
PC817 optocoupler: pinout, CTR ranks, ratings and a worked interface
Anode, cathode on one side, emitter, collector on the other. The letter after PC817 is its CTR rank, and the minimum CTR, not the typical one, decides how big the pull-up must be.
Packages: DIP-4 · Checked against 1 manufacturer datasheet
Background: Phototransistors and optocouplers
Diodes
1N4007 vs 1N4148 vs 1N5819: three diodes, three different jobs
The three diodes in almost every parts drawer, and they are not interchangeable. The 1N4007 blocks 1000 V and recovers slowly. The 1N4148 switches in 4 ns at small currents, and the 1N5819 drops half a volt less than a 1N4007 up to 40 V.
Packages: DO-41, DO-35 · Checked against 6 manufacturer datasheets
Background: The diode
Regulators and references
7805 regulator: pinout, the 2 V dropout and the heat sink
Input, ground, output from the left, and the tab is ground. It needs about 2.5 V of headroom and turns all the rest into heat, so most of the design work is the heat sink.
Packages: TO-220 · Checked against 2 manufacturer datasheets
Background: Linear regulators
7805 vs LM317 vs AMS1117: three linear regulators, three different jobs
All three burn the extra voltage as heat, and each suits a different job. The 7805 gives a fixed 5 V with its tab on ground, the LM317 sets any voltage from 1.25 V to 37 V with two resistors, and the AMS1117 makes 3.3 V from 5 V with 1.4 V of headroom at most.
Packages: TO-220, SOT-223 · Checked against 3 manufacturer datasheets
Background: Linear regulators
AMS1117 regulator: pinout, dropout, the output capacitor and heat
Ground, output, input from the left, and the tab is the output. It needs up to 1.4 V of headroom and a proper capacitor on the output, and it cannot shed much heat.
Packages: SOT-223 · Checked against 3 manufacturer datasheets
Background: Linear regulators
LM2596 buck regulator: pinout, ratings, a 12 V to 5 V design and the blue module
A 150 kHz, 3 A step-down regulator in a 5-pin TO-220. TI and onsemi disagree on the switch drop and current limit, and at 2 A the bare TO-220 already wants a heat sink.
Packages: TO-220-5 · Checked against 2 manufacturer datasheets
Background: Switching regulators
LM2596 vs 7805: when a switching regulator beats a linear one, and when it doesn't
Both give a steady 5 V from a higher voltage, in opposite ways. The 7805 burns the extra voltage as heat and stays quiet; the LM2596 switches at 150 kHz, reaches 80 % efficiency at 12 V in and 3 A out, and needs an inductor, a Schottky diode and careful layout.
Packages: TO-220-5, TO-220 · Checked against 2 manufacturer datasheets
Background: Switching regulators
LM317 regulator: pinout, the R1/R2 formula, heat and the LM337
Adjust, output, input from the left, and the tab is the output. Two resistors set the voltage; the heat it has to lose decides the rest. The LM337 swaps the middle pin.
Packages: TO-220 · Checked against 4 manufacturer datasheets
Background: Linear regulators
TL431 shunt reference: pinout, the output formula and the series resistor
A 2.495 V reference that two resistors can set anywhere up to 36 V. It needs at least 1 mA through it, and its TO-92 pins read REF, anode, cathode.
Packages: TO-92, SOT-23 · Checked against 2 manufacturer datasheets
Background: Voltage references
Op-amps, timers and comparators
741 op-amp (uA741, LM741): pinout, ratings, slew rate and offset
The general-purpose op-amp that most textbooks and lab manuals still use. It needs a split supply of at least ±5 V, and its 0.5 V/µs slew rate limits a full-swing output to a few kilohertz.
Packages: DIP-8, SOP-8 · Checked against 2 manufacturer datasheets
Background: The op-amp
LM358 dual op-amp: pinout, single-supply limits, the LM358A and the LM324
Two op-amps built for one supply. The inputs work down to the negative rail, the output gets within millivolts of it, and the top 1.5 V of the supply is out of reach for both.
Packages: DIP-8, DIP-14 · Checked against 2 manufacturer datasheets
Background: The op-amp
LM358 vs 741 vs TL072: three general-purpose op-amps and where each one fails
Three op-amps that look alike in a parts drawer. The LM358 senses signals at ground on one supply, the TL072 is fast with almost no input current, and the 741 has a different pinout.
Packages: DIP-8 · Checked against 4 manufacturer datasheets
Background: The op-amp
LM358 vs LM393: which one for your threshold circuit, and what breaks when you swap them
An op amp and a comparator with the same pin order. The LM393 switches fast and needs a pull-up; the LM358 drives its output both ways and can amplify.
Packages: DIP-8 · Checked against 2 manufacturer datasheets
Background: The comparator
LM393 dual comparator: pinout, the pull-up, hysteresis, the LM339 and the LM2903
Two comparators whose outputs can only pull down. A pull-up resistor sets the high level, so a 5 V chip can talk to a 3.3 V board, and a feedback resistor stops it chattering.
Packages: DIP-8, DIP-14 · Checked against 2 manufacturer datasheets
Background: The comparator
NE555 timer: pinout, ratings, CMOS versions, the NE556 and a worked flasher
Pin 1 is ground and pin 8 the supply, the same on every 555. The CMOS versions share the pins but not the output drive, and the NE556 is two timers in one 14-pin package.
Packages: DIP-8, DIP-14 · Checked against 6 manufacturer datasheets
Background: The 555 timer
NE555 vs TLC555: when the CMOS 555 is a drop-in, and when it isn't
The two chips share their eight pins and timing formulas. The TLC555 runs from 2 V on a fraction of the current and goes far faster, but its output sources only about 10 mA, where the NE555 drives 200 mA.
Packages: DIP-8, SOP-14 · Checked against 2 manufacturer datasheets
Background: The 555 timer
TL072 dual JFET op-amp: pinout, input range, ratings and the TL071 and TL074
A dual JFET op-amp with picoamp input current, built for split supplies. Its inputs must stay about 4 V above the negative rail, which is why it misbehaves on a single 5 V supply.
Packages: DIP-8, SOP-8, DIP-14 · Checked against 3 manufacturer datasheets
Background: The op-amp
Logic ICs
74HC logic gates: 74HC00, 74HC02, 74HC04, 74HC08, 74HC14, 74HC32 and 74HC86 pinouts and limits
Seven 14-pin CMOS gate chips that share VCC on pin 14 and ground on pin 7. The 74HC02 NOR puts its output first, and only the 74HC14 has Schmitt-trigger inputs.
Packages: DIP-14, SOP-14 · Checked against 14 manufacturer datasheets
Background: Logic families
74HC138 3-to-8 decoder: pinout, truth table, an LED select circuit and 16-line expansion
A 16-pin CMOS decoder: three address inputs pull one of eight outputs low while the rest stay high. Three enable pins let two chips make a 4-to-16 decoder with no extra parts.
Packages: DIP-16, SOP-16 · Checked against 2 manufacturer datasheets
Background: Logic levels
74HC165 shift register: pinout, read order, eight buttons on three pins and chaining
A 16-pin CMOS shift register that works the other way round from the 74HC595: it grabs eight inputs at once, then clocks them out one at a time on a single pin. Chips chain through SER for 16, 24 or more inputs on the same three wires.
Packages: DIP-16 · Checked against 1 manufacturer datasheet
Background: Logic levels
74HC245 bus transceiver: pinout, DIR and OE, bus fights and the 3.3 V question
A 20-pin CMOS chip with eight two-way buffers between an A side and a B side. DIR picks the direction for all eight at once and OE disconnects them. Often used as an LED or bus buffer, and often misused as a 3.3 V to 5 V level shifter.
Packages: DIP-20 · Checked against 3 manufacturer datasheets
Background: Logic levels
74HC595 shift register: pinout, timing, eight LEDs from three pins and daisy-chaining
A 16-pin CMOS shift register with an output latch: clock in eight bits on one pin, latch them onto eight outputs at once. Chips chain through pin 9 for 16, 24 or more outputs on the same three wires.
Packages: DIP-16, SOP-16 · Checked against 2 manufacturer datasheets
Background: Logic levels
74HC74 dual D flip-flop: pinout, PRE and CLR, divide-by-2 speed and a push-button toggle
A 14-pin CMOS chip with two D flip-flops, each with its own clock, data, preset and clear. Used to halve a clock, make a push button toggle, or hold a bit until the next edge.
Packages: DIP-14 · Checked against 3 manufacturer datasheets
Background: Logic levels
Drivers, interface and microcontrollers
24C02 EEPROM (24LC02B, AT24C02): pinout, I2C address and pull-ups
A 256-byte I2C EEPROM in an 8-pin package, used to keep settings and calibration through power cuts. Writes take up to 5 ms, and the A0 to A2 pins set the address on some makers’ parts but do nothing on others.
Packages: DIP-8, SOP-8 · Checked against 2 manufacturer datasheets
Background: Pull-up and pull-down resistors
AT89S52 8051 microcontroller: pinout, ports, ISP pins and a minimal circuit
All 40 pins, with Port 0 open drain and the three ISP pins on Port 1. Why 11.0592 MHz gives exact baud rates, and a 10 kΩ / 10 µF reset that holds RST high for about 36 ms.
Packages: DIP-40 · Checked against 3 manufacturer datasheets
Background: Crystals and resonators
ATmega328P: DIP-28 pinout, Arduino pin map, ratings and a standalone circuit
All 28 pins of the DIP chip with their port names and Arduino numbers. 16 MHz needs at least 3.78 V, and one pin is specified to 20 mA, not the 40 mA in the maximum ratings.
Packages: DIP-28 · Checked against 2 manufacturer datasheets
Background: Crystals and resonators
ATtiny85: DIP-8 pinout, clock limits, pin current and programming
Six I/O pins on an 8-pin chip, one of them RESET. Each pin is specified to 10 mA at 5 V, and a new chip runs at 1 MHz until you change its fuses.
Packages: DIP-8 · Checked against 1 manufacturer datasheet
Background: Pull-up and pull-down resistors
CH340G USB to serial chip: pinout, the 12 MHz crystal, 5 V or 3.3 V wiring, and the CH340C
The USB to serial chip on most low-cost Arduino and ESP boards. It needs a 12 MHz crystal and one capacitor on 5 V, and runs from 3.3 V with V3 tied to VCC. The CH340C drops the crystal.
Packages: SOP-16 · Checked against 1 manufacturer datasheet
Background: Logic levels
ESP32 and ESP32-WROOM-32E: pinout, strapping pins, ratings and a minimal circuit
Every pad of the ESP32-WROOM-32E and the QFN chip inside it, with the five strapping pins and what each sets at reset. The module draws 379 mA peaks when it transmits and no pin takes 5 V.
Packages: QFN-48, Module-38 · Checked against 4 manufacturer datasheets
Background: Logic levels
L293D motor driver: pinout, wiring, the voltage it loses and how hot it gets
A 16-pin chip with four half-H drivers and built-in clamp diodes: two of them make an H-bridge, so one chip runs two DC motors forward and back, or one stepper. 600 mA per channel, motor supply up to 36 V.
Packages: DIP-16 · Checked against 1 manufacturer datasheet
Background: Motor driver ICs
LM35 temperature sensor: pinout, grades, accuracy and the ADC trap
Supply, output, ground from the left with the flat face toward you, and 10 mV per degree. On an Arduino read it against the 1.1 V reference, not 5 V, or each step is half a degree.
Packages: TO-92, SOP-8, TO-220 · Checked against 3 manufacturer datasheets
Background: ADCs and DACs
MAX232: pinout, the four capacitors, RS-232 levels and what changes on a 3.3 V board
Two line drivers and two receivers that turn 5 V UART logic into ±7 V RS-232 and back, powered from 5 V alone by a charge pump and four capacitors.
Packages: DIP-16 · Checked against 3 manufacturer datasheets
Background: Reading IC datasheets
PIC16F877A: DIP-40 pinout, MCLR reset, 20 MHz crystal and ICSP pins
33 I/O pins on a 40-pin DIP, two supply pairs, and RB3 set aside for low-voltage programming until you clear the LVP bit. Runs to 20 MHz on 4.0 to 5.5 V.
Packages: DIP-40 · Checked against 1 manufacturer datasheet
Background: Crystals and resonators
ULN2003 vs L293D: which driver for your relay, stepper or DC motor
Seven low-side switches against four half-H drivers in the same 16-pin package. The ULN2003A switches relays and unipolar steppers; the L293D reverses motors.
Packages: DIP-16 · Checked against 2 manufacturer datasheets
Background: Motor driver ICs
WS2812B addressable LED: pinout, timing, current and 3.3 V data
VDD, DOUT, VSS and DIN round the 5050 package, with the cut corner at ground. At 5 V its data input wants 3.15 V, more than an ESP32 guarantees.
Packages: 5050 · Checked against 1 manufacturer datasheet
Background: LED circuits
Datasheets get revised. Each part page lists the revision it was checked against; if your copy is newer and a number disagrees, the datasheet wins. Tell us and we will fix the page. For values worked out from a formula, try the calculators.
To read a resistor's bands, use the resistor color code calculator. It handles 4, 5 and 6-band parts and gives the nearest standard value.
Wiring up an 8051? The 8051 pin diagram and pin description lists all 40 pins in one table, with what each one connects to.