SMD marking codes

Device codes — type the two or three characters printed on a SOT-23 transistor or diode (1AM, 1F, 702, A7, J3Y…) or part of a part number; pick the package to narrow it. Each match shows the part, what it is, its pins and a drawing of the package with the marking upright: SOT-23 pin 1 bottom-left, pin 2 bottom-right, pin 3 at the top; two-terminal parts have the band at the cathode. The list is deliberately small and honest: about 45 parts you meet on modules and dev boards, each from its maker’s datasheet (onsemi, Nexperia, Diodes Inc.) or the SMD Codebook, with the maker named. Codes are re-used — the same two letters can be a transistor from one maker and a zener from another — so check the package and the circuit, and confirm with a datasheet or a meter’s diode test.

Resistors — 3-digit (472 = 4.7 kΩ, usually 5 %), 4-digit (4702 = 47 kΩ, 1 %), R for the decimal point (4R7), and EIA-96 for small 1 % chips: two digits pick the value from the E96 series, the letter multiplies it (01C = 10 kΩ). The whole EIA-96 table is shown with your code highlighted. Decoding is the same as the resistor colour code tool’s.

Capacitors — the 3-digit pF code with a tolerance letter (104K = 100 nF ±10 %), the EIA-198 two-character code (S4 = 47 nF; letters are case-sensitive), and moulded tantalum markings: a pF code and a voltage letter (107A = 100 µF 10 V; the bar is the + end).

The device list covers common small-signal parts only — no regulators, op-amps or ICs (their markings are maker-specific and often a date code). Absence here means nothing.

Plain SMD ceramics usually carry no marking at all; measure them.

Some makers swap pin 1 and 2 roles or use reversed packages (SOT-23R); the datasheet decides.