Remove the Arduino and make the circuit really simple.

Right, so plug in the Arduino into where 3.3V is, and set the pin to HIGH, and LED is on. Using Ohm's law again, and factoring in the 0.7v drop from V b to V e we have 12k Ohms. My understanding is that I c is I b x h fe. Using Ohm's law, that gives us a resistor of 150 ohms, correct so far?įor the sake of easy math, we'll say h fe is 100. Using a standard, run of the mill, red LED, we say the voltage drop is 2V, and requires 20mA.

Simulate this circuit – Schematic created using CircuitLab To test out the circuit, I figured I'd substitute an LED for the time being. Obviously the Arduino I'm using doesn't have the voltage to drive the 5V relay, so that's where the 2N2222 comes in. The A probably means it's a 2N2222A.I'm looking to drive a relay on a 5V rail from an Arduino 3.3V pin. Note that in your specific case, the code you're looking for is probably just '331'. If the manufacturer no longer exists, or has gotten bought up by another company decades ago, you're probably just out of luck. If they don't, you'd have to contact the manufacturer and ask. Even if you do know the manufacturer, these codes are meant mostly for the manufacturer's internal reference, so they might not be explained on the datasheet. There is no standard, so without knowing the manufacturer, you're out of luck. But fitting that along with the part number on a TO-92 or TO-18, let alone a SOT-23 or SC-70, is pretty tough, so other codes are used instead.

On parts with more room than a TO-92 or TO-18 provides, you might get a one-digit factory code for which factory the part was made in, combined with a four-digit date code consisting of the last two digits of the year and two digits indicating which week of the year it was made in. The usual practice is to put some manufacturer-specific code that identifies which lot the device came from.

2n2222 transistor download