Through-hole isolation for breadboard and panel
The 6N138M is a single-channel optoisolator in an 8-DIP through-hole package — the 0.300-inch row spacing fits standard perfboard and breadboards, so you can prototype the isolation barrier without a custom PCB. Rated for 5000Vrms isolation between input and output, it separates a low-voltage microcontroller domain from a high-voltage power stage in a motor drive or a 24V PLC input module.
Speed and drive — what the timing numbers mean
Turn-on time is 1µs typical, turn-off is 7.3µs typical — the Darlington output is slower than a phototransistor optoisolator, so this part is best for DC-level isolation, status feedback, and low-speed serial signals up to about 100 kHz, not for high-speed data buses. The base pin is brought out on pin 6, letting you add a speed-up capacitor between base and emitter to reduce turn-off time, or a pull-down resistor to set the switching threshold — useful when the downstream logic has a specific input voltage window.