OPTO•USB's port connection is sufficient to power the transmitter unit (TX). USB 1.1 ports will require an external power input. The receiver unit (RX) requires external power for the optical demodulation circuits. Purchase cables of longer length than the short 12" (80cm) cable shipped with OPTO•USB
Specifications: USB A Male to 3.5mm x 1.35mm DC Plug Power Cable. Nickel plated.