Usage Tips:Specification: Charging: 5V 1A (4.75V-5.5V 1A10%) AUX connection: 3.5mm audio connector, switch: ON-OFF switch FM display: 88.1Hz-107.9Hz, FM connection: connect when the frequency is the same Audio input: 3.5mm audio connector, volume adjustment: none Audio output: FM band connection output, frequency adjustment: press to increase the frequency. reduces frequency Feature: Encapsulated with a full plastic shell, strong buckle connection. The built-in 300mA powerful polymer battery cell provides a strong and continuous power supply. 3.5mm provides FM signal source. Please select a frequency band without a radio station for connection. The key digital tube displays the current frequency band and volume. Fine workmanship and good performance. Easy to use. Durable in use. Package included: 1pc x FM Transmitter