I2C FM-Transmitter Board For Sending Audio Input To Car Radios
HW-158 is a Wide-FM transmitter that can send audio input to a radio frequency in the range of public broadcasting 70-116MHz.
It is controlled by a I2C interface, uses the latest KT0803L “Radio-Station-on-a-Chip” and requires an external microcontroller to operate.
Boards like HW-158 take this into account and emit with very low RF power sufficient for distances of just a few meters.
With these boards, external audio sources can i.e. be fed into car radios that have no auxiliary input:
An external audio source is connected via 3.5mm cinch plug into the HW-158 module. The module then sends the audio to a preset VHF radio frequency that can be received by any FM radio set in close vicinity as if it were a public broadcasting radio station.
Technical Data
The actual transmitter chip used by the board requires a voltage of 1.6-3.6V.
The breakout board adds a 662K (XC6206P332MR) 3.3V voltage regulator that takes 1.8-6V and converts it to 3.3V.

KT0803L
The chip that drives this board is the KT0803L from KTMicro.
KT0803L is a hardware-compatible enhanced version of KT0803K and KT0803M which in turn base on the KT0801.
These are the added features found in KT0803L over its predecessors
• Software Standby
• Automatic Amplifier Power-Down On Silence
• ALC (Automatic Level Control)
• Better SNR (Stereo 66dB)
• Improved Audio Frequency Response
• Software-controlled XTAL selection