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.
Transmitting information on public broadcast bands typically prohibited and requires a broadcast license. Some countries (i.e. US) allow transmissions as long as the transmitted distance is low.
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.
Always make sure whether operating this board is legal in your country before you power it on. There may be substantial fines.
Pins
The board comes with four solder pads labeled on the front.
| Pin | Description |
|---|---|
| GND | negative voltage |
| VCC | 3.0-5.0V |
| SDA | I2C Interface |
| SCL | I2C Interface |
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.
| Item | Description |
|---|---|
| Voltage | 1.8-6V |
| Operational Current | <17mA |
| Standby Current | <3uA |
| Frequency | 70-108MHz |
| RF Power | max 1.3mW |
| Interface | I2C, 5V tolerant |
| I2C Address | 0x0111110 |
| Modulation | Wide-FM |
| Chip | KT0803L from KTMicro |
| Features | 20bit Audio ADC, DSP Core, 24dB PGA |
| Size | 27.7x26.4x7mm |
KT0803L
The chip that drives this board is the KT0803L from KTMicro.
The picture below shows the main chip, and close to the VCC connector, you see the 662K 3.3V voltage regulator that takes the 1.6-6.0V input voltage and converts it to the 3.3V required by the chip:
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
Software Libraries
Here are a few software libraries on github that produce the I2C control messages required to set up the transceiver chip:
Data Sheet
KT0803K Radio-Station-on-a-Chip
KT0803L Radio-Station-on-a-Chip
662K 3.3V Voltage Regulator
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(content created Apr 19, 2024)