Si4707 Breakout Hardware Support
This wiki page covers the SparkFun Si4707 Breakout Board hardware. Everything from explanations of the schematic and pin-out, to usage hints is discussed here.
Click the image below to see a bigger image, or click here to see a pdf of the schematic.
There are two main components to the Si4707 breakout: the Si4707 weather band radio receiver IC and a TPA6111A2 stereo headphone audio amplifier. The audio output is sent to a 3.5mm audio jack, but can alternatively be taken from the 3-pin header on the side of the board.
The Si4707 is clocked with a 32.768kHz crystal. The left and right analog audio signals are connected to the audio amplifier. The IC's RF input (FMI) is filtered and connected, through a jumper, to a headphone antenna. A jumper on the bottom of the board allows you to instead connect this input to an externally connected antenna. The supply voltage (VDD) and interface supply voltage (Vio) are connected together on the PCB. The remaining control pins are broken out to a 0.1" spaced header.
The gain of the TPA6111 is set to -2.35.
On the main header, the following pins are broken out:
- 3.3V - The supply voltage input. This will go to both the VDD and Vio pins of the Si4707. As such, the supply voltage should be between 1.5 and 3.6V.
- GND - This supplies both the digital ground and rf ground of the Si4707.
- SDIO - Serial data input/output. This pin is pulled up to 3.3V through a 4.7k resistor on the PCB.
- SCLK - Serial clock input. This pin is pulled up to 3.3V through a 4.7k resistor on the PCB.
- SEN - Serial enable input. If used in I2C mode, this pin selects the 7-bit address of the IC. In SPI mode, this is the chip-select input. This pin is pulled up to 3.3V through a 4.7k resistor on the PCB.
- RST - Device reset input (active low). This pin is pulled up to 3.3V through a 4.7k resistor on the PCB.
- GPO1 - General purpose output 1.
- GPO2 - General purpose output 2. This pin also serves as an interrupt output if so configured.
Other pins not on the main 8-pin header are:
- ANT - This is connected to the FMI input of the Si4707 - the WB RF input. If you'd like to use an external antenna, select this output pin on the jumper (on the bottom of the board, near the pin).
- L and R - These are the analog audio outputs from the headphone amplifier. If you'd rather not use the 3.5mm audio jack, you can use these headers instead.
Power to the Si4707 breakout should be supplied to the 3.3V and GND pins.
The input supply on the Si4707 Breakout Board is unregulated, so - because VDD is connected to the interface supply voltage (Vio) - the input voltage limits should be constrained by the Vio voltage constraints (1.5V to 3.6V).
The breakout board defaults to using the long headphone cable as an antenna. While not usually the optimal length for WB wavelengths, headphone cables should work to receive nearby stations. This configuration works for evaluation purposes, but for better signal strength you may want to connect your own whip antenna to the board.
A simple 1/4-wave whip antenna can be constructed with a specifically sized wire - about 46cm should do. You'll also need to cut the jumper between the middle pad and the "HP" pad, and short the middle pad to the "EXT" side:
Caveat: Because of the way the jumper is configured, selecting the external antenna on the jumper disconnects the 3.5mm audio jack from a common ground. This will usually result in very low, unstable volume emanating from the audio jack. If you want to use both an external antenna, and the 3.5mm audio jack a small jumper wire should be connected from the GND pin to the common pin on the jack.
