Multi-Band Receiver On A Chip Controlled By Arduino

The Silicon Labs Si4735 is a single-chip solution for receiving AM, FM, and shortwave radio. With a bit of hacking, it even supports single sideband (SSB). All you’ve got to do is provide it with a suitable control interface, which [Ricardo Lima Caratti] has done with his recent project.

Using an Arduino Pro Mini, a handful of buttons, and a standard TFT display, [Ricardo] has put together a serviceable little receiver with a fairly impressive user interface. We especially like the horizontal bars indicating the signal to noise ratio and received signal strength. The next evolution would be to put this whole rig into some kind of enclosure, but for now he seems content to control the action with a handful of unlabeled buttons on a piece of perfboard.

Of course, the presentation of this receiver isn’t really the point; it’s more of a proof of concept. You see, [Ricardo] is the person who’s actually developed the library that allows you to control the Si4735 from your microcontroller of choice over I2C. He’s currently tested it with several members of the official (and not so official) Arduino family, as well as the ESP32.

The documentation [Ricardo] has put together for his MIT licensed Arduino Si4735 library is nothing short of phenomenal. Seriously, if all open source projects were documented even half as well as this one is, we’d all be a few notches closer to world peace. Even if you aren’t terribly interested in adding shortwave radio reception to your next project, you’ve got to browse his documentation just to see where the high water mark is.

We actually first heard about this library a few days ago when we covered another receiver using the Si4735 and [Ricardo] popped into the comments to share some of the work he’d been doing to push the state-of-the-art forward for this promising chip.

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All Band Radio Uses Arduino And Si4730

It is getting harder and harder to tell homemade projects from commercial ones. A good case in point is [Mirko’s] all band radio which you can see in the video below the break. On the outside, it has a good looking case. On the inside, it uses a Si4730 radio which has excellent performance that would be hard to get with discrete components.

The chip contains two RF strips with AGC, built-in converters to go from analog to digital and back and also has a DSP onboard. The chip will do FM 64 to 108 MHz and can demodulate AM signals ranging from 153 kHz to 279 kHz, 520 kHz to 1.71 MHz, and 2.3 MHz to 26.1 MHz. It can even read RDS and RBDS for station information. The output can be digital (in several formats) or analog.

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An FM Transceiver From An Unexpected Chip

The Si47xx series of integrated circuits from Silicon Labs is a fascinating series of consumer broadcast radio products, chips that apply SDR technologies to deliver a range of functions that were once significantly more complex, with minimal external components and RF design trickery.  [Kodera2t] was attracted to one of them, the Si4720, which boasts the unusual function of containing both a receiver and a transmitter for the FM broadcast band and is aimed at mobile phones and similar devices that send audio to an FM car radio. The result is a PCB with a complete transceiver controlled by an ATmega328 and sporting an OLED display, and an interesting introduction to these devices.

The Si4720 internal block diagram, from its data sheet.
The Si4720 internal block diagram, from its data sheet.

A look at the block diagram from the Si4720 reveals why it and its siblings are such intriguing devices. On-chip is an SDR complete in all respects including an antenna, which might set the radio enthusiasts among the Hackaday readership salivating were it not that the onboard DSP is not reprogrammable for any other purpose than the mode for which the chip is designed. The local oscillator also holds a disappointment, being limited only to the worldwide FM broadcast bands and not some of the more useful or interesting frequencies. There are however a host of other similar Silicon Labs receiver chips covering every conceivable broadcast band, so the experimenter at least has a good choice of receivers to work with.

If you need a small FM transmitter and have a cavalier attitude to spectral purity then it’s easy enough to use a Raspberry Pi or just build an FM bug. But this project opens up another option and gives a chance to experiment with a fascinating chip.