Combine the Si4844-A10 analog-tuned radio receiver with an Arduino to make a full-featured multiband radio.

The idea of a single chip radio is intriguing. The prospect is especially interesting to me because, frankly, I envy the analog skills I associate with building a radio receiver. When I browsed the circuit literature in the area, I came across the Silicon Labs collection. One of their chips, the Si4844-A10 caught my attention. This receiver has AM/FM/SW capability with all the bells and whistles and it is designed to work with a microprocessor. Best of all, the support components required are mainly associated with the microprocessor display and control functions with only a small amount of antenna support needed. I couldn’t resist taking the plunge.

 

Reference Documents

Familiarity with the chip’s data and application information is strongly encouraged. The three documents linked below are highly recommended for understanding and building the project:

Si4844-A10 datasheet

Programming Guide

Design Guide

 

The Basic Circuit

Radio receiver schematic

Figure 1. The radio receiver schematic

 

Figure 1 presents the basic circuit for the receiver and the schematic is adapted from the Silicon Labs Si4844 datasheet and application notes. I used a reclaimed ferrite loop from a discarded portable AM/FM radio as the required AM antenna. I think that a higher quality and larger ferrite would be an improvement. Q1 is the amplifier for the SW/AM and I also used a reclaimed telescopic antenna in that section. It is notable that the design guide, linked above, gives several alternatives and different approaches for the antenna components.

The variable resistor (VR1) is a critical component since this will be used to adjust the receiver frequency – the tuning knob. It is recommended that a good quality linear potentiometer be used. For the audio out, I chose to use a set of “economical” amplified speakers that I had from a retired desktop PC. Certainly, a simple stereo amplifier could also be used. Everything on the board is 3.3v and all GNDs are connected.

The most difficult part of the construction is probably working with the chip’s SSOP-24 form factor. If you don’t have the experience and equipment to use SMT ICs, the use of a carrier board may be the easiest way to accomplish the task. I had an SSOP-28 carrier board and with a fine point soldering tip and a lot of patience (and some solder braid to undo bridges); I was able to mount the chip so that it could be accessed as a DIL package. The other potentially difficult components to work with are the couple of surface mount ferrite beads and capacitors. These components can also be hand soldered onto a carrier board and treated like a DIL package.

 

SMT components on carrier board

SMT components soldered onto carrier boards

 

Parts list for the main circuit:

Part Description
B1 ferrite bead 2.5 kOhm (100 mHz)
C1,C2,C5 4.7 uf non polarized capacitor
C3,C4 22 pf non polarized capacitor
C6,C7,C9 .1 uf non polarized capacitor
C8 47 uf non polarized capacitor
C10,C11 .47 uf non polarized capacitor
C12,C14 33 nf non polarized capacitor
C13 33 pf non polarized capacitor
C15 10 pf non polarized capacitor
IC1 Si4844-A10 radio receiver
Q1 SS9018 NPN transistor
R1, R2 2.2K
R3 1K
R4,R7 100K
R5 10
R6 120K
R8 100
L1 270 nH Inductor
VR1 100K linear potentiometer
Y1 32.768 kHz crystal
ANT1 ferrite antenna
ANT2 telescopic/whip antenna

 

Connecting an Arduino

The other piece that needs to be considered before powering up the circuit for testing is the Arduino interface. For this component, I chose to use the Arduino Pro Mini, 3v/8Mhz board. This tiny Arduino is entirely 3.3v and is compatible with the Si4448-A10 and that is a chief advantage. The small size of the board is an additional convenience. Connection to the Si4844-A10 is through four lines as described below:

Arduino (3.3v) Si4844-A10

Arduino to Si4844-A10 connections:

A5/SCL SCLK
A4/SDA SDIO
D2 INT
D12 RST

 

Additionally, a standard USB/Serial interface is used to connect the Arduino to a PC for programming. The exact connections will depend a bit upon the serial board that you use, but will include the usual TX, RX and GND connections. In this manner, you can essentially program and test the Si4844-A10 “in circuit”, which facilitates development and experimentation. When completed, however, the connection can be eliminated for a stand-alone multiband radio. Powering both the radio board and the Arduino must be with an external 3.3v regulated power supply. Do not try to power them using the USB/serial board, even if it has a 3.3v output pin— these cannot be depended upon to have the capability to provide the necessary current to drive both the Arduino and the Si4844-A10.

 

Testing the Basic Circuit

Once you have the circuit bread-boarded, the Arduino connected, and the amplified speakers attached, you can run a test program that is included in this article (Si4844_Quick_Test.ino). The program performs a simple test of the circuit that will power up the device, set the band to FM, and provide the chip’s version information. If all goes well, you should be able to tune the radio by turning VR1 and you will see the frequency dynamically displayed on the screen – and, of course, hear the radio output.

 

Screen capture

Screen capture of the test program

 

Once the basic circuit and Arduino connections are functional, construction of the full-featured radio can proceed.

 

Arduino Programming

The Si radio chip in this project is an I2C slave device having a fixed address of 0x11, with the Arduino as the master device. The I2C communication speed of the chip, however, is relatively slow with 50 kHz as the maximum supported speed. Moreover, during a portion of the power up procedure, the speed must not exceed 10 kHz. To meet these requirements, we have to explicitly set the Arduino I2C speed, which is normally too fast for the Si4844-A10. Fortunately, aided by the wealth of documentation on Arduino I2C functions, we can easily accomplish the necessary changes.

Basically, I2C speed, for our purposes, is determined by two dedicated variables in the Arduino software. Those dedicated variables are TWBR and TWSR. Bit 0 and 1 of TWSR control a prescaler that works with the value of TWBR to set the I2C speed. The speed (clock frequency) of the I2C transmissions is calculated by: Frequency = CPU Clock frequency / (16 + (2 * (TWBR) * (Prescaler)). The Arduino Pro mini 3.3v runs at 8 mHz. To set I2C speed to 10 kHz, we use a TWBR value of 98 and we set the prescaler to 4 (by setting only bit 0 of TWSR). Thus, 8,000,000 / (16+(2*98 [TWBR value]*4 [prescaler]))=10,000 or 10 kHz. To set the I2C speed to 50 kHz, we use a TWBR value of 18 and we set the prescaler to 4 (by setting only bit 0 of TWSR). Thus, 8,000,000 / (16+(2*18 [TWBR value]*4 [prescaler]))=50,000 or 50 kHz.

See Nick Gammon’s excellent repository of Arduino I2C information and the Arduino Library documentation for more information on this process. The bottom line, however, is that we can accomplish these I2C speed changes in just a couple of lines of code and you can see those in the test program.

Another important programming consideration is that we need to use an external interrupt service routine in our code. You can read some background on the use of external interrupts here. We use INT0 on the Arduino and, basically, when that pin is set high by the Si4844-A10, the program will execute a simple routine that has been “attached” to the interrupt. All the routine will do is set a flag variable that can be examined and changed in other parts of the code. The Si4844-A10 will issue interrupts (i.e., bring the INT pin high) under certain conditions, most notably when the tuning potentiometer has been changed. Therefore, the Si4844-A10 tells the Arduino that you have moved the tuning knob and that the frequency display should be updated.

 

Si4844-A10 Programming

Essentially, the Arduino sends the radio chip commands over the I2C bus and the radio chip subsequently replies to the commands by performing the requested action and returning status information. The Si chip can operate in several modes and some make it possible to configure some very detailed radio bands and properties. In this project, we are using the Si4844-A10 chip in a mode that accepts pre-defined or default radio bands with default properties. This mode was chosen because it easily accommodates a great deal of basic functionality while still offering a degree of customization.

Rather than simply setting an AM/FM/SW “register”, the radio chip can be set to one of 41 different frequency bands. Bands 0-19 are FM, 87-109 mHz; bands 20-24 are AM, 504-1750 kHz; bands 25-40 are SW, 5.6-22.0 mHz. The bands, however, do not have simple equal-interval spacing, which might make tuning cumbersome. Instead, the frequency range of many of the bands are the same or differ only slightly, but with differing properties, such as de-emphasis (FM) or channel space (AM), stereo separation (FM) and RSSI thresholds. Consultation with the referenced datasheets and application notes is necessary to completely understand this scheme and you will see some clear tables for the bands as well as all of the modes, programming commands, and the status and reply formats.

In this project, the included software will enable access to all of the default bands as well as controlling basic properties including mode changes (AM/FM/SW), volume, tone, and mute.

 

Add a Keypad

To control the radio, we need an input device. A simple membrane keyboard as pictured is sufficient for our purposes. These have been around for a while and are easy to interface with an Arduino. While I have illustrated the row and column orientation for the one that I used, you should verify that yours is the same.

 

Membrane Keypad

Simple membrane keypad

 

Keypad Arduino

Keypad to Arduino connections:

Row 1 D8
Row 2 D9
Row 3 D10
Row 4 D11
Col 1 D13
Col 2 D14
Col 3 D15

 

For keypad software, I used the library from Mark Stanley and Alexander Brevig which is released under the GNU General Public License. For the project, we will map functions to the keys as illustrated below.

 

Keypad mapping

Keypad mapping for the radio functions

Keypad Function Definitions:

  • AM : Switch to AM mode, band 22
  • FM : Switch to FM mode, band 8
  • SW : Switch to SW mode, band 31

Note that the default bands under the mode changes are configured in software and are easy to modify. Additionally, the current volume and tone values will be carried over in the new mode.

  • Vol+ / Vol- : Increase or decrease the volume by one step. There are 64 levels of volume. Because of the use of amplified speakers in the project, these are not so essential but are still nice to have.
  • Band+/Band- : Increase or decrease the band by one step, but within the available bands in the current mode.
  • B/T+ / B/T- : Increase or decrease the tone by one step. I admit that I am being somewhat liberal in my use of the term “tone”. For the FM mode, this will increase or decrease the bass / treble level from 0 (max bass) to 8 (max treble). For the AM/SW bands, this will set a channel filter from 1-7. The filters are at 1.0 kHz, 1.8 kHz, 2.0 kHz, 2.5 kHz, 2.83 kHz, 4.0 kHz, and 6.0 kHz, respectively. Note also that for simplicity and programming convenience (i.e., laziness), levels of 0/1 and 7/8 can be made in AM/SW mode, but do not differ.
  • Mute: Toggles audio output on and off.

 

Add a Display

With the input device set up, we need to be able to display the settings of the radio. I can think of no better screen to use with this project than one from the old Nokia 5110/3310 cell phones. I had a well-used one of these around (see pictured) and their old-school charm seems particularly appropriate.

 

Nolia Display

Nokia display

 

There are two important points to consider when interfacing this display. First, there are several varieties of these displays available and they can have different pinouts. You should verify the pin connections on yours to make certain that it is, in fact, a 3.3v device and that it is attached to the Arduino Pro Mini correctly. Second, because all of the I/O on the Arduino used in this project is 3.3v, I did not have to use the dropping resistors that you usually see when these screens are used with 5v flavors of Arduinos, like the UNO.

 

Display Pin / Function Arduino / Circuit
1-RST D3
2-CE D4
3-DC D5
4-DIN D6
5-CLK D7
6-VCC Vcc (3.3v)
7-LIGHT GND
8-GND GND

 

For software, I chose to use the LCD5110_Basic library available under the CreativeCommons license. This library is mature, very easy to use, and fast.

Pictured below is the populated radio display in use:

 

Radio display

Radio display in use

 

Starting from the top left, we display:

                    Row 1- Mode (AM/FM/SW) and the band number

                    Row 2- Band frequency range

                    Row 3- Volume and base/treble levels

                    Row 4- Current frequency (mHz or kHz)

                    Row 5- Stereo indicator (FM only) and mute (if on) 

Of course, this information is constantly updated to represent changes from tuning or keyboard input.

 

The Completed Radio

Depicted below is the assembled project on a breadboard – perhaps not as neat as it could be (ok, it’s a mess), but completely functional. Certainly the performance can only improve by a more permanent layout.

 

Project Breadboard

The completed radio on a breadboard

 

The software to run the radio is available for download below. It is liberally commented and is, hopefully, both easy to understand and easy to modify, if desired. The main loop in the software is straightforward. It 1) checks and displays any change in the tuner frequency and 2) checks if a keypress has been made and, if so, executes the appropriate command. The rest of the program consists of all of the supporting functions.

I am very impressed by the reception that the circuit is able to achieve right on the breadboard. FM is very good. AM is good and I am able to get quite a few SW broadcasts. Nevertheless, reception can, undoubtedly, be increased through the use of specialized antennas.  

 

Closing Thoughts

This has been a challenging and enjoyable project. I am definitely impressed by the Si4844-A10 chip. There is a great deal of capability packed into a single chip and that always amazes me. I feel like I have only touched on the possibilities— but, hopefully, this project can serve as a foundation if you are interested in experimenting.

 

Code

Download the software for the project here:

 

  Download Code  


Comments

10 Comments


  • Erik Burman 2016-06-13

    You BOM doesn’t specify which parts are SMT and which are through hole. It’s difficult to make out all the detail in your breadboarded circuit photo. There are two boards at the top of the photo each with SMT parts. I’m guessing that they are part of the antenna circuits?  Can you please clarify? Also, what crystal did you use for Y1? There’s lots of possible choices. Can you tell me which part number you used (Digikey or Mouser)? Thank you.

    • Raymond Genovese 2016-06-14

      Hi, I used four SMTs on the project as follows (schematic name, description, Mouser part number):

      L1, 270 nH (.27uH) Inductor, 652-CS160808-R27K
      B1, ferrite bead 2.5 kOhm (100 mHz), 81-BLM18BD252SZ1D
      C12 and C14, 33 nf non polarized capacitor, 603-CC805KRX7R9BB333

      The crystal I used:
      Y1, 32.768 kHz crystal, 732-C002RX32.76K-EPB

      Hope this helps and, if you do build the project or something similar, please let me know how it went for you - I always like to hear about that, including any improvements. - RFG

      • Erik Burman 2016-06-14

        Thanks! That helps a lot! I’ll let you know how it all works out. Although, now I’m considering just getting the SI4844-B-DEMO demo board through Digikey. It’s not very expensive. Or maybe I’ll try doing both. Silly me!

  • keepitsimplestupid 2016-06-14

    Your units are a bit off 87.5 mHz is mill-Hertz.  MHz is Mega-Hertz.  Proper names generally capitalized.

    m=milli, M=Mega

    Cool though.

  • Aviv Weinstein 2016-06-25

    Hey Raymond,

    I am attempting to re-create this project and I have a few questions I was hoping you could answer.

    1) How did you make your whip and ferrite antennas? Is there an online guide you recommend following? I do not know what you mean/meant when you say you took an old antenna from an AM/FM radio.
    2) From which vendor did you order the Si4844 A-10 from? All vendors I have found offering this chip have lead times of a month or longer.
    3) Looking back at building this circuit, do you have any general tips to someone trying to rebuild it?

    • Raymond Genovese 2016-06-26

      Hi,
      The telescopic/whip antenna that I used was from my junk box - usual kind of collapsible antenna that you find on so many radios. If you search for “telescopic antenna” you will see plenty of pictures of these. The one I am using has an extended length of maybe 20” or so.

      People do make their own ferrite antennas and if you search for “ferrite antenna” there is plenty of material. I reclaimed one from a “discarded” radio. The one I used that you see pictured is pretty cheap. If you look at Si’s design guide that I linked to in the article, they provide information on the kinds of ferrites that they recommend (p. 29). I also saw these available online for sale, but I was able to get a very used, beat up radio at a thrift shop locally for only a few bucks, so I went that way on a gamble and it worked out.

      I purchased the chip from either Mouser or Digikey (I can’t remember at the moment but it was definitely one of the two) and you are absolutely right, both are currently out of stock (I just looked), but they both say that they are on order. You might be able to find one somewhere else, but I don’t know where, off hand.

      A general tip looking back? Well, if it interests you then go for it! I was amazed that it all works well and I was listening to it this morning. I am also confident that someone else can not only build it, but improve on the design. I’m also a little embarrassed to say that it is still on the breadboard smile

      Hope this helps.

      • Aviv Weinstein 2016-06-30

        Hey Raymond,

        Thanks a million for the informational reply! I am interested in this project as it seems like a fun thing to try. I’ve ordered the parts you recommended in this article and I will attempt to get a “large scale” version of this radio put together and in working order. With a working system, I will then attempt to design as PCB for this circuit and its peripherals and see if I can make a portable version of this.

  • can i use Arduino Uno R3 with SI4448-A10 instead of Arduino Pro Mini ?

    • Raymond Genovese 2016-10-24

      It is not impossible but not really advisable in my opinion. A big issue is that the UNO is a 5v board with 5v I2C. The SI4448-A10 is 2-3.6v.