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Blog Building a Simple Radio Receiver
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  • Author Author: shabaz
  • Date Created: 26 Jun 2021 3:34 PM Date Created
  • Views 14207 views
  • Likes 13 likes
  • Comments 7 comments
  • silabs
  • silicon labs
  • fm receiver
  • radio
  • beginners
  • rf
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Building a Simple Radio Receiver

shabaz
shabaz
26 Jun 2021

  • Introduction
  • Radio Circuit
  • Amplifier Circuit
  • Power Entry
  • Circuit Board
  • Wiring Diagram
  • Soldering
  • Enclosure
  • Components and Parts List
    • Potentiometers
    • Speaker
    • Parts List
  • Summary

 

Introduction

The aim of this project was to design a simple radio receiver that anyone could assemble by deliberately using large surface-mount components.

image

 

The final design is very low-cost (approx. £20 GBP or $25 USD not including the speaker, but the cost reduces to perhaps half of that if assembling several of them, due to minimum order quantities of some parts), and normal soldering tools can be used to assemble the circuit. It can be fully constructed within a few hours. There is no circuit adjustment or trimming needed, and the prototype worked the first time – it's very easy to have a successful result the first time with this project.

 

There is a 3-minute video explanation and demo of it here:

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image

 

I'm convinced that children could assemble this circuit. After watching sub-10-year-olds soldering a couple of surface-mount integrated circuits (see photos below), I was encouraged that surface-mount technology was not difficult for them! If anything, occasionally through-hole components posed more of a problem.

 

Of course, to solder surface-mount successfully they had to use a reasonably small soldering tip size (around 1 mm) and thin solder (0.38 mm diameter is great) and some of the components had to be taped into position, or Blu-Tack (repositionable putty) can come in handy.

image

 

Working in pairs, it should be possible for one child to hold a surface-mount component in position with tweezers, while the other solders it.

 

image

 

Radio Circuit

The radio circuit is based around a single integrated circuit (IC), Silicon Labs SI4825, and not much else. The SI4825 accepts a variable resistor (potentiometer) to act as the tuning control.

 

The circuit is shown below. The FM antenna input is pin 1 on connector J3 on the far left side of the circuit. Pins 2 and 3 on that connector are for AM mode, which isn't implemented.

image

 

 

The right-side portion of the circuit consists of a string of resistors that are used to select the desired frequency band and mode. There is a chain of resistors to select the frequency band, the idea being that a multi-way switch can be used to select a tap point between resistors. In my case, I decided to not connect any switch there and I soldered a wire jumper to permanently select the FM broadcast band.

 

By changing the resistor values, or by moving the wire jumper or wiring a switch there, the SI4825 can be reconfigured to support AM broadcast and short-wave modes, or different region FM bands. The circuit diagram and the circuit board are labeled with the wire jumper position to select the FM band for Europe or the USA region (for other regions, the SI4825 datasheet will need to be examined).

 

Tuning is achieved by adjusting the potentiometer VR1, and the audio appears on pin 16 of the IC. An antenna wire is soldered to pin 1 of connector J3. The circuit is powered from 3V, so two AA or AAA batteries can be used. The circuit diagram shown here forms the entire radio apart from the audio amplifier! It's impressive how few components are needed.

 

Amplifier Circuit

The circuit below forms the audio amplifier that connects to the audio output pin from the radio chip. The audio can be adjusted for volume using the potentiometer VR2 shown on the left side of the circuit below. The audio is amplified/converted to differential signals using the transistor Q1. The integrated circuit U2 is an audio amplifier chip to drive the 8-ohm speaker.

image

 

Power Entry

A 3V battery (two AA cells) connected to J4 is used to light an LED and provide power to the rest of the circuit.

image

 

Circuit Board

The PCB files are attached to this blog post. Large 0805-sized surface-mount components are used for ease of assembly. In terms of layout, the top half of the circuit board contains the radio circuitry. The lower half contains the audio amplifier. The right side of the board is a detachable portion containing just the power entry part of the circuit. The idea was that depending on the particular enclosure, it may be desirable to place the switch and LED in a different location, and in that case, the power entry part of the board can be separated and extended with a couple of wires.

image

image

 

The completed board is shown in the photo below. It's quite quick to solder. The yellow wire acts as the FM antenna. The twisted black wires go to a 2-inch diameter 8-ohm speaker. The power wires on the right side attach to the 2xAA battery holder.

image

 

Wiring Diagram

The diagram below shows the required connections. The region selection wire is shown in the Europe position (shorting pins 1 and 2) but for the USA region, pins 1 and 3 need to be shorted instead.

image

 

If the power switch and power LED are separated from the remainder, then two wires are used to electrically connect them as shown above.

 

Soldering

The general procedure I use is to solder in all the smaller components first, particularly the resistors, and then the capacitors. Once all the smaller parts have been soldered in, then the transistor, the crystal, and the two ICs can be soldered in. All the through-hole parts are soldered last.

 

Enclosure

The dimensions of the circuit board are shown below. This is from the component side of the board, so it needs to be flipped around if it will be used to mark out a panel from the front side. The hole diameters required on the front panel for the power switch and the potentiometers depend on the specific parts used.

image

 

I plan to use a sweets tin and secured the circuit board inside using epoxy resin glue (alternatively a 3D printer could be used to create brackets or an entire enclosure).

See Building a Simple Radio - Part 2 - Final Assembly

image

 

Components and Parts List

Most of the parts are available from Farnell. Resistors R2 to R9 need to be 1% tolerance, these are low-cost 'thick film' parts. See the parts list below.

 

Potentiometers

I used potentiometers from Aliexpress, but I later found that Farnell has the correct sized ones too, at a low cost. The Aliexpress search term is WH148 and there are lots of online stores selling them. These potentiometers are available in different heights, and the circuit board is compatible with 12.5 and 15 mm versions (20 mm may be hackable into place). The volume potentiometer should preferably be a log type, but the tuning potentiometer must be linear type. The precise values are not important, but 10k is a good ballpark for the volume potentiometer, and 100k to 500k will work for the tuning potentiometer (I used 100k).

 

The knobs for the potentiometers were also from Aliexpress.

 

Speaker

I used an 8-ohm speaker from Aliexpress, 2-inch diameter.

 

Parts List

The list below does not include the speaker (8 ohms), and knobs (6mm serrated), and enclosure. All resistors are 1% thick film.

 

The parts are listed in the preferred order of soldering (i.e. smallest parts first).

 

#Mnfr CodeDescriptionIdentifierQty
1MCWR08X1003FTLMCWR08X1003FTL100k 0805R11
2MCWR08X4702FTLMCWR08X4702FTL47k 0805R21
3MCWF08P1002FTLMCWF08P1002FTL10k 0805R3, R4, R5, R64
4RK73H2ATTD3903F.RK73H2ATTD3903F.390k 0805R71
5MCWR08X2202FTLMCWR08X2202FTL22k 0805R8, R102
6MCWR08X1001FTLMCWR08X1001FTL1k 0805R91
7MCWR08X2702FTLMCWR08X2702FTL27k 0805R111
8MCWR08X2201FTLMCWR08X2201FTL2.2k 0805R12, R132
9ERJ6GEY0R00VERJ6GEY0R00V0R 0805R14, R152
10ERJ6ENF1000VERJ6ENF1000V100R 0805R16, R172
11MMZ2012S601AT000MMZ2012S601AT000FBEAD 0805FB1, FB2, FB3, FB44
12MC0805B104K101CTMC0805B104K101CT100nF 0805C1, C2, C93
13C0805C220J5GACTUC0805C220J5GACTU22pF 0805C3, C42
14C2012X7R1E475K125ABC2012X7R1E475K125AB4.7uF 0805C5, C6, C153
15CC0805KRX7R7BB224CC0805KRX7R7BB224220nF 0805C7, C82
16C0805C221K5GACTUC0805C221K5GACTU220pF 0805C11, C122
17GRM21BR61A226ME51LGRM21BR61A226ME51L22uF 0805C131
18X32K768L104X32K768L10432.768kHzX11
19BAV99BAV99BAV99D11
20BC849BLT1GBC849BLT1GBC849BQ11
21SI4825-A10-CSRSI4825-A10-CSRSI4825U11
22PAM8302AADCRPAM8302AADCRPAM8302U21
2316SVPC100M16SVPC100M100uF 16VC101
24P160KNP-0QC20B100KP160KNP-0QC20B100K100k Lin PotVR11
25P160KNP-0QC20A10KP160KNP-0QC20A10K10k Log PotVR21
26PVA1 EE H1 3.5N V2PVA1 EE H1 3.5N V2SwitchSW11
27L-53LYDL-53LYDLED YellowD21
28MP000329MP0003292xAA Batt HolderJ41

 

 

Summary

With little work, it is possible to make a usable radio with the Silicon Labs SI4825 chip. As mentioned, due to the simplicity it worked first time. The sound quality is similar to any typical portable radio. I think this could be a reasonable project for young children to work on, with a little supervision.

 

Thanks for reading!

Attachments:
export-radio-v1.zip
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Top Comments

  • rsjawale24
    rsjawale24 over 3 years ago +2
    A neat and clean PCB design with clear instructions. I have always wanted to create my own radio receiver from scratch. This one seems like a good start. Have you considered making a transmitter too?
  • shabaz
    shabaz over 3 years ago in reply to rsjawale24 +2
    Hi Rushiraj, Thanks! Transmitters are more problematic, due to different laws in different countries. For audio broadcast stuff at very low power, there are some all-in-one ICs intended for converting…
  • DAB
    DAB over 3 years ago +2
    Nice project. DAB
  • bcschmi
    bcschmi over 3 years ago

    Hi Shabaz, 

    For the amplifier side of the circuit, could the output from the Si4825 be connected directly to the input on the PAM8302 without the transistor (with the input negative connected to gnd)? What is the benefit of differentiating and amplifying the signal first? Thanks

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  • shabaz
    shabaz over 3 years ago in reply to bcschmi

    Hi Ben,

     

    C13 and R16 together form a low-pass filter for the power supply, I placed that in case the PAM chip produced any noise. You can run it with 3.3V, without needing to change things. I think the difference in voltage is small enough that it won't affect anything (also, 2 x AA Alkaline cells product about 3.2V when fresh anyway, and that worked fine).

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  • bcschmi
    bcschmi over 3 years ago

    Hi Shabaz,

     

    I have a few questions about the amplifier circuit.

     

    1. What is the purpose of C13 above the collector pin on the transistor?

    2. What is the purpose of R16?

    3. could I supply 3.3v instead of 3v to the transistor part of the amplifier? Is that enough of a voltage change to require new values for the collector, emitter, and voltage divider resistors? Thanks,

     

    Ben

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  • genebren
    genebren over 3 years ago

    A very nice design (clear and simple).  This would be a great project for anyone wanting to discover more about electronics, while building a useful radio.

     

    Well done.  (I am not sure how I missed this blog when it was originally posted)

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  • DAB
    DAB over 3 years ago

    Nice project.

     


    DAB

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