ScoutAM

Scout-Radio

Si4732 and Raspberry Pi Pico Radio device for Scouts to build and use to gain badges

Reading and District Amateur Radio Club works withl local Scouts groups and help them in support of their badges and activities

Objectives:

• Design and build a radio device with can support Scouts in the following badges
  • [Electronics](https://www.scouts.org.uk/scouts/activity-badges/electronics/)
  • [Communicator](https://www.scouts.org.uk/scouts/activity-badges/communicator/)
• Involve Scouts in radio activities
• Potential Sponsorship and incresaed local community technology support for Scouts
• Interesting Project for RADARC Constructors
• Have Fun!

Design Specification

Derived from the RLab Reading Hackspace Project Athena

• Microprocessor design based on Raspberry Pi Pico Microcontroller
• Programmable firmware in CircuitPython and other programming languages via USB
• On Board AM and FM Radio
• Loudspeaker and audio output
• Rotary Encoder and control buttons
• Battery powered 3 off AAA, or LiPo with on board charger from USB
• Audio output jack
• Mixture of surface mount and through hole components. Some components can be factory assembled
• Colour LCD display integral
• Optional GPS module
• Optional Compass module
• Low Cost, under £20

Proposed Design

The following elements are in the prototype design, being commonly available at reasonable cost. Some of these may not be in the final design or optional modules to save cost:

Raspberry Pi Pico Processor Module

The Raspberry Pi Pico module is based on the RP2040 microprocessor. The module includes flash memory, power supply, crystal clock and a USB interface. It is an easy way to to integrate this processor without detail PCB layout and at attractive cost. The Pi Pico Module have different variants which are pin compatible. They offer different USB Connectors(Micro-B, USB-C), Wireless and bluetooth integrated, and a higher performance version in the RP2350. Pi Pico Data sheet

The RP2040 is an ARM Cortex M0+ 32 bit processor which operates at 133MHz and includes a wide range of integrated peripherals. RP2040 Data sheet

High quality software support for the RP2040 and Pi Pico Modules is available in C/C++ (C SDK, and Arduino Pi Pico), and Python(Micropython, and CircuitPython)

SiLabs Si4732 AM/FM radio

Datasheet

The Si4732 is an integrated AM/FM radio device which is digitally programmable over I2C. It covers a range of frequencies:

• Worldwide FM band support (64–108 MHz)
• Worldwide AM band support (520–1710 kHz)
• SW band support (2.3–26.1 MHz)
• LW band support (153–279 kHz)

The radio also supports FM stereo and RDS. Software patches are available for the device to support SSB and NBFM

Rotary Encoder and push button controls

A side operated rotary encoder is installed on the prototype, but we might look at lower cost alternatives. There are 6 tactile push button switches which can be used to invoke the various radio functions. These controls can also be used to play simple nintendo like games on the radio.

Audio Output

The stereo audio audio output from the radio chip is amplified to provide an output to headphones of external speakers. This is then further amplified to drive an on board loudspeaker. The output from the radio chip is also fed to the ADC inputs on the Pi Pico to enable the Pi Pico to provide USB or Bluetooth feed to an external program such as WSJT-X. The Pi Pico may be able to decode locally digital protocols such as FT8 and display locally. The Pi Pico also provides a PWM audio output for beeps, morse code, and music for simple games.

1.3 inch IPS Colour LCD Display

A colour LCD display was chosen for the device. Limited space allows for a 240 by 240 pixel 1.3 inch IPS display. The module is based on the ST7789 display IC and is supported by both Micropython and CircuitPython grahics libraries.

Torch

A high intensity white LED is provided under processor control to be used as a torch or for visual signalling.

Compass Option

An optional compass module based on the LSM303 magnetometer, Compass and accelerometer device can be fitted.

GPS Option

An optional GPS module based on the ATGM336H GPS receiver can be fitted

Costs

The following costs are based on the JLCPCB prototype build of five units. All costs are in UK pounds and include shipping and taxes

Component Costs

The above component cost includes PCB, SMT components, Pi Pico, display and all switches and connectors. I does not include a case. The placed components were placed by JLCPCB. This cost is dominated by the radio chip and rotary encoder, better sourcing could easily get the component cost under £15.

Optional Components

Build Costs

The build costs are again based on the five off prototype, so maybe not very representative of a larger batch. I excluded from the build the through hole components to save cost, also a couple of components that they did not have in stock. Build costs are driven by a mix of fixed costs per order, setup, solder stencil, etc. Also Costs per board and joint.There are then costs related to what components are used. Common components are already mounted on the pick and place machine and have low cost per component ( fraction of cent). Less common components are often low cost, but we pay $3 per component type to load the component spool to the pick and place, this cost often dominates the assembly costs. Assembly of through hole components and components and edge mounted components is possible but would attract increased cost.

For the five prototypes:

The placed component costs can be excluded, so $44.32 for five. With tax and shipping this is £11.08 per board. Rather expensive at prototype level, but for for a decent board volume (25) when I run through the pricing calculator I get £2.20 per board.

PCB Files

Installing Software

reinstallsys.sh installs a system from scratch including Circuit Python. Runs on linux only atm.

Software Project Plan, 12th March 2025.

Tasks are either small, medium or large (S/M/L)

In priority order:

• Sort out test code and harness for si4735 driver (done)
• Design and implement a software installation process for target hardware, automating wherever possible (M, done)
• Document possible use cases (M)
• Provide example higher level libraries and applications (M)
• Design and implement standalone POST/BIST for target hardware (M)
• Design and implement production test software. Possibly involves use of laptop. Scouts need to know if what they have built works :-) (M)