Minimal RPItalk Configuration

Introduction

This page describes the minimal hardware and software configuration needed to build a working RPItalk system. The goal is to create a simple, reliable speech synthesizer using a Raspberry Pi that can be connected to a host computer and used with a screen reader.

This configuration is intended for users who want a dedicated speech device similar in function to older hardware speech synthesizers. The Raspberry Pi runs the speech software and communicates with the host computer over a USB serial connection using USB gadget mode.

Using USB gadget mode is the least expensive way to build an RPItalk synthesizer because it uses an inexpensive Raspberry Pi Zero 2 W and a standard USB cable that you may already own. The Raspberry Pi can also be powered directly from the host computer over the gadget connection, so a separate power supply is not strictly required.

Hardware Instructions

1. Acquire Hardware

   The following hardware is recommended:
   • Raspberry Pi Zero 2 W with headers installed
   • Pimoroni PIM485 audio HAT
   • MicroSD card
   • Standard USB-A to mini-USB-B data cable (must support data, not power-only)
   • Optional case
   • Optional Raspberry Pi power supply

2. Learn the Raspberry Pi Zero 2 W Configuration

   To understand the Raspberry Pi Zero 2 W Orientation and Ports, do the following:
   Hold the Raspberry Pi Zero 2 W so that the USB ports are facing you.
   The ports, from left to right, are:
   
   • Mini HDMI
   • USB OTG (mini-USB-B)
   • Power
   The microSD card slot is located on the top-left edge of the Pi. The 40-pin header is along the top back edge. Unlike some other Raspberry Pi models, there are no ports or features on the bottom of the Zero 2 W.

3. Install the PIM485 HAT

   To install the PIM485 HAT onto the Raspberry Pi Zero 2 W, align the header block on the PIM485 HAT with the 40-pin header on the Pi.
   Press down firmly until the HAT is fully seated.
   Moderate pressure may be required.

Software Instructions

1. Flash the microSD card with Raspberry Pi OS

   You may use the full version of Raspberry Pi OS, but Raspberry Pi OS Lite is sufficient.
   Download Raspberry Pi OS from: Raspberry Pi OS downloads

2. Enable gadget mode on your Raspberry Pi

   This requires editing two files on the boot partition of the SD card:
   • cmdline.txt
   • config.txt
   
   The file cmdline.txt always consists of exactly one line. Add the string modules-load=dwc2 to the end of the line. Make sure you do not add a second line. You can download an example cmdline.txt file here.
   Next, add the line dtoverlay=dwc2 to the end of your config.txt file after the [all] section tag.

   [all]
   dtoverlay=dwc2
   

   You can download a sample config.txt file here.

3. Enable the PIM485

   Add the following lines to your config.txt file to enable the PIM485 audio HAT:

   # Enable Pimoroni PIM485 audio
   gpio=25=op,dh
   dtoverlay=hifiberry-dac
   

4. Optional: Configure network

   Optional but highly recommended. Configure networking and enable SSH access before the first boot. This makes setup and troubleshooting much easier.

5. Install the rpitalk package

   Boot the Raspberry Pi and log in.
   Install the rpitalk package by following the instructions on the main RPItalk page: RPItalk Installation Instructions

Questions or corrections: jheim@math.wisc.edu

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