P08027: Wireless Assistive Control System


Table of Contents

This section discusses the audio system implemented to provide audible feedback to the user.


The RC car has a speaker and ISD1700 series (Chipcorder) IC installed to produce audible feedback to the user. These sounds will indicate the direction of travel in the forward/reverse and left/right directions. The ISD17240 IC was stores the sampled audio and is instructed by the vehicle's microprocessor to play sound effects dependent upon the user's actions.



Chipcorder Circuit

Chipcorder Circuit

The chipcorder has two modes of operation:

These modes of operation were both used in the development of the audio subsystem.

Recording Audio

Audio recordings utilized the pushbutton mode of operation.

In order to record sound onto the chip, the feed through (FT) button and the record (rec) button must be pulled low. Then LED1 will turn on to show that the chip is recording. When the play pin is pulled low, the chip will then play the last recorded sound. The forward button is used to change from tack to tack for both recording and playing. Erase is used to erase the current track and then reset is used to perform a global reset, erasing all saved data on the chip. A global reset is the only way for the chip to recover from an error state. If the chip receives a command while in the middle of another command, it will ignore the data.

Audio Playback

Set_Play Command Sequence

Set_Play Command Sequence

Audio playback is was implemented through the use of the SPI interface. SPI communications are enabled in the microprocessor's Universal Serial Interface (USI). The USI is configured to operate in three wire (SPI) mode. Periodically the microprocessor sends a command to the chipcorder through the SPI bus. These commands instruct the chip corder to play the audio recorded within the device for a certain block of memory. In doing so the car is constantly producing audible feedback which indicates the direction of travel.

The figure to the right roughly outlines the procedure necessary to send data through SPI to the chipcorder and produce sound. The design reference outlines data communications, although there are some discrepancies within the PDF.[1]

The typical communication takes place as follows:

  1. Issue the Power UP (PU) instruction
  2. Clear interrupts
  3. Issue a Set_Play instruction followed by the start and end memory address' of the message to be played
  4. Clear interrupts
MOSI Message Format

MOSI Message Format

Messages formats and instruction variable requirements are defined in the design reference document. They are typically of the format illustrated in the figure above.

Note: All data communications are transmitted least significant bit first!

Audio Tracks

The sounds used on the car are a "vroom" sound starts moving either forward or reverse, a rumble noise is used as an idle sound, and a "screech" noise is made when turning left or right. The sounds were recorded using the software Audacity and were transmitted to the chip via a mini cable (1/8 inch) connected to the computer's speaker port and the AnaIn pin on the chip. An 8 ohm, 1 W speaker was used.


  1. ISD1700 Series Design Guide