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Talking Toaster

Project Update 1

Corin Anderson & Chris Setter

CSE 477, Spring 1996


Our project is to design and build a toaster for the Computer Scientist. It's main features will include a voice response system, heat and other sensors for monitoring toast making, and self-actuating bread platform. The user may easily select toast quality from a control panel, and can be assured of a correctly prepared slice every time.

On first glance, the toaster will look like a toaster of the classic 1950's era, complete with polished aluminum sides and traditional toasting lever. Inside, however, is a completely different story. Internal to the toaster will be a microcontroller that will process the sensor input and generate appropriate responses.

Sensors will include ToastHungryPerson proximity sensing, BurntToastCondition detection, and HeatAbsorption measuring. As for user interface, there will be speech recognition and voice response. Further, the speech recognition will be speaker-dependent, so toast can be made custom to multiple users.

To ensure the safety of the ToastHungryPerson, the toaster will be built to properly insulate the line current that is used by the heating coils. Additionally, to ensure the safety of the toaster, the microcontroller will be shielded from the line current switch by external circuitry, such as a transistor.


With the exception of a few sensors, all the major components of our project have been acquired. The most costly components are the voice playback IC ($15), voice recognition IC ($32), power relay ($15), and microcontroller ($25). An estimate on the total cost of the project would be $100.


Our design lends itself easily to modularity. Each major component of the toaster is its own module, and can be tested independently of all other modules. Below is a list of the modules in the toaster and experiments to learn more about each. The schedule for these experiments is listed in Appendix B.

Voice Playback
The voice playback module is based on the ISD1000A sound chip. This chip is a standard part used by many CSE 477 projects in this and past quarters, so the design is well known. To test this design, we will implement the circuit described in the ISD1000A's literature. This test circuit will also serve as a platform for recording our voice responses for the toaster.

Voice Recognition
The voice recognition module is designed around the HM2007 speech recognition chip. Like the voice playback circuit, a test circuit will be breadboarded for the voice recognition module. Unlike the voice playback circuit, however, our project is the first project to use a speech recognition chip, so we cannot rely on past experience to help guide us. Fortunately, the documentation that came with the chip, although not always as lucid as it could be, does provide adequate diagrams and a sample circuit that can be used as the basis for the recognition module.

Heat Sensor
The heat sensor we have selected is an Analog Devices 590JH. It can withstand temperatures up to 300°F. With this constraint in mind, we will conduct several tests to determine the best mounting place for this sensor. There is a balance between keeping the sensor within its heat tolerance and placing the sensor where it can be most reliable. Using a thermocouple, we will measure the heat produced by the toaster at various locations to determine the "safe" areas.

Proximity Sensor
To detect the presence of Toast-Hungry person, we will use a pyrometer. The pyrometer is one of the components that has not been acquired yet, but will be in the next week. Once the sensor has been obtained, a small circuit will be constructed to determine the behavior of the device.

Bread Sensor
There are a few possible methods for detecting bread in the toaster. One is to use an LED emitter and detector pair. The beam of light would be broken by the toast. The advantage with this system is reliability. The disadvantage is that the LEDs may not be able to withstand the extreme heat of the toaster.

Another method is to use two photoresistors, one inside the toaster, one outside. The interior detector would detect how much ambient light from the room is trickling into the toaster. When bread is in the toaster, the ambient light would be blocked. The exterior detector would determine how much light is in the room to begin with. That is, if the lights in the room are turned off, there won't be any light in the toaster, with or without bread. The advantage of this system is that the photoresistors may be placed farther from the heating coils and bread than the LEDs would be placed.

Smoke Sensor
To detect smoke in the toaster, a matched emitter-detector pair of LEDs will be used. We will be conducting tests on this system to determine if the LEDs can withstand the heat produced by the toaster.

Construction and Debugging Plan

All the electronics for the toaster will be housed in a case underneath the toaster. The controlling logic will interface to the toaster and its sensors through a modular plug so the toaster and case may be separated. This will ease the debugging of the design as well as the robustness of the entire unit.

There are four major stages of this project. As specified, they may be implemented in parallel between Chris and Corey. The stages are:

Voice Interface System (VIS)
The VIS consists of the voice playback module and the voice recognition module. After the experiments for these modules, they will be assembled onto either wirewrap or solder boards. Modular plugs will be included so the microphone and speaker may be attached later. Easy access to the control, data, and address lines will also be included to ease debugging in the final design. The VIS will be mounted inside the case.

Sensor and Devices System (SDS)
The SDS includes all the sensors and actuators in the project. After experiments are conducted with each sensor and actuator, the device can be mounted inside the toaster. Wires will be placed carefully in the toaster to reduce heat effects from the toasting coils.

Toaster Operating System (TOS)
The TOS will be developed concurrently with the experimentation of the modules. As code is debugged for each module, it will be added to the operating system of the toaster. When the experimentation is finished, the TOS should be mostly complete as well.

Debugging the design
It would be foolish to claim that the toaster will work properly from the start. As such, we will provide debugging hooks in both the software and in the hardware implementation. In software, we will take care to document the system as we develop it. This document can serve as a road map for debugging the microcontroller code. On the hardware side, easy access to control, address, and data lines will be provided. These signals will be labeled in the circuit so that they may be easily traced.

Appendix A

Initial Design Schematics

Level Schematic]

High level design schematic.

Appendix B

Division of Labor and Schedule

The tasks of the project lend themselves to parallelization without much difficulty. The following table summarizes the activities we each will be doing in the upcoming few weeks.

Week of          Corin Anderson Chris Setter
May 6
(Week 7)
Experiment with voice playback circuit. Begin experimenting with voice recognition chip. Clean up toaster.
May 13
(Week 8)
Conclude experiments with voice recognition chip. Begin laying out microcontroller code for TOS. Begin experimenting with proximity sensor. Experiment and install heat sensor. Experiment and begin implementing a bread platform mechanism. Determine which smoke and bread sensors we will use.
May 20
(Week 9)
Do final assembly of VIS on wirewrap or solder board. Continue writing TOS. Record voice responses for toaster. Finish experimenting with proximity sensor. Experiment and mount bread and smoke sensors. Determine interface method between toaster and electronics case. Finalize implementation for bread platform. Merge sensor input code with TOS.
May 27
(Week 10)
Mount proximity sensor. Help Chris with sensor mounting in toaster. General debugging. Mount power supply and heating coil switch. General toaster hardware maintenance.
June 3
(Week 11)
Write final report, hope that nothing breaks. Write final report, hope that nothing breaks.

Corin Anderson |
Last modified: September 8, 1996