Reviving the Heathkit Hero Junior with Votrax SC-01A Synthesizer
Table of Contents
- Introduction
- Replacing Modern Electronics
- Adding the Original Votrax SC01A Speech Synthesizer
- Designing the Speech Synthesizer Board
- 4.1 The Microcontroller
- 4.2 The Speech Circuitry
- 4.3 Power Supply
- 4.4 RS232
- Inputs and Outputs
- 5.1 Phoneme Inputs
- 5.2 Inflection Inputs
- 5.3 Strobe Signal
- 5.4 Feedback
- 5.5 Audio Signal
- 5.6 CB Line
- Choosing an Amplifier Board
- Voltage Issues
- 7.1 Boost Converter
- 7.2 Adding Fuses and TVS Diodes
- Troubleshooting and Bug Fixes
- Demonstration
- Conclusion
Replacing Modern Electronics with the Votrax SC01A Speech Synthesizer
In this article, we will explore the process of replacing modern electronics in the Hero Jr robot with the original Votrax SC01A speech synthesizer. We will Delve into the design of the speech synthesizer board and discuss the various inputs and outputs involved. Additionally, we will address the voltage issues and provide troubleshooting tips for any problems that may arise along the way. Finally, we will conclude with a demonstration of the completed speech board in the Hero Jr robot.
Introduction
The Hero Jr robot is a classic toy that originally lacked any speech capabilities. In previous videos, we have demonstrated how to upgrade the robot with modern electronics. However, in this project, We Are taking a different approach by adding the original Votrax SC01A speech synthesizer to maintain the robot's authentic sound.
Replacing Modern Electronics
Before diving into the process of adding the Votrax SC01A speech synthesizer, it is essential to understand the previous upgrades made to the Hero Jr robot. By replacing the outdated electronics with modern components, the robot's functionality and capabilities were enhanced.
Adding the Original Votrax SC01A Speech Synthesizer
The Votrax SC01A speech synthesizer is a vintage chip that provides a unique and nostalgic speech output. In order to integrate this original speech chip into the Hero Jr robot, it was necessary to acquire the chip separately and design a compatible board.
Designing the Speech Synthesizer Board
The speech synthesizer board consists of several sections, including the microcontroller, speech circuitry, power supply, and RS232 interface. Let's take a closer look at each of these components.
4.1 The Microcontroller
The Atmega328 microcontroller was chosen for its versatility and familiarity. It offers sufficient I/O lines and is accompanied by a few necessary components, such as capacitors for bypassing and a programming connector.
4.2 The Speech Circuitry
The speech circuitry section includes inputs for phonemes and inflection levels. A transistor driver circuit is employed to accommodate the higher voltage requirements of the Votrax SC01A chip. Additionally, a strobe signal is utilized to trigger the chip for accepting new phonemes, and feedback is provided for error detection.
4.3 Power Supply
To power the speech synthesizer board, a boost converter is employed to convert the 5-volt power supply to the required 12 volts. This was necessary since the Votrax SC01A chip operates at a higher voltage than the rest of the robot's electronics.
4.4 RS232
An RS232 interface was incorporated into the design to allow communication between the Hero Jr robot and external devices, such as a computer. This feature enables the robot to speak through the RS232 port if desired.
Inputs and Outputs
The speech synthesizer board employs various inputs and outputs to facilitate communication with the Votrax SC01A chip and the external amplifier. Let's explore these connections in more Detail.
5.1 Phoneme Inputs
The microcontroller sends phonemes to the Votrax SC01A chip via six pins. These inputs are driven by logic-level signals and can be directly connected to the chip.
5.2 Inflection Inputs
The inflection inputs on the Votrax chip require higher voltage levels than logic signals. Therefore, transistor drivers are used to boost the voltage to the required level. Although it is technically out of spec, this configuration has proven to work effectively in other similar projects.
5.3 Strobe Signal
The strobe signal triggers the Votrax SC01A chip to accept a new phoneme. By controlling the timing of this signal, speech synthesis can be synchronized accurately.
5.4 Feedback
To ensure proper functioning and error detection, feedback from the Votrax chip is sent back to the microcontroller through a resistor for protection against potential issues.
5.5 Audio Signal
The audio output from the Votrax chip undergoes some conditioning, such as passing through a capacitor-resistor network before reaching the preamp volume control. This control allows adjusting the volume of the synthesized speech.
5.6 CB Line
The CB line on the Votrax chip is responsible for driving the audio amplifier directly. However, in this setup, a separate amplifier (TPA2016) is utilized instead.
Choosing an Amplifier Board
To further enhance the audio output quality, an amplifier board was selected. The TP2016 amplifier board from Adafruit was chosen due to its I2C control feature, which allows software volume control and greater flexibility in adjusting the audio parameters.
Voltage Issues
It was discovered that the Votrax SC01A speech synthesizer chip requires a higher voltage (around 9-12 volts) compared to the 5-volt power supply initially planned for the Hero Jr robot. To address this issue, a boost converter was added to provide the necessary voltage. Fuses and TVS diodes were also incorporated for protection.
Troubleshooting and Bug Fixes
During the initial stages, some issues were encountered, such as excessive power consumption and heating of the Votrax speech chip. Through troubleshooting and bug fixing, three possible solutions were identified: changing the Type of capacitor used, adding a 10-ohm resistor on the power input, and fixing a software bug related to strobing.
Demonstration
Once the speech board was completed and tested, a demonstration was conducted to showcase its functionality. Using the handheld remote control, the Hero Jr robot was able to speak predefined phrases, sing nursery rhymes, and engage in interactive conversations.
Conclusion
In conclusion, the addition of the original Votrax SC01A speech synthesizer to the Hero Jr robot has brought back its authentic speech capabilities. With careful design and troubleshooting, the speech synthesizer board successfully integrates into the existing robot architecture, providing an enjoyable and nostalgic experience for both enthusiasts and newcomers alike