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14. Voice Prompt Car with Espeak and Pico2Wave

In this lesson, we’ll use two built-in text-to-speech (TTS) engines on Raspberry Pi — Espeak and Pico2Wave — to make the PiCar-X talk.

These two engines are both simple and run offline, but they sound quite different:

Espeak: very lightweight and fast, but the voice is robotic. You can adjust speed, pitch, and volume.
Pico2Wave: produces a smoother and more natural voice than Espeak, but has fewer options to configure.

You’ll hear the difference in voice quality and features, and then build a “voice prompt car” that announces its actions before moving.

Before You Start

Make sure you‘ve completed:

Install All the Modules (Important) — Install robot-hat, vilib, picar-x modules, then run the script i2samp.sh.

1. Testing Espeak

Espeak is a lightweight TTS engine included in Raspberry Pi OS. Its voice sounds robotic, but it is highly configurable: you can adjust volume, pitch, speed, and more.

Steps to try it out:

Create a new file with the command:

cd ~/picar-x/example
sudo nano test_tts_espeak.py

Then copy the example code into it. Press Ctrl+X, then Y, and finally Enter to save and exit.

from picarx.tts import Espeak

tts = Espeak()

# Optional voice tuning
# tts.set_amp(100)   # 0 to 200
# tts.set_speed(150) # 80 to 260
# tts.set_gap(5)     # 0 to 200
# tts.set_pitch(50)  # 0 to 99

# Quick hello (sanity check)
tts.say("Hello! I'm Espeak TTS.")

Run the program with:
```
sudo python3 test_tts_espeak.py
```
You should hear the PiCar-X say: “Hello! I’m Espeak TTS.”
Uncomment the voice tuning lines in the code to experiment with how amp, speed, gap, and pitch affect the sound.

2. Testing Pico2Wave

Pico2Wave produces a more natural, human-like voice than Espeak. It’s simpler to use but less flexible — you can only change the language, not the pitch or speed.

Steps to try it out:

Create a new file with the command:

cd ~/picar-x/example
sudo nano test_tts_pico2wave.py

Then copy the example code into it. Press Ctrl+X, then Y, and finally Enter to save and exit.

from picarx.tts import Pico2Wave

tts = Pico2Wave()

tts.set_lang('en-US')  # en-US, en-GB, de-DE, es-ES, fr-FR, it-IT

# Quick hello (sanity check)
tts.say("Hello! I'm Pico2Wave TTS.")

Run the program with:
```
sudo python3 test_tts_pico2wave.py
```
You should hear the PiCar-X say: “Hello! I’m Pico2Wave TTS.”
Try switching the language (for example, es-ES for Spanish) and listen to the difference.

3. Voice Prompt Car

Now let’s combine Pico2Wave or Espeak with PiCar-X driving code to create a “voice prompt car”: before every action, the car will announce what it’s about to do.

Run the Code

cd ~/picar-x/example
sudo python3 14.voice_promt_car.py

Run this code and you’ll see your PiCar-X drive forward, backward, and turn, each time announcing its move first. This makes your car safer, friendlier, and more interactive.

Code

from picarx import Picarx
from picarx.tts import Espeak
import time

# If you want to try Pico2Wave instead of Espeak, uncomment below:
# from picarx.tts import Pico2Wave
# tts = Pico2Wave()
# tts.set_lang('en-US')  # Options: en-US, en-GB, de-DE, es-ES, fr-FR, it-IT

px = Picarx()
tts = Espeak()

# Quick hello (test)
tts.say("Hello! I'm PiCar-X.")

def main():
    try:
        # Forward
        tts.say("Moving forward")
        px.forward(30)
        time.sleep(2)
        px.stop()

        # Backward
        tts.say("Moving backward")
        px.backward(30)
        time.sleep(2)
        px.stop()

        # Turn left
        tts.say("Turning left")
        px.set_dir_servo_angle(-20)
        px.forward(30)
        time.sleep(2)
        px.stop()
        px.set_dir_servo_angle(0)

        # Turn right
        tts.say("Turning right")
        px.set_dir_servo_angle(20)
        px.forward(30)
        time.sleep(2)
        px.stop()
        px.set_dir_servo_angle(0)

    except KeyboardInterrupt:
        # Stop if interrupted
        px.stop()
    finally:
        # Reset to safe state
        px.stop()
        px.set_dir_servo_angle(0)

if __name__ == "__main__":
    main()

Troubleshooting

No sound when running Espeak or Pico2Wave
- Check that your speakers/headphones are connected and volume is not muted.
- Run a quick test in terminal:
```
espeak "Hello world"
pico2wave -w test.wav "Hello world" && aplay test.wav
```
If you hear nothing, the issue is with audio output, not your Python code.
Espeak voice sounds too fast or too robotic
- Try adjusting the parameters in your code:
```
tts.set_speed(120)   # slower
tts.set_pitch(60)    # different pitch
```
Permission denied when running code
- Try running with sudo:
```
sudo python3 test_tts_espeak.py
```

Comparison: Espeak vs Pico2Wave

Feature	Espeak	Pico2Wave
Voice quality	Robotic, synthetic	More natural, human-like
Languages	Default English	Fewer, but common ones
Adjustable	Yes (speed, pitch, etc.)	No (only language)
Performance	Very fast, lightweight	Slightly slower, heavier