Teensy Prop Shield – LC – Low Cost (no Motion Sensors) Generic / OEM

DESCRIPTION

This low-cost Prop Shield is meant for making light and sound effects on small handheld props and wearable costumes.

• Audio Amplifier– Clear quality audio output to a small speaker.
• Fast LED Driver– Drive APA102 / Dotstar LEDs for colourful lighting with rapid response.
• Flash Memory– 8Mbyte storage for images, sound clips, and data logging.

This shield features a 2-watt audio amp, high speed 5V buffers for driving APA102 LEDs, and an 8 Mbyte flash memory for images, sound clips, or data logging. It’s approximately the size of a Teensy, just slightly longer to allow space for mounting holes and connections for power, speaker, and LEDs

FEATURES

Audio Amplifier

The Prop Shield has a 2-watt audio amplifier, capable of driving 4 or 8-ohm speakers. 4-ohm car speakers work very well for permanent installations where louder sound levels are needed.

By default, the amplifier remains in a low power mode. You must drive pin 5 high to turn on the amplifier. It typically needs 8 milliseconds to wake up.

void setup() {
  pinMode(5, OUTPUT);
  digitalWrite(5, HIGH); // turn on the amplifier
  delay(10);             // allow time to wake up

With Teensy 3.2, the Teensy Audio Library can be used to create sounds. Nearly all the audio library examples are designed for the Audio Shield. To adapt them for the Prop Shield, replace “i2s1” with “dac1” in the Design Tool, or AudioOutputI2S with AudioOutputAnalog in the Arduino code. Then delete the SGTL5000 object and any code which uses it.

By default, the audio library will create a 1.2Vp-p signal at the DAC pin, which is a comfortable volume level for listening in a quiet room, but not nearly the amplifier’s full power. To get louder output, set the dac1 object to use EXTERNAL reference. Doing this before powering up the amp will avoid a loud click.

  AudioMemory(20);
  dac1.analogReference(EXTERNAL); // much louder!
  delay(50);             // time for DAC voltage stable
  pinMode(5, OUTPUT);
  digitalWrite(5, HIGH); // turn on the amplifier
  delay(10);             // allow time to wake up
  

For fine volume control, use a mixer object just before the DAC output in your audio design, where your code can control the mixer gain to change the volume.

On Teensy LC, the Talkie library can be used for simple voice synthesis.

Fast LED Driver

The Prop Shield has 5V buffers meant to send data to Dotstar or APA102 type addressable LEDs.

Normally the FastLED library is used to control these types of LEDs. The Prop Shield uses pin 7 to control access to the LEDs. If no other SPI chips are used, it can simply be set high in setup().

#include <FastLED.h>

#define NUM_LEDS 144
CRGB leds[NUM_LEDS];

void setup() {
  delay(2000);      // sanity check delay
  FastLED.addLeds<APA102, BGR>(leds, NUM_LEDS);
  pinMode(7, OUTPUT);
  digitalWrite(7, HIGH);  // enable access to LEDs
}

void loop() {
  // Move a single white led 
  for(int n = 0; n < NUM_LEDS; n++) {
    leds[n] = CRGB::White;
    FastLED.show();
    delay(8);
    leds[n] = CRGB::Black;
  }
}

When other SPI communication is used, pin 7 must be HIGH to allow LED access and LOW to prevent other SPI chips from interfering with the LEDs. The SPI transactions functions should also be used. You will need to include SPI.h to have access to these SPI functions.

    // beginTransaction prevents SPI bus conflicts
    SPI.beginTransaction(SPISettings(24000000, MSBFIRST, SPI_MODE0));
    digitalWrite(7, HIGH);  // enable access to LEDs
    FastLED.show();
    digitalWrite(7, LOW);
    SPI.endTransaction();   // allow other libs to use SPI again

Flash Memory

The Prop Shield has an 8 Mbyte flash memory, meant to storing 
sound clips, images, logging data, or other uses.

The SerialFlash library is used to access this memory.

Use TeensyTransfer to copy files to the flash chip without an SD card.

RESOURCES

• LM48310- 2.6W Mono Class D Audio Power Amplifier
• W25Q64FV- 64 Mbit (8 Mbyte) Serial Flash Memory
• SN74AHCT1G08- Single 2-Input AND Gate