Serial to TD: One-way Communication Controlling an LED
Sections:
Introduction
When working with Arduino and TouchDesigner you may want TouchDesigner to control the behavior of an output. In this case we will start with changing the brightness of an LED.
We’ll build an LED circuit, and write code that tells Arduino:
- to use Serial Communication to receive one byte of information
- use that byte to control the brightness of our LED
We’ll create a TouchDesigner Network that tells TD to:
- to use a slider or a number generating CHOP to generate a value
- Use Serial Communication to send that value as one byte of information to Arduino
At the end our TD controller (slider or CHOP) should be controlling the brightness of our LED
This example uses the the free version of TouchDesigner 2023.11880 and the Arduino Nano 33 IoT. See Arduino Pinout here.
See more info here
Arduino Circuit
The circut uses the following components:
- Arduino Nano 33 IoT
- Solderless breadboard
- 220 Ohm resistor
- LED
- Hookup wire / jumper wire
To begin, set up the breadboard so that you connect the Arduino Digital Pin 2 to one end of a 220 ohm resistor. Connect the other end of the resistor to the Anode (the longer lead) of the LED. Connect the Cathode (the shorter lead) of the LED to GND. See reference image below.
Note: this example will use PWM. Make sure that the resistor-LED series is connected to digital pin 2 or any other PWM pin if you are modifying this example. PWM pins are labelled with a tilde symbol ~ in the Arduino Pinout Diagram.
Arduino Code:
Once the circuit is set up lets write code to receive data via serial communication and use that serial data to change the brightness of the LED.
First set up global variables for our LED’s brightness value and LED pin. The brightness value can be any number between 0 and 255 to start, the ledPin should be which ever pin you are connected to (Ddigital pin 2 in this example):
int brightness = 255;
int ledPin = 2;
Next inside of your setup() Use Serial.begin() to start communication at a baud rate of 9600. Remember the baud rate, it will be used later in your touchdesigner network.
Set your led pin (digital pin 2) as an output using pinMode()
void setup(){
Serial.begin(9600);
pinMode(ledPin, OUTPUT);
}
Inside of your loop() use the Serial.available() function to read incoming data. If there is data coming across the serial port the Serial.available() function will respond with the number of data bytes available. If Serial.available() returns a value greater than 0 that means we have received data from TD.
This also means whatever you put inside of this if statement will only execute if the Arduino has received information from Touchdesigner.
Inside our if statement (meaning once we have data) read that data and store it as an integer variable called incoming. Next assign the brightness variable to be the same value as the incoming variable.
Outside of the if statement, lets use analogWrite() to change the brightness of the LED. Since it is outside of the the if statement, it should default to maximum brightness (255) if we do not yet connect to TouchDesigner, and if communication is ever interrupted it will stay at its last received value
void loop() {
if (Serial.available() > 0) {
int incoming = Serial.read();
brightness = incoming;
// Serial.println(incoming);
}
analogWrite(ledPin, brightness);
}
Full Code below:
int brightness = 255;
int ledPin = 2;
void setup(){
Serial.begin(9600);
pinMode(ledPin, OUTPUT);
}
void loop() {
if (Serial.available() > 0) {
int incoming = Serial.read();
brightness = incoming;
// Serial.println(incoming);
}
analogWrite(ledPin, brightness);
}
The TouchDesigner Network:
Make the button control your port opening:
Use a button to open and close the Serial port. Create a button component (COMP), make sure the “Button Type” parameter is set to Toggle Up. Connect it to a null CHOP.
Next Create a serial DAT.
Make the null CHOP active and export it to the “Active” parameter of the serial DAT. Then make your button component active and click it to see if the serial DAT toggles on and off.
Serial DAT: Receive data
Click on the serial DAT. Set the parameters to read incoming information as such:
Row/Callback Format: “One Per Message”Port: Portnames should match what you see in your Arduino IDE (e.g. COM4, usbmodem14201, etc). Will differ by computer and usb portBaud Rate: 9600 (Baud should match your Arduino Baud)Data Bits: 8 (Default)Parity: None (Default)DTR: Enable (Default)RTS: Disable (Default)
Add a Control Slider
Add a slider COMP and connect it to a select CHOP
Make the slider active in order to interact with it, move the slider and look at the range of values it outputs
Also notice how the channel name is different from the other CHOP channesl. Our other CHOPs generate channels named chan1,chan2, etc, but the slider has generated a channed with the name v1.
To avoid any potential future conflicts you may want to rename the channel in the select tab of the select CHOP
Closer View: 
By default TouchDesigner uses normalized values (between -1.0 and 1.0) for nearly all operators. This means if we want to use the slider to control the brightness of the LED we need to map the slider’s initial range of 0-1 to 0-255 so that it can control the full range of brightness of the LED.
Connect the select CHOP to a math CHOP
Change the parameters of the math CHOP. First navigate to the OP Tab, and look for the Integer dropdown. Select Round
Navigate to the Range Tab and set the following fields:
From Range: minimum to 0, maximum to 1. This is the incoming range of the slider.
To Range: 0 255 minimum to 0, maximum to 255. This is the outgoing mapped value that we want to send to Arduino.
Make the slider active and observe how the range changes:
Lastly connect the math CHOP to a null CHOP.
If all is set up correctly you should be able to use the slider to output a value between 0 and 255.
Send a byte using a CHOP Execute script:
Create a CHOP Execute DAT.
The CHOP Execute DAT is designed to trigger specific functions whenever the target CHOP channel values have exhibited any of the parameter states or changes listed:
Off to OnWhile OnOn to OffWhile OffValue Change
For this case we will only use Value Change. We only want to communicate to Arduino when necessary, and for this interaction we only need to update our Arduino’s LED if there is a change in value.
Make sure the Value Change parameter is enabled.
Also make sure the CHOPs field refers back to the name of the null that your slider is connected to, otherwise it won’t know what component should be controlling the communication. In this example null2 is the CHOP connected to the button.
Make the chopExec DAT Active to enable editing directly in the DAT. We want to write a python script that will execute whenever the value changes. Make sure to only edit the onValueChange function
The onValueChange function has four parameters built in (and documented at the top of the script in the comments) one of them is the numeric value of the changed sample: val, this is our slider data.
When the value changes lets use the serial1 DAT to send the val to the arduino as a byte:
def onValueChange(channel, sampleIndex, val, prev):
op('serial1').sendBytes(val)
return
If all set up and connected correctly you should be able to activate the button use it to start communicating with the Arduino, then active the slider and use the slider to change the LED’s brightness.
At this point you can try connecting other operators in place of the slider. Try LFO or Noise and play with different options and mappings to automate how the LED brightness changes.