RDK S100 40-pin GPIO and PWM¶

This handbook follows the recorded course slides, including wiring, commands, measured results, and the scope of verification.

Source slides

Verify digital output and hardware dimming with one LED.

Two visible hardware checks¶

The same LED verifies switching first and continuous brightness control next.

GPIO output¶

Pin 37 alternates HIGH and LOW so the LED blinks.

PWM dimming¶

Pin 33 outputs 48 kHz PWM with a changing duty cycle.

Evidence¶

Wiring photos, camera footage, and sample output support the result.

40-pin wiring limits¶

S100 digital I/O uses 3.3 V logic. This lesson only uses signal and ground from J24.

Wire the circuit with power off
Always place a 330 ohm resistor in series with the LED
Never short a GPIO output to 3.3 V or ground
Use BOARD physical pin numbering
Call GPIO.cleanup() when the program exits

Digital output has two states¶

HIGH¶

The output approaches 3.3 V and current flows through the LED.

LOW¶

The output approaches 0 V and the LED turns off.

Periodic toggle¶

The sample changes state once per second.

Clean exit¶

Ctrl+C stops the loop and releases the pin.

GPIO wiring on the board¶

Connect J24 Pin 37 to 330 ohms, then the LED anode. Return the cathode to Pin 20 ground.

RDK S100 GPIO LED wiring

Pin 37 → 330 Ω → LED → Pin 20 GND

Run the official output sample¶

The board sample uses BOARD numbering and toggles the output continuously.

Command¶

sudo python3 /app/40pin_samples/simple_out.py

Press Ctrl+C to stop.

Core logic¶

GPIO.setmode(GPIO.BOARD)
GPIO.setup(37, GPIO.OUT)
GPIO.output(37, HIGH / LOW)

The state changes once per second.

GPIO verification flow¶

Power offCheck Pin 37 and ground

Power onWait for a stable system

RunStart simple_out.py

ObserveLED blinks regularly

ExitCtrl+C and cleanup

Duty cycle controls brightness¶

Frequency¶

The sample stays at 48 kHz, far above visible flicker.

Duty cycle¶

A larger HIGH-time ratio increases average LED brightness.

Hardware channel¶

S100 40-pin Pins 32 and 33 support LPWM.

Visible result¶

Brightness rises from 25 percent to 100 percent, then falls.

PWM wiring on the board¶

Keep the resistor, LED, and ground. Move only the signal wire from Pin 37 to hardware PWM Pin 33.

RDK S100 PWM LED wiring

Pin 33 → 330 Ω → LED → Pin 20 GND

Run the hardware PWM sample¶

simple_pwm.py uses 48 kHz and changes the duty cycle in five-percent steps.

Command¶

sudo python3 /app/40pin_samples/simple_pwm.py

Pin 33 must not be used by another function.

Parameters¶

GPIO.PWM(33, 48000)
ChangeDutyCycle(25 ... 100)

Five percent every 0.25 seconds.

PWM verification flow¶

Power offMove signal to Pin 33

Power onKeep resistor and ground

RunStart simple_pwm.py

ObserveLED fades up and down

ExitStop PWM and cleanup

Two outputs, different jobs¶

GPIO¶

Best for on/off control with only HIGH and LOW.

PWM¶

Best for average-power control such as dimming or speed.

Shared acceptance¶

Correct wiring, visible behavior, and resource cleanup.

Checks when nothing happens¶

Inspect the physical circuit before permissions and pin ownership.

Step 1

Power off and check LED polarity, resistor, and ground.

Step 2

Confirm BOARD Pin 37 or Pin 33 in the program.

Step 3

Run with sudo and stop any process using the pin.

Step 4

Restart the test without moving wires while powered.

complete¶

One LED has verified both GPIO blinking and PWM dimming on the S100 40-pin header.

Repeatable wiring¶

Pins 37 and 33 serve the two experiments.

Visible behavior¶

Camera footage preserves blinking and fading.

Next lesson¶

Continue with UART and I-squared-C communication.