Lab 3: External digital inputs

Create a new application.

Zephyr’s logger module is not enabled by default. We need to request that it be included in the application by editing the prj.conf file. Add the following line to this file:

CONFIG_LOG=y

Add a build configuration and create a devicetree overlay. The contents should be the same as in the previous program (Program 2).

Enter the contents of Program 3 into main.c.

#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>
#include <zephyr/device.h>
#include <zephyr/logging/log.h> (1)

/* Get node identifiers using label */
#define RED_NI DT_NODELABEL(red_led)
#define GREEN_NI DT_NODELABEL(green_led)
#define SWITCH_NI DT_NODELABEL(slider)

/* Get gpio specs */
const struct gpio_dt_spec redLED = GPIO_DT_SPEC_GET(RED_NI, gpios);
const struct gpio_dt_spec greenLED = GPIO_DT_SPEC_GET(GREEN_NI, gpios);
const struct gpio_dt_spec slideSwitch = GPIO_DT_SPEC_GET(SWITCH_NI, gpios);

/* Register with logger */
LOG_MODULE_REGISTER(SlideCounter, LOG_LEVEL_DBG); (2)

int main() {
    bool currentSwitchValue, previousSwitchValue; (3)
    int n = 0; // slide counts

    LOG_INF("Slider counter program starting"); (4)

    if (device_is_ready(redLED.port)) {
        gpio_pin_configure_dt(&redLED, GPIO_OUTPUT_ACTIVE);
        gpio_pin_configure_dt(&greenLED, GPIO_OUTPUT_INACTIVE);
        gpio_pin_configure_dt(&slideSwitch, GPIO_INPUT);
    } else {
        LOG_ERR("GPIO port is not ready"); (5)
        return -1;
    }
    k_msleep(100);

    previousSwitchValue = gpio_pin_get_dt(&slideSwitch);
    while (true) {
        currentSwitchValue = gpio_pin_get_dt(&slideSwitch); (6)
        if (currentSwitchValue != previousSwitchValue) { (7)
            n++; (8)
            previousSwitchValue = currentSwitchValue;
            LOG_INF("Slide counts = %d", n); (9)
            gpio_pin_toggle_dt(&redLED);
            gpio_pin_toggle_dt(&greenLED);
        }
    }
}

Build the application and flash it to your development board.

In the nRF Connect side panel:

Press the reset button on your development board. It is the push button set off by itself. You should see something similar to the following in the terminal window in VS Code.

Figure 5. Start up logs from the slide counter application.

Now slide the switch to a new position. You might have expected a log message to appear, but it did not. This is because the logger is a low-priority task and only sends messages to the terminal when the main application lets it (for example, by sleeping);

Modify the code in main.c, adding k_msleep(1); as the first line inside the while loop.

Build the revised program and flash the board again.

Test the revised program, sliding the switch back and forth. Does it always behave as expected?

Connect the flywire labeled 1+ (top left, orange) to the same column as the output pin of the button (the one that is connected to P0.03). Connect the flywire labeled 1- (bottom left, orange with white stripe) to the ground bus strip. Connect the ground () flywire to the ground bus strip.

In the Time settings, change Position to 5 µs and Base to 2 µs/div.

In the Channel 1 settings, change Offset to -2 V and Range to 500 mV/div.

In the Trigger settings (above the graph), set Mode to Repeated and Normal and set Level to 2 V.

Click the Run acquisition button to repeatedly capture rising transitions without the need to restart.

Push the button, paying attention to the count and the WaveForms display. What do you observe?

Push and release the button until you observe the counter move forward to the expected count of 2. You will now save the corresponding oscilloscope capture to a Word document. Select File  Export and then select the Image tab. Under Comments, type “Button press, normal”. Uncheck Device, Serial Number, and Time. Then click on Copy to Clipboard.

Create a new Word document and paste your oscilloscope capture into it.

Now push and release the button until you observe the counter jumping forward by more than a count of 2. Export this oscilloscope capture with the comment “Button press, skip” and add it to your Word document.

In your Word document, write a brief description of the differences you observe in the two oscilloscope captures.