LED bar chase

Drive several LEDs at once and run a "chase" — a lit dot that sweeps back and forth, like a Knight Rider scanner. It shows how to manage many GPIO lines from one program.

Wiring

Wire four LEDs, each through its own 330 Ω resistor to GND, on GPIO 17, 27, 22, 23:

GPIO17 ──▶│── 330Ω ── GND
GPIO27 ──▶│── 330Ω ── GND
GPIO22 ──▶│── 330Ω ── GND
GPIO23 ──▶│── 330Ω ── GND

(Use as many as you like — just extend the list in the code.)

Code

namespace Demo

import Amalgame.Hardware
import Amalgame.DateTime

public class Program {
    public static void Main(string[] args) {
        let pins: List<int> = [17, 27, 22, 23]

        // Request every pin as an output.
        for p in pins {
            if (!Gpio.PinMode(p, PinMode.Output)) {
                Console.WriteLine("could not open GPIO" + String_FromInt(p))
                return
            }
            Gpio.DigitalWrite(p, Level.Low)
        }

        // Light exactly one LED at a time, sweeping forward then back.
        var sweeps: int = 0
        while (sweeps < 6) {
            var i: int = 0
            while (i < pins.Count()) {
                Program.LightOnly(pins, i)
                DateTime.SleepMillis(120)
                i = i + 1
            }
            // back down (skip the ends so they don't double-blink)
            i = pins.Count() - 2
            while (i > 0) {
                Program.LightOnly(pins, i)
                DateTime.SleepMillis(120)
                i = i - 1
            }
            sweeps = sweeps + 1
        }

        Gpio.Close()
    }

    // Drive pin index `on` High, all the others Low.
    private static void LightOnly(pins: List<int>, on: int) {
        var i: int = 0
        while (i < pins.Count()) {
            if (i == on) {
                Gpio.DigitalWrite(pins.Get(i), Level.High)
            } else {
                Gpio.DigitalWrite(pins.Get(i), Level.Low)
            }
            i = i + 1
        }
    }
}

Run

amc package add datetime     # once — for DateTime.SleepMillis
amc build main.am -o ledbar
./ledbar

A single lit LED sweeps across the bar and back, six times.

What's happening

• The pins live in a List<int>, so adding LEDs is just editing the list — the loops don't change.
• LightOnly walks the list and drives one pin High, the rest Low. Replace it with your own pattern (fill, blink-all, binary counter…) for different effects.
• Everything is plain digital DigitalWrite. For smooth brightness (a fade rather than on/off), you'd reach for PWM — new Pwm(0, 0) in the same package — but that needs a PWM-capable pin and the dtoverlay=pwm overlay.

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