TTL Signal deformation

package ttldeformation;
import sk.uniba.fmph.pocprak.simplegraphics.*;

public class TTLDeformation {
    static GrGraphics gr = SimpleGraphics.CreateGrEnvironment();

    public static void main(String[] args) {
        double time = 0;
        double dt = 0.001;
        double period = 1;
        double outputVoltage = 0;
        double dU = 0;
        double RC = 0.1;
        prepareGraph();
        for(; time<3; time=time+dt){
            dU=(1/RC)*(inputVoltage(time, period)-outputVoltage)*dt;
            outputVoltage = outputVoltage + dU;
            paintGraph(time, outputVoltage, dU, dt);
            //System.out.println("time elapsed: "+time+" Voltage Shift: "+dU+" output Voltage: "+outputVoltage);
        }
    }

    /**
     * Generates TTL over time
     * @param t - time elapsed
     * @return int value of voltage
     */
    static int inputVoltage(double t, double period){
        if(Math.sin(t*(2*Math.PI/period))>0)
            return 5;
        return 0;
    }

    /**
     *
     * @param t - time elapsed
     * @param voltage
     */
    static void paintGraph(double t, double voltage, double dU, double dt){
        gr.drawLine2D(t, voltage-dU, t+dt, voltage);
        gr.repaint();
    }

    /**
     * draws axis & scale & stuff
     */
    static void prepareGraph(){
        gr.margin=50;
        gr.setBasePoint(gr.LL);
        gr.setUserFrameSize(0.,0.,3.5,5.5);
        GrAxisX xaxis = new GrAxisX(0.,3.5,0.);
        xaxis.setLTicks(0.0,0.5);
        xaxis.draw(gr);
        GrAxisY yaxis = new GrAxisY(0.,5.5,0.);
        yaxis.setLTicks(0.0,0.5);
        yaxis.draw(gr);
        gr.repaint();
    }
}