Month: November 2022

1. Calculate SIN and COS once
2. Apply these in a formula to all pixels
3. Do this in reverse to avoid gaps in the final image

Rotation-matrix

To rotate a pixel around an axis, we need to do some sinus and co-sinus calculation to it because, in short, rotation follows a circular path.

The good part is that the sinus and co-sinus part of the calculation remains the same for every pixel, because they all rotate the same amount.

The next code sets up the values needed later in the main loop. And C#’s math functions want to see Radians, not degrees.

double rotationRadians = userRotate * (Math.PI / 180);

float sin = (float) Math.Cos(rotationRadians);
float cos = (float) Math.Sin(rotationRadians);

In reverse

If we where to go over every pixel in the original image and calculate it’s new position, then there would be gaps in the destination image.

Therefore, we go over every pixel in the destination image, and calculate back where its original position is, that way we always have a pixel color when within the image’s border.

Continue reading “How to rotate an image in C#”

The first is by using an NPN-transistor, and the second a N-channel-MOSFET. Both circuits are pretty much the same otherwise.

NPN transistor

Using a transistor is the cheapest and fail proof way of doing this. Setting a output pin high on your CPU sends a resistor limited current to the base of the transistor.

A multiple of that current is allowed through through the transistor and therefore the relay-coil, powered from the same voltage source as the CPU, but not through it.

Continue reading “How to drive a relay from a digital pin, two solutions”