This is V.2 of a previous machine I had made out of balsa wood.
This one is 3d printed in ABS plastic and set on a base of beech wood.
A continuous rotation servo pulls a roll of receipt paper forward and small servo controls a pen.
The pen draws squiggly lines similar to an electrocardiograph or a sismograph.
A light sensor picks up the light from a candle and sends the information to an arduino which in turns controls the servos. When the light is strong, the pen draws to the left, when the light fades, the pen draws to the right.