CatDetect - a touchless and remote door bell

The Story behind this project

My parents have three cats and they are allowed to roam outside in the backyard and the gardens in the neighbourhood during the day. But in the evening when it dawns we like to have them inside where it's warm and safe. Especially in winter it's important that they're in before it gets too cold. However, one cannot watch the door the whole day and look whether they want in or not; and a cat flap would allow them to bring all kinds of mice and other pests inside. That's the story how it came to this little project.

A chart recorder printing text

Chart recorders were pretty neat devices to graph time curves of analog values, such as temperature changes. My dad had still a pair of MFE 4144 thermal line recorders in his cabinet of replacement parts. However, the device using those modules is discontinued for now about two decades and he asked me whether I could make use of them.
Luckily, my dad found the schematics and the pin mapping of the recorder, so attaching it to a microcontroller was pretty easy. The supply voltage is 12 V; I power it from a bench power supply. It takes 5 parallel TTL signals as a forward speed selection (a microcontroller drives a stepper motor), and a +/-2 V analog signal for the 'pen' position. The 'pen' is actually a needle that is being heated by a resistor. The thermopaper stains in a nice blue color when having contact to that hot metal.

Hello World

Hi folks,

I'm Marvin - Marv for short - and I'm an 18 year old student of electrical engineering and computer science (2014). I created this blog in order to share my work and ideas with the world. I won't get to specific on what I'm going to post, it can be anything from artistic work, music and videos to programming, electronics and hardware hacking - and maybe even something completely different. I just don't know yet. ;)

Enjoy :)

- Marv