Enclosure controller

As mentioned in an earlier post I have a plan to add an Arduino Uno based controller for enclosure. Its responsibility is to monitor temperature, control ventilation fan speed and switch on the main relay. It also has a simple 1602 LCD display shield for temperature and other information. At the moment I haven't planned any use for the keys of the display shield.

So far I have been testing the design on a breadboard in order to get temperature reading and relay control working. I have plenty of 100k Ohm NTC 3950 thermistors so I used one to measure temperature using voltage divider circuit and Steinhart–Hart equation in the Arduino code. There are plenty of examples online how to wire this up.

The main relay is an automotive 40A relay with integrated fuse socket. The funny thing was it actually came with a 30A fuse. That should be enough, though. In order to energise the coil of the relay I used BC548 NPN transistor. I also added 1N4148 as a flyback diode.

Adding a PWM controlled 12V should be straightforward. I will use BC548 or BC639 but I might add a capacitor to smooth out the fan control. After I have that sorted out on the breadboard I'll solder everything together.

Polarity matters

I was reorganising the cabling after I installed the cooling fans next to the hot end. I checked there were no loose ends and everything seemed to be fine. But as soon as I turned the PSU on there was a faint popping sound and no lights on the LCD. I managed to connect wires from PSU to RAMPS wrong way and that instantly fried RAMPS.

Looks like the LCD and MEGA are okay though, I was able to turn them on with USB power and use different features on the controller. However, none of the steppers move and the hot end wont warm up. Just to make sure I decided to order new RAMPS, MEGA and stepper drivers again. This will mean couple weeks pause with printing but I'll use that to design and build an enclosure for the printer.

Enclosure planning

While waiting some parts to arrive I have been thinking what kind of enclosure this printer will get. There are several reasons to have one and most of them are related to safety. I am planning to have HEPA and carbon filter for the exhaust in order keep the fumes and particles in minimum. The enclosure also serves as a sound proofing and depending on material and design some fire protection might be achieved. Naturally the temperature can be controlled better inside enclosure and this should improve print quality on ABS and some other materials.

I happen to have a spare Arduino Uno which will became the controller of the printer main relay. The actual printer hardware like RAMPS, Steppers and heated bed are powered by 12V line through that relay. Arduino Uno will monitor temperature readings and keep the relay closed only if values are within safe limits. It will also control enclosure exhaust fan speed in order to maintain desired enclosure temperature.

The design and materials of the enclosure are still undecided. Most likely something like a 50 x 50 x 50 cm cube with door on one side.