Electronics

 

Since a cnc mill has no use for a heater or two (as far as i know) we need some extra electronics. We want to:

  • Set the Temperatures for the extruder and the heated bed in emc2
  • Measure the actual temperature
  • Control the power accordingly to out measurement

So we need a circuit which:

  • connects to our emc2 computer
  • has at least two ADCs (Analogue Digital Converter)
  • has at least two digital IOs (Power On/Off for extruder and bed
  • has two high current “switches” for the heaters

There are properly a zillon ways to achieve this. I decided to ride with pack and keep it simple:

An Arduino (or compatible) development board:

 

 

Two IRLZ 34N Mosfet Transistors, some Resistors, two LEDs and two capacitors combined to a custom build shield and two heatsinks (not shown):

If you want to build it as easy as possible, take perboard and omit everything but the two resistors for the voltage divider and the mosfets. Just be careful with the mosfet connections, the heated bed takes more than 10 Amps…

The attached eagle file is for a new version:

New board version

And of course a power supply. I choose a 12 DC switching power supply. It brings galvanic isolation from the mains which i really appreciate, it works with the reprap stuff (they use power supplies for Personal Computers)  and it will properly not even tickle if you try to electrocute yourself. Besides that it’s a poor choice, we need approx. 150 Watt so more than 10Amps. Next time i will go for 48Volt…

After quite some testing my thoughts about the heated bed changed. The PCB heated bed is alright for printing directly to it. It warps a little as it’s a PCB but you can do fine. If you attach it to a 5mm Aluminum Plate it would take ages to heat up and it will never reach 100 degrees Celsius. All heating mats I found on the interwebs are quite nice, waterproof, acid resistant and so on but also quite expensive.

The attached tar-file also contains the Sourcecode for the LinuxCNC integration.

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