3D Printer Heated Bed Circuit Review

Design Reviews
#1

Hey guys,

I’ve always been in love with electronics, but just now I’m starting to prototype something other than blinking LEDs on breadboards. Right now I’m trying to build my own 3D printer. I started out with the heated bed circuit and at this point I wanted some feedback from someone more with more experience to know if I’m in the right direction.

I am eager to absolve any knowledge that the community might throw on this topic. The circuit I have so far consists of an N-Channel MOSFET switching power to a heater (the 3D printer heated bed) and reading the temperature through a thermistor. The temp control algorithm will be on the ATMega168A as well as the LCD information rendering. If anyone is interested and wants to contribute, I’m open.

Here is what I have so far:

3D Printer Heated Bed by brunobasto 0fc6780d220ee049 - Upverter

Thanks,

#2

Couple of quick notes:
Shoot-thru could be a problem on the totem arrangement of the two H11A817 outputs. When the D10 switches, both could conduct for a moment and there is nothing to limit the current flowing from 12V to gnd.
Also on the H11A817, it doesn’t appear to be available anywhere. Check distributors before designing parts in, it’ll save you frustration at assembly time.
Quick look at the mega, notes: “. If the ADC is used, it should be connected to VCC through a low-pass filter” when referring to AVCC. Probably just an RC filter will do the job.
You going to do programming off board and have a socket for the mega?

#3

Hello @lieser!

Thank you very much for replying to my thread. I was starting to believe this Forum was dead LOL

  1. I imagine that to solve the shoot-thru issue a resistor would be enough?

  2. For the H11A817, I actually have a few laying around here and here in Brazil some websites have it in stock.

  3. Thanks for the tip on the ADC issue. I’ll try adding a low-pass filter.

  4. I’ll add an ICSP header to program it. Since I’m a beginner, I didn’t want to complicate routing that much. But It’s definitely something that crossed my mind while designing it.

I don’t want to take much of your time, but, do you have any tips on components placing on the board to facilitate routing? Keep in mind that I choose thru-hole components to facilitate assembly.

Cheers,

#4

And yes, I’ll actually place a socket instead of solder the mega directly to the board.

#5

Yup, series resistor will be fine to limit shoot-thru.
Start by placing the critical items, like the processor and the crystal (they should be close together.) Then your high current paths like the fet and the power/heater connectors. Then just keep moving things about watching the rats-nest and try to make it as simple as possible. Note where you can change the pins on the processor to make the routing easier. As many of hte processor pins can be set in firmware to do various jobs.

#6

Awesome! Thank you!

Working on assembly on a perfboard for now just to make sure I have something working. Will post pictures here for reference cause it may be helpful for other beginners.