Really the only part of my Prusa i3 MK2 clone build that didn’t function as it should out of the box was the LCD Module with builtin SD card reader, rotary encoder, buzzer and stop button.
In this video I discuss how I tracked down the issues and fixed them. I also changed the ribbon cables for shielded cables as I needed them for how I was mounting the module – but it also assisted with preventing corruption.
The model I have is pictured below and its full title is a Bigtreetech RepRapDiscount Full Graphic Smart Controller.
Bigtreetech LCD Module, RepRapDiscount Full Graphic Smart Controller
During my trawling of the internet trying to find specific data for this LCD, (which I didn’t..) I used information from the documents below to build my own schematics, which are at the bottom of this post.
For anyone wishing to tear apart an HDMI cable to use as a shielded cable to the LCD Module, here is a pin diagram for a standard HDMI cable. (Although that isn’t much use as we are only using it as a general shielded multi-core cable! A decent HDMI cable has 7 single cores, and 4 twisted pairs inside their own separate shielding. This gives us 15 conductors, ignoring the shielding. The one I chose also had a metal braided wrap around the whole thing – I earthed them all to building earth)
Continuing with my mission this week to actually finish the electrics on my DIY Prusa i3 MK2 3D Printer, in this video I make some modifications to the RAMPS board and the Arduino.
On the RAMPS I need to remove the 4 pin power connector. Now that the RAMPS board is not carrying the current to the heated bed it isn’t really a safety issue (although it might be if yours is carrying heated bed power…) but it just simply takes up too much space for how I want to mount it. And a soldered connection is more reliable that a connector, well usually!
I am also junking the polyfuses. Again not so much a safety issue now as there is only a little current going through them, but even so the 5 Amp one still feeds everything apart from the heated bed so they have to go. Replacing them with a simple blade fuse holder and fuses – you know, like off of cars n stuff 🙂
In the last video I created a separate MOSFET board to handle power to the heated bed. The gate of the MOSFET is driven high by pin D8 of the Arduino, so I also add a signal wire from D8 that can then attach to my off-board MOSFET.
Lastly, I remove the DC jack on the Arduino. It isn’t being used or causing any issues, but I just don’t like it… well no, it got in the way of my board mounts.
That just leaves fixing the corrupted garbage that appears on the LCD after a couple of minutes. After quite a lot of time spent (more than quite a lot..), I have fixed it. That will be the subject of my next video.
I have changed my mind a few times about how I plan to finish off my Prusa i3 MK2 clone 3D printer… but now I have settled on a plan! None of it was particularly complicated, but I just want to arrange things in such a way that they are safe, tidy and give me the best result.
As I plan to add a physical brace to the Z Axis frame, I want to combine that with a suitable housing for all the electronics. With the actual brace made I can start finishing off the electronics!!!
There are few items I want to do:-
Fix the issues with LCD corruption – presumably cause by electrical noise
Remove the Polyfuses and provide alternative
Integrate the Raspberry Pi in with the other electronics so it is a permanent feature on the printer, including power
Add in additional temp sensors to the electronics and power supplies that will kill the power if anything looks dodgy
Power the Heated Bed with 24V instead of 12V – but keep this 24V separate from the RAMPS board
The last of these is the item I am doing first – and it the subject of this video.
Below is my rough schematic showing how I will wire the RAMPS, Arduino and also a small external board that will perform the heated bed power switching. Beneath that the calculations I made to conclude that the AUIRFB8409 Mosfet would work fine:
Rough Schematic of an external board to switch power to the 24V heated bed, showing relevant parts of the RAMPS and Arduino
Main considerations in choosing the AUIRFB8049 Mosfet, with calculations
As I am not sure yet exactly where the RAMPS will end up, I am just going to wire everything long and hook it all up temporarily to get the printer up and running. I will revisit the wiring once everything is working and tidy it all up. But this is good enough for now!
I cover a few little things that I needed to look up, pin outs etc. The rest was an easy job… so long as you have the right crimps to hand!!!
If you have a Z probe that needs more than 5v to operate, then you can run it directly from the 12v supply and run the signal wire (usually black) through a voltage divider and from there into the RAMP Z Min Endstop connector.
The values for the voltage divider are R1=10kOhm and R2= 6.8kOhm. This will drop the 12v to 4.9 and result in a power loss of only 85mW.
I didn’t end up needing to do this – although the probe was spec’d for 6-36 Volts (if I remember correctly) it worked fine with just 5v.