My version of the Printrboard LCD Controller

Well, I designed the board, routed it, checked it, and sent it out to be fabbed…

Got my boards in and built one only to realize, I had made an error :(. I got my 5V and GND connections reversed. I don’t know how I did this, but I did. So here I sit with 10 boards with reversed power connections.

Being the person I am, I’m not going to let that stand in my way of seeing if the design works otherwise so Here is my build progress.

The blank board looks like this:

PCB TOP Side (Encoder, display, and Reset button mount on this side)

PCB Bottom (14 Pin Connector, Switch, .1uf Capacitor, Backlight Resistor, and Contrast Pot mount on this side)

And the close up of the connector showing pin 2 going to ground with Pin1 being VCC…. ARRGH


Well, I built the board anyway. For a temporary fix, I used a 10 pin connector on pins 5 thru 14 and a two pin connector for the power and ground (Pins 1 & 2) so I could reverse them. Once assembled, the board looks like this:



By now, you may be wondering what the reset button and switch are for. Well, it so happens that the Printrboard does not use three pins of the 14 in the connector. So, I designed this board to use those pins if a custom cable is used. On my board, pins 3 & 4 which are normally not connected, can be broken out to the two boot pins on the printrboard. Pin 9 which is normally not connected, can be broken out to the reset pin found in the 6 pin header on the printrboard. By doing this, you can reset the printrboard by pressing the reset button. Firmware can be uploaded by turning on the switch then pressing the reset button to enable firmware mode. Normal run mode is with the boot switch off. I haven’t yet tested these options, but they should work.

I’ve corrected the schematic and board files for my board, and will make them available shortly. They are licensed under Creative Commons Attribution-ShareAlike 4.0 International License.


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9 Responses to My version of the Printrboard LCD Controller

  1. Nick says:

    Were any software/firmware changes necessary to make this function?

  2. Bill Brown says:

    Rick, what would you charge to build a complete lcd for my PB simple metal with heated bed? I do not have the technical know how to soldier all the connectors. I can plug and play that’s about it.

    • Rick_S says:

      I’m sorry, I don’t do that. I have other full time commitments that take most of my time. That’s why the blog doesn’t get updated as much as I’d like to. If you don’t have the ability to build yourself, you might look at the official printrbot LCD boards, go the RepRap Smart controller with a custom cable like I described in this post ( ), or see if there is a builder community local to you who could help you out.

      The hardest part about going the RepRap Smart Controller route, is making the cable. However, most people can do this with an inexpensive crimping tool found on Amazon, and some crimp pins and housings (I purchase these from Pololu ). I sacrificed an old VGA cable when I made mine.


  3. Hunter Halcomb says:

    Hey Rick, I was wondering if you could help me figure out what resistor I need for R1 on my board. I’m using a J204A LCD. It looks like it has a resistor onboard for pin 15 of 68 ohms. How do I go about calculating what to use?

    • Rick_S says:

      It really depends on the way the board is setup. The datasheet for your LCD should help you with that, but if it doesn’t, every LCD I have, worked fine with a resistor of 100 to 560 ohms 1/4W. Depending on the LED backlights, I think the lowest value I’ve used was 39 Ohm. If you are unsure, test it with a higher value with jumpers prior to the final build. I’m currently using a 100 Ohm resistor in my display and the backlight is plenty bright. It’s also quite possible that the 68 Ohm resistor you see on the board is the current limiting resistor and no other is required for 5V operation. If that is the case, R1 can be replaced with a jumper. However, I normally like the backlight a little less than full bright anyway so adding another resistor inline doesn’t hurt and can be easier on the eyes :D.

      Let me know how the build goes!


  4. Rick_S says:

    Most recently, I compiled my own based on one of the branches of the Printrbot variation of the Marlin firmware found here. The reason I compiled my own was to be able to change the VID/PID numbers so the computer (Windows 8.1) would see the printer as a 3d printer and not just a serial device. Otherwise, if you just wanted to update the HEX file, the one linked at was what I was using. I would have to double check, but I don’t think either of these firmwares are setup for I2C though. If not, you would have to turn that on and re-compile anyway. Even then, I don’t know if it’d support my I2C board w/o modifying the I2C routines in the firmware since I didn’t use the I2C chip commonly used by several LCD adapters.

  5. Ralph Hulslander says:

    Well Rick you know I want one. I have been thinking of integrating your I2C led project with my Printrboard for my Two Up. What firmware do you use?

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