I have a new Mendalmax 1.5 with a Ramps 1.4/Mega 2650 and a RepRapDiscount Smart Controller LCD. I have the printer hooked up to a Windows 7 PC. With the power to the printer off and a USB cable plugged into the Mega 2650 board the LCD turns on. If I unplug the USB the LCD turns off. If I plug the ribbon cable connected to EXP1 the LCD turns off. Why is the LCD always on when the USB cable is plugged in? Shouldn't the LCD be off when the printer is not in use? Right now I am just unplugging the ribbon cable to EXP1 so that the LCD stays off when not in use. Can anyone tell me how to fix this. Thanks https://reprap.org/forum/read.php?4,442582,442582#msg-442582 Mon, 13 Apr 2026 05:00:43 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?4,442582,451185#msg-451185 https://reprap.org/forum/read.php?4,442582,451185#msg-451185
The Arduino is its own computer. It just happens that it gets its power from your Windows PC via the USB cable is all. When the arduino is powered up, it starts running its loaded program, in this case, the printer firmware which you downloaded to it. That printer firmware is what turns on the LCD screen, and starts it communicating with that. If you had an SD card with a print job on it, it could start that print job with zero intaraction with your Windows computer. It therefore could run the printer entirely without any connection to the Windows computer if you plugged the Arduino's USB cable into a phone or tablet charger. What you cannot do without the PC is to update the firmware, say if you need to change the steps per unit for one axis of your printer.

So it's not the Windows computer that is in control of the printer, it's the Arduino. It's the same as if you had a USB printer connected to a Windows machine on a network. You send your print job information to the Windows machine that has the printer, and it makes the printer produce a hardcopy. The printer is available as soon as the computer that it's connected to is on-line. The only difference is that in this case, it's the Arduino which is the computer in charge of the printer.

If you have a smart controller, then it should have an SD card slot. If that's the case, and you don't want any evidence that the printer is on when not in use, then I'd suggest that you use a USB power adapter on the printer's main switch, and use the SD card to transfer gcode from the computer to the PC, or just unplug the USB cable to the Arduino.

Personally, I prefer the screen being on, as it's a reminder that the Arduino is running as soon as it has power. Some computers keep the USB ports powered up even when the computer is off, particularly ones where the computer is in standby.]]> SupraGuy Reprappers Mon, 05 Jan 2015 11:32:34 -0500 https://reprap.org/forum/read.php?4,442582,449921#msg-449921 https://reprap.org/forum/read.php?4,442582,449921#msg-449921 Thanks, but my PC does not have USB 3.0 ports, it only has 2.0 ports. Its too old to have 3.0.]]> pdeyo Reprappers Fri, 02 Jan 2015 00:35:54 -0500 https://reprap.org/forum/read.php?4,442582,449910#msg-449910 https://reprap.org/forum/read.php?4,442582,449910#msg-449910 jrcaster Reprappers Thu, 01 Jan 2015 23:41:51 -0500 https://reprap.org/forum/read.php?4,442582,449888#msg-449888 https://reprap.org/forum/read.php?4,442582,449888#msg-449888 Windows 7 PC turned off - printer power is off and LCD is still lit --- Ramps 1.4 with Mega 2650 board
I also a Printrbot Plus with a LCD (Printrbot board with Printrbot LCD). If I plug this printer into the USB cable the LCD does not light unless the A/C power is turned on.

There must a setting in the firmware that can control this or is there a way to wire up a off/on switch.
I am still currently unplugging the EXP1 ribbon cable and I would rather not have to constantly plug and unplug the USB cable ( I do all my printing using this Windows 7 PC).

If anyone can give me some assistance I would appreciate it.]]> pdeyo Reprappers Thu, 01 Jan 2015 19:46:42 -0500 https://reprap.org/forum/read.php?4,442582,443293#msg-443293 https://reprap.org/forum/read.php?4,442582,443293#msg-443293 Ohmarinus Reprappers Sat, 13 Dec 2014 18:00:30 -0500 https://reprap.org/forum/read.php?4,442582,442978#msg-442978 https://reprap.org/forum/read.php?4,442582,442978#msg-442978 But if you have an issue like the backlight power only when plugged i usb and the ramps stop working whe disconecting usb or LCD really dimm, then you were using a mega clone(like most of us RepRapers) , you fried the ams1117 Voltage regulator on the arduino mega.
In this case, they are two solution,
1: supply 5v to your ramps and mega via the vcc pin on the raps and the 5v from the atx(you will have to cut/unsolder D1 prior powering the ramps externally)

2: Replace the ams1117 5v regulator. These are cheap on ebay, but the tricky parts here is actually to desolder the burned one without breaking anything.

Hope I helped so folks out here ;-)


Davachat]]> Davachat Reprappers Sat, 13 Dec 2014 02:20:50 -0500 https://reprap.org/forum/read.php?4,442582,442944#msg-442944 https://reprap.org/forum/read.php?4,442582,442944#msg-442944 A switch seems to difficult to hook up due to the design of the board.
If it can be controlled using G-code's I can't find what G-Codes to use.]]> pdeyo Reprappers Fri, 12 Dec 2014 20:10:42 -0500 https://reprap.org/forum/read.php?4,442582,442585#msg-442585 https://reprap.org/forum/read.php?4,442582,442585#msg-442585
The cct show its just powered threw a resitor (pins 15 and 16 of the lcd module)

It would be easy to add a switch into this just to break the power going to the backlight, more work and you could have it reprap controlled, but then you will still have to set you gcodes into the start and end file]]> Dust Reprappers Thu, 11 Dec 2014 23:18:20 -0500 https://reprap.org/forum/read.php?4,442582,442582#msg-442582 https://reprap.org/forum/read.php?4,442582,442582#msg-442582 Why is the LCD always on when the USB cable is plugged in? Shouldn't the LCD be off when the printer is not in use?
Right now I am just unplugging the ribbon cable to EXP1 so that the LCD stays off when not in use.
Can anyone tell me how to fix this.

Thanks]]> pdeyo Reprappers Thu, 11 Dec 2014 22:52:11 -0500