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General Purpose Outputs “GPO” are found on a lot of hardware. One of the more popular pieces of equipment to have them is Matrix Orbital’s line of LCD Displays. If you own, or plan to buy a Matrix Orbital LCD display, you’ve most likely been baffled by these little pins. It’s tempting to just go wild connecting wires every which place to try and figure these things out. Unfortunately that’s about the worst thing you could do. Many first time MO owners have damaged or even destroyed their displays by rushing in with both eyes shut. Today I’m going to walk you through a quick setup of the 12v GPO’s on an MX212. Hopefully this will be enough to get you safely started on your own crazy tangents of how to use this extremely versatile feature.

Fist a general overview.

The MX212 is equipped with a total of six GPO’s designed to control relays or other electronic devices. This allows external devices to be turned on or off using your PC or controller and software commands. There are two types of GPO’s, low and high power. GPO 1, 2 and 3 are referred to as Low Power GPO’s and are capable of sourcing +5V at 20mA which is limited with a 240 ohm current limiting resistors. GPO 4, 5 and 6 have no current limiting resistors and offer an optional +12V power through the white floppy connecter located bottom left of the display.

Let’s stop and take a look at what that paragraph is talking about. Notice that GPO 1 is actually the second row of pins from the top. Many people don’t realize this and end up going mad over why their GPO’s aren’t responding. I myself, fell victim to this phantom pin with my first display. The top line of pins is actually just an “always on” 5v power source. You can use this to provide power to additional LED’s if you wish, just don’t forget to add a current limiting resistor!

GPO’s can control 12V or 5V devices depending on the jumper selection. Maximum allowable current is 750 mA per GPO at 12V and 750mA a 5V which allows the GPO’s to be used for controlling fans, stepper motors, etc. without the need for a relay in many cases. When using the high power GPO’s with the +5V selection, note that the USB host can provide a maximum of 500mA on a high power host and 150mA on a low power host. The +12V line will be taken from your systems power supply so there should not be any need to be concerned with using more current then the power supply can supply.

Sweet! That means you can power just about anything 12v directly through your new MO! This is more than just a simple on/off switch. The GPO’s can be set to turn on/off/blink/strobe/flurb…ok, well maybe not flurb, but certainly all the rest at any interval or “trigger” you wish. So how do we turn these bad boys on? Simple, the last row of pins is the selector jumper; Depending on the position of the jumper, GPO’s 4 through 6 will either be 5v or 12v.

Ok, now for the quick walkthrough. The goal here is to have the 12v GPO activate a 12v strobe light whenever the CPU temperature reaches 45 degrees Celsius. Once the temperature drops back below 45, the strobe will stop.

First we’ll need some supplies. One Matrix Orbital 212, one 12v strobe light and a front bezel led wire from an old case. The strobes original purpose was for car audio uses, luckily though, most equipment made to run in a vehicle also works nicely in your case. As you can see, there are two wires leading off of the strobe; one black (negative) and one red (12v). Keep in mind that although your typical power supply will color code 12v in yellow, car audio equipment uses red.

These two wires will be connected directly to GPO 5 via an old led cable. Notice how I used the yellow to denote that this wire is carrying 12 volts. This avoids confusion later down. There’s nothing worse that splicing into a 12v cable that you thought was only carrying 5. In this picture you can also see I have 2 of the 5v GPO’s already hard at work on other tasks; again using red for 5v and yellow for 12v. Once you decide to use the 12v option on pins 4 through 6, you’ll need to attach a standard floppy power connector to the auxiliary power input provided. This allows you to use much more power than just your USB cable alone could handle. Every power supply should have at least two of these connectors so now’s your chance to put that second one to use or even the first one as most of us have ditched the floppy altogether.

Well that’s pretty much it on the wiring end. The GPO should be shorted by default, so the strobe won’t be doing its thing until we tell it how. Notice how I said “shorted”; I say that to emphasize the point that there IS 12 volts now running through that yellow wire. Even though the GPO is not activated, it still carries power. Take the time to finish up all your wiring before you plug the tail into the GPO. Failing to do this could cause a short, damaging your display and possible much more.

Now to get it all to work the way we planned. Using LCDC that was packaged with the MX212, we create the actions we want in the ScreenBuilder. As you can see I have it set to monitor the Motherboard Monitor 5 reported Athlon temperatures and turn on GPO 5 when it reaches a temperature greater than or equal to 45 degrees Celsius. The beauty of LCDC is that you don’t even need to have a strobe light in order to create this effect. If you use any other 12v “non-strobe” light source, you can set the action to Gpo- > Strobe, instead.

Of course this will quickly drive you mad, so we need a way to stop it. Again, LCDC makes things simple for us. Simply create another action to monitor when the temperature falls back below 45. This time, we have it turn the GPO off.

That’s it! Nothing to it! Now you should no longer be intimidated by those little pins. This method can be used in an endless number of situations. Other accessories that can be controlled via the 12v outputs include cold cathodes, video screens, and fans. Here is the final outcome. It’s quite a sight to look at. Now, whenever I see the strobe a callin’, I can simply reach over and turn up the fan speeds. Good luck on your future projects and make sure to check out GruntvillE’s DawG PounD Member’s Forum for tons of helpful information on LCDs, MoDs, HardwarE and OverclockinG!

If you liked this How-To but still crave more info on LCD Displays; make sure to check out these great reviews including the HOT new USB MX212 used in this GrunT GuidE. Of course you could also swing by Matrix Orbital to get information on all their LCDs. If you find one you like that we haven’t yet reviewed; swing by our Review Request Area and let us know about it. You’ll need to register in the forums if you’re not already, but one look at all the info in our forums and I guarantee you’ll stick around! We do our best to acknowledge each request made.