LEDs on Mendel90

I'm wanting to hook some LEDs up to my Mendel90, but I'm stumped when it comes to where to hook them up. I have the Melzi board that comes with the kit. I'd like to connect the LEDs to the Melzi, but also (if possible) control the LEDs through the use of 'printer interface' commands. If I have to, I'm fine with the LEDs being on all the time if the printer is powered.

Are the 2x3 and 2x5 connectors next to the USB connector usable? As in, power through those and control through the use of commands? I thought about connecting the LEDs to the fan port, but there are times when I want the LEDs on and the fan off. Any other options out there?

You can get 12V from the unused fan connector terminal as the fan shares the 12V feed for the heater and you can get 0V from the expansion headers.

You will need to add a MOSFET and control it from one the spare digital lines on the expansion port if you want software control. Similar to what I did here, but not the same pins [hydraraptor.blogspot.co.uk].

Also the Panalolu2 LCD add on for Melzi adds anothe fan drive I think, which could be used for LEDs.

Edited 1 time(s). Last edit at 06/01/2013 12:52PM by nophead.

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[www.hydraraptor.blogspot.com]

Panelolu2 has two FETs, controllable via the M42 command. I have one controlling the bed fan, and am thinking of wiring up some LEDs to illuminate the bed on the second one, probably in conjunction with my "present work" command.

Don't forget your current-limiting resistors!

A rather simple way would be to remove the 10 ohm resistor that is on the 5 volt(red) line and replace it with LEDs with appropriate series resistors.

Better to leave the resistor and add the LEDs plus resistor in parallel. The more load on the 5V rail the better.

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[www.hydraraptor.blogspot.com]

Seems right - the 12 volt line measures a fraction high. Some suppliers seem to provide the ATX power supply without any dummy load - I haven't really examined how important an extra volt or half volt might be.

It will be high when the bed is off and lower when it is on. The power in the bed is proportional to V squared so you want it to not drop much below 12V.

Over voltage is not an issue for the machine but it can cause the PSU to shut down.

These are very cheap PSUs. You can pay 10 times more for a good one with proper regulation on each rail.

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[www.hydraraptor.blogspot.com]