Using Arduino as a DMX controlled LED fixture

Projects Networking, Protocols, and Devices
1

Hello all,

I have been working on a project from Instructables for a little while. It is supposed to allow me to control some LEDs with a DMX controller using Arduino. The DMX signal comes in and gets converted with a MAX485 chip, and sends it on to the Arduino. I have been using an off-brand Uno, but I also have a MEGA2560 sitting around. I have built the circuit as the fellow (or lady) who put it together has shown in their instructions, but I have not been able to control the fixture. I am using an ETC Gadget II as my DMX controller. Here is a link to the Instructables page:

I really do appreciate any help that may be offered! I have noticed that my MAX 485 chip has been getting pretty hot when the circuit is on, but I have it wired up based on the schematic. I am also wondering if there is something in the coding that I'm messing up, but the code is using a library from Mathertel, so I have not touched the code.

I tried posting this in the LED section, but I got no reply. I am inquiring as to why I am having problems? There is an error LED programmed in that keeps telling me that I'm not receiving DMX signal, but all my connections match the schematic posted in the instructions. I appreciate any help.

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Looking at the schematic in the instructable, they have wired up the MAX485 incorrectly. They have tied 'RE to ground which enables the receiver. They then also tie RO to ground.

Each time you transmit data via DI, the signal goes out via A & B and also comes back in because the MAX485 is a half duplex device. The MAX485 is then trying to drive the R0 pin which it can't because it's tied to ground.

That would explain why your chip is getting hot.

Disconnect RO from anything and tie RE to 5v to disable the receiver.

Oh, and you may need a new MAX485 chip.

1 Like
3

Hey markd833,

I really appreciate the help! I went back to re-examine and check out your suggestion, but sadly it didn't do what I wanted it to. It got me to thinking though, so I tried setting it up as a receiver (tying RE and DE to GND, and RO going to the Arduino), and it seems to be working. I might still need a new MAX485 as well since I'm getting an occasional signal drop, but this has been a big help whether you know it or not. I wish you the best. Have a good day.