Hi, i have a problem.
A have pro mini and it´s connect via max 485 to DMX device. It connected for one second and then disconect. When i reset (unplug and plug to usb) it ´s repeat (connect for one second und disconect) Why? please help me :slight_smile:

I use MAX 485, 100 Ohm, And pin 3 :slight_smile:

Pins 2 and 3 should both be either pulled high, or pulled low, depending on whether you want to transmit or receive. right now you have told the chip to enable both, which is probably causing logic problems. In your case it looks like you are trying to transmit, so both pins should be pulled high. I have also had problems with 485 chips that didn't have a .1uf decoupling cap near them.


I use this code:

#include <DmxSimple.h>

void setup() 

void loop() 
    DmxSimple.write(1, 255); 

And image:

The red led (DMX on picutre 2) is black. It should lighting when dmx is connected .

And video:

The DMX LED blink when i plug cabel to arduino (pin3), and then is dark.
I repeat this and it´s same.

I use mega 2560 for easy access, because pro mini must have a converter.

When i put Serial.begin(25000); in to the code, and cable to TX pin, DMX lighting on LIGHT but, it not working with arduino code

And when i use dmx serial then it works but i musn´t change code because then it isn´t worknig .

To : ld3300: I try: pinMode(2, OUTPUT); pinMode(2, INPUT_PULLUP); … nothing

Did you do as ld3300 suggested and also connect pin 2 of the SN75176 to VCC instead of ground?

The data sheet looks like 2, 3, and 4 need to vary between HIGH and LOW depending on whether you receiving or transmitting and depending on what you are transmitting.

It looks like in your schematic that 2 is always LOW (connected to GND) and 3 is always HIGH (connected to VCC). If 3 is always HIGH, it looks like varying 4 will vary the outputs on 6 and 7.

Maybe you could show how the MAX485 is connected?

I am entirely unfamiliar with how the DMX protocol is handled. Maybe if you talked through it (and gave us a lesson at the same time- hint, hint) it would help you solve the problem?

The 100 ohm termination resistor goes between pins 6 and 7 (but can be
omitted if only ever transmitting and not receiving, as for simple DMX). It
doesn't belong on pin 1.

DMX has no notion of connected or disconnected, you just blast packets out
all the time.

I try everything what you say, byt it´s still no working. But when i try this:

and use Libreria DMX librarie then it works. ? :astonished: