DIY DMX shield

[dodger]

I have built my own Arduino DMX shield. Unfortunately I could not find
the exact transceiver chip that you have used in the tinker It
schematic. Rather then the MAX-485 or SN 75176 I am using the RS 485
from National semiconductors. My circuit is identical to the one on
tinkerIt but my DMX dimmer pack seems to not be receiving any signal
at all. I have double checked the pin connections to make sure they
are correct. (I am running the fadeUp test code)

Is it possible that these chips are not up to the job or is there
something basic that I am missing?

[Peter Knight]

On Sep 11, 1:21 pm, dodger <davidmcgo...@gmail.com> wrote:
> I have built my own Arduino DMX shield. Unfortunately I could not find
> the exact transceiver chip that you have used in the tinker It
> schematic. Rather then the MAX-485 or SN 75176 I am using the RS 485
> from National semiconductors.

National Semiconductor don't make a chip called 'RS 485'. Can't help
you verify the electronics unless you accurately describe the chip you
are using.

> My circuit is identical to the one on
> tinkerIt but my DMX dimmer pack seems to not be receiving any signal
> at all. I have double checked the pin connections to make sure they
> are correct. (I am running the fadeUp test code)

Have you set the DMX address on your lamp appropriately?

Have you customised fadeUp to your lamp? Check you are sending out
enough channels, and check that any 'shutter', 'brightness' or 'mode'
channels are set appropriately.

The DmxSimple software is well tested and is known working - so I
would concentrate your efforts on your wiring, interface and DMX
setup.

> Is it possible that these chips are not up to the job or is there
> something basic that I am missing?

Most RS485 compatible driver chips will work fine. Some chips have
reversed outputs, but that can be solved by switching over the two DMX
data lines. Give me the correct part number of the chip you are using
and I'll verify its compatibility.

[david mcgoran]

Ops your right the chip is actually a DS485 low power RS-485/rs-422 multipoint transceiver from National Semiconductor. Looking at the data sheet I see no reason that it can’t be a good substitute.

 

I ma trying to control a 4 channel DMX dimmer pack, where I have a standard lamp plugged in to the kettle socket.

 

I have set the DIP switches on the pack so that CH1 is the first out let on the pack.

 

I have gone through the wiring many times and can not see an error.

 

The DMX dimmer pack is working as there is a test setting and it is capable of lighting lamps from all 4 sockets.

2009/9/11 Peter Knight <cath...@gmail.com>

[Peter Knight]

Okay. I concur, for these purposes the DS485 is equivalent. So things
you should do:

1) Check dimmer manual for its DMX input spec. You should verify that
you are sending out all the channels required, and they are the
correct value. Some multi-channel receivers will not receive unless
you send all the channels, even if you are only using the first. There
may be a 'mode' channel that needs to be set.
2) Check wiring on the DMX socket. DMX is a mess for wiring - 5 pin, 3
pin, reversed polarity, different pin pairs... So check your DMX
dimmer manual, make sure you are poking the right signals on the right
pins.
3) Try swapping over the two data lines on the DMX connector.
4) If you are using a long cable (several metres), try a shorter one
first.
5) If you have another DMX lamp or controller, try swapping around to
isolate the problem.

One other thing. What board are you using? Is it an Arduino? A clone?
Does it have a 16MHz crystal?

[david mcgoran]

OK great I’ll look in to this further

I’m using a standard Arduino diecimila with a 16MHz crystal

I’m using basic 3 way sound cable not 5 way

 

I was assuming that the DmxSimple was using interrupts and therefore the clock speed was not a problem…I was hoping to use a 3.3VArduino pro minis that have a clock of 8MHz…..or is the 16MHz vital?

2009/9/11 Peter Knight <cath...@gmail.com>

[david mcgoran]

 

Fantastic!

Its all up and running now

Unfortunately I could not identify the cultrate

I built an entire new circuit form scratch, new chip and all

Maybe a loose wire or damaged chip?

Thanks for you time

 

Hope to take the next DMX workshop..

D

2009/9/11 david mcgoran <davidm...@gmail.com>

[Peter Knight]

DmxSimple has some time critical code in it. It will work on any clock
frequency, provided GCC is passed the clock frequency with a F_CPU
define. This will be handled automatically by the Arduino build
process for all Arduinos, but that is something I can't guarantee for
all clones.

Provided F_CPU is correct, the only timing constraints are: The clock
frequency must be at least 4MHz, and must be a whole number of MHz.
The only clock frequencies you're likely to find in the Arduino world
are 8MHz, 16MHz and 20MHz. They all meet this requirement.

If you are going to use 3.3V, check that the RS485 converter you are
using is compatible with 3.3V power and data. Many are not.