28 Ch DMX Air Controller

DMX Air Interface

This will detail a 28 channel DMX air control system I Made to control several props in my haunt from one central location. It uses a custom DMX control board to address each air valve using four parallax SX chips with a buffer chip and can be controlled using Visual Show Automation. This would also work with vixen and many other show control Software’s. I purchased several Solenoid banks each with 8 valves, these were controlled from a DB-25 Terminal after a few designs I ended up with this as the simplest was to address and control them all in my setup. This control box could also be easily adapted to control relay packs as well, all it would require is a new cable to be made. I am working on designing the relay pack to allow control of lights or other devices.

Plastic Enclosure
Custom DMX Board
24 Volt power supply
5 Volt power regulator
RJ-45 Keystone blocks and cases
Custom Cables to connect the solenoids
8 channel solenoid blocks
DMX cables
Power Cable

Enclosure/Status LED’s/connectors:
I ordered a weather proof plastic enclosure that would be large enough to house the control board and power supplies. Any box will do as long as it is big enough to hold the electronics. I set all the major components inside the box to figure out where they would fit best, once that was done I marked where the holes would need to be drilled for mounting later on.

I added six External LED’s to provide a status on the control signal. Four show the status of DMX signal moving thought the box and two for power. The signal LED’s each have a resistor installed and one wire running back to the main control chips and the others are tied together and connected to a ground point. This will indicate when a DMX signal is received.

There are several external connectors for this control box. The first is 120 Volt for the power supply, Second is two XLR cables, These provide an input and output for the DMX signal and four RJ-45 Jacks used to connect the output’s.

DMX Control Board and external connectors:
This control box uses four of the custom DMX boards that I have used for a lot of different projects though out my haunt. They are easy to make and have a fairly low parts count. I built four of these circuits on a single board to make the system a little simpler. The DMX signal is daisy chained from the four transceivers with two screw terminals for the DMX In and DMX Out. The power is combined for all the of the micro-controllers and chips this comes out to a single screw terminal for the power input. There are also screw terminals for the status LED’s that are installed in the case.  To allow the micro-controllers to switch a 24 volt valve I used four ULN2803 chips. These protect the MCU and allow the higher voltage to be switch with out an issue.

To make the box easier to store I added 4 connectors on the outside of the case for connection to the custom cables that will connect to the air valves. The connectors are RJ-45 Keystone blocks in mounts that each hold two of the connectors. This modular design allows the box to be removed or different custom cables to be adapted to the design. The last connectors are 4 RJ-45 Keystone blocks, Each one of these connects to one of the valve banks in the haunt. I used pin headers on small pcb’s to connect each RJ-45 terminal to one of the ULN Chips. They are setup to allow the board to be easy to remove if I upgrade it. They each carry seven output signals and a ground.

Power supplies and regulators:
This control box only required two power supplies, It has a reused industrial power supply to generate 24 volts for the valve banks and a 5 volt power supply for the DMX circuits. They are both connected to the 120 volt power cord. This will provide all the power that is needed by this unit. Since 24 volts is fairly universal in a lot of automation it easily allows the control box to run different devices after the connection is changed.

Custom Cables to connect the valve banks:
To connect each of the solenoid banks back to the main control box I made up 4 custom cables. These are RJ-45 on control box side and DB-25 on the valve side. I limited each bank to 7 valves to allow me to use a single CAT 5 cable to make the connection. 7 control wires and 1 ground wire. I made each cable long enough to place the valves a good distance from the main control box. To make these I simple crimped RJ-45 Ends on the first half of the CAT-5 Cable and on the other side I soldered to the correct pins to make the ground and control each of the 7 valves. These cables could be re-done to control almost any 24 volt solenoid system.

Once installed I was able to run 4 separate scenes from one control box and it functioned all night with out any issues.



If you need some more information Email me