Summary of PIC18F Based 6 Channel DMX Transmitter
This article details a DIY 6-channel DMX transmitter built around the PIC18F24J10 microcontroller. Designed to test DMX-controlled lights without address adjustments, the project uses assembly language and features six analog channels controlled by potentiometers. It allows for adjustable starting addresses via a DIP switch and connects to an RS-485 bus using a SN75176 transceiver. The device operates on 3.3V logic for the microcontroller and 5V for the oscillator and transceiver, constructed point-to-point on a perfboard.
Parts used in the PIC18F Based 6 Channel DMX Transmitter:
- PIC18F24J10 Microcontroller
- SN75176A RS-485 differential bus transceiver
- 28 pin socket (x2)
- 8 pin socket (x2)
- 10 position DIP Switch
- 3.3v linear regulator (TO-220)
- 16 mhz Crystal Oscillator
- 6 slide or dial Potentiometers
- Female XLR connector (panel mount)
- Male XLR connector
- Resistors: 10k, 100 ohm, 120 ohm, 10 ohm
- Capacitors: 10uF low ESR, 1uF electrolytic (x2), 0.1uF disc
- Perfboard
- Solid strand wire
- 5v @ 500ma PSU
- DC Power Jack (2.1mm)
- RJ45 jack (for ICSP)
PIC18F Based 6 Channel DMX Transmitter
It is written in Assembly and utilizes a PIC18F24J10. A bit odd as it’s voltage input is 3.3v and it requires a low ESR capacitor to ground on one of its pins. I am sure the code could be modified to work on any 18F PIC with a EUSART.
There is no PCB layout, it is easy enough to construct point to point on perfboard.
Please Take a look at AN1076 From Microchip and the PIC18F24J10 Datasheet.
I apologize about my images as my camera decided to crap out with this and another project worth of images on it, so I did my best to recover and recreate them.
*UPDATE:
V2 – Updated the schematic to show the potentiometer hookup.
V3 – PIC Transmit pin was hooked up to the wrong pin on the SN75176, fixed, should be pin 16 on the PIC connected to pin 4 on the transceiver. A pretty big mistake, sorry to anyone that got screwed up by it.
DISCLAIMER: Not responsible for any damage or injuries resulting from this instructable. Damage to DMX Devices is possible if this transmitter is not built correctly.
6ChanDMXTransmitter_v3.zip
Supplies
– 18F24J10
– SN75176A – RS-485 differential bus transceiver
– 28 pin socket
– 8 pin socket
– 10 position DIP Switch
– 3.3v linear regulator, TO-220
– 16 mhz Crystal Oscillator – I used ECS-2200BX-160
– 8 pin socket
– 28 pin socket
– 6x slide or dial Potentiometers
– Female XLR, i use panel mount
– Male XLR, not really needed
– 2x 10 1/4w resistor, R3 & R5
– 100 ohm 1/4w resistor, R2
– 120 ohm 1/4w resistor, R4
– 10kohm 1/4w resistor, R1
– 10uF low ESR cap, less than 5 ohm, but most caps can still work,C1
– 2x 1uF electrolytic capacitor, C3 & C4
– 0.1uF disc capacitor, C2
– Perfboard
– Solid strand wire
– 5v @ 500ma PSU
– DC Power Jack, I used a 2.1mm that matched my 5v power supply. Buy PSU with Matching Jack
-Enclosure, or parts to build one. Tools:
– Solder
– Soldering Iron
– Pliars
– Diagnal Cutter
Layout the Board
I don’t think my layout is optimal. The DIP switch is in an awkward spot which caused a bit of problems when building the enclosure. But overall it is quite small, which was the idea.
Start Point to Point
Make sure that the potentiometer have their voltage hooked up right so the correct direction is value up or down. In my case the pot’s contacts on the bottom of the board was hooked to negative and other end to positive, so when the pots were slid upwards towards the PIC, it increased the DMX value. I did it wrong first and had to go back and fix it. The pot’s center should be connected to the PIC pin, the other to 3.3v(not 5v) and ground.- The Oscillator and the SN75176 require a 5v input and the PIC requires 3.3v.
– Most 3.3v regulators have a different pinout than a 7805, so make sure and find out.
– The male XLR receptacle is not required or is the ICSP jack.
- What is the primary function of this project?
To demonstrate a simple DMX transmitter that tests DMX controlled lights without adjusting their address. - Can this code work on other PIC microcontrollers?
The code could be modified to work on any 18F PIC with an EUSART. - How is the starting address adjusted?
The starting address can be offset via a 9-position DIP switch. - Does the PIC require a different voltage than the transceiver?
Yes, the PIC requires 3.3v while the oscillator and SN75176 require a 5v input. - What type of capacitors are required for the PIC?
A 10uF low ESR capacitor with less than 5 ohm impedance is required on one of its pins. - Is a PCB layout provided for this build?
No, there is no PCB layout; it is designed to be constructed point to point on perfboard. - What is the purpose of the RJ45 jack mentioned?
The RJ45 jack is for ICSP and is not necessary for operation. - Which pin on the PIC connects to the transceiver?
The PIC Transmit pin should be connected to pin 16 on the PIC and pin 4 on the transceiver. - How are the potentiometers wired for correct value direction?
The pot center connects to the PIC pin, one end to 3.3v, and the other to ground. - What tool is needed to build the enclosure if not using a pre-made one?
You need parts to build an enclosure along with solder, a soldering iron, pliers, and diagonal cutters.
