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DMX Analyzer

This firmware was designed more for "DMX freaks" than for ordinary users. With the help of the analyzer, the signal of DMX consoles or PC interfaces can be evaluated and checked for compliance with the current standards.

 

In addition, the analyzer can transmit various reference signals in order to detect weak points in receivers such as dimmer packs or moving lights.

The analyzer consists of a DMX Transceiver and a 2x16 char Text-LCD (HD44780 compatible). Three push buttons are used as user interface.

 

Rev. 3.2

DMX Transceiver (Rev. 3.2)

With this module, DMX data can be sent and received. However, due to using a microcontroller, this circuit is not ideal for beginners.

The Transceiver is suitable for bidirectional communication (e.g. RDM according to ANSI E1.20) due to the complete connection of the RS485 converter.

Industrial-quality circuit boards are available in the shop.

 

 

 

DMX-Transceiver schematicpart list

  IC1
  IC2
  IC3
  D1 
  LED1
  LED2
  R1
  R2,3,4
  C1,2
  C3,4
  C5,6
  SW1
  Q1
  connectors
ATmega8515-16PU (+socket!)
75176B (+socket!)
7805
1N4007
LED 5mm red
LED 5mm green
10k (PT10-S)
390 Ohm
27pF
100nF
100F
DIP switch (10x)
8MHz (HC49)
pin header RM2.54

 

 

 

 

 

 

 

 

 

 

 

 

As you can see, the circuit is quite simple: All the magic happens in firmware within the MCU (IC1). It is transferred to IC1 via the "ISP"port. The start address and special options (if any) are set via ADR. The LEDs serve as status indicators. The voltage regulator IC3 ensures a stable operating voltage of 5V. Q1 and C1,2 are needed for an operating frequency of 8MHz. The RS485 converter IC2 allows the MCU to communicate with the DMX universe. With the help of "Spare", various firmware options can be jumpered. Via A-Input, an analogue threshold value (e.g. for thermal protection) can be read.

A supply voltage between 9V and 12V dc is connected to PWR. The DMX Transceiver itself requires <300mA. When selecting the power supply, all loads must be taken into account.

pcb layout (48 * 76 mm^2; 300dpi)

placement

The transceiver is connected to the DMX bus as shown in the next diagram:

Attention: Pin 3 of the XLR connectors is connected to the middle pin of the PCB connector!

 

Instructions for programming and selection of clock sources can be found under 'Resources'.

After changing the clock source, the Analyzer firmware can be transferred to the DMX Transceiver.

 

LC-Display (HD44780 compatible)

The LCD is connected to the output of the Transceiver using the following table. The pin assignment of the LCD can be found in its data sheet.

LCD Transceiver Signal
D4 Out1 (PA0) data
D5 Out2 (PA1) data
D6 Out3 (PA2) data
D7 Out4 (PA3) data
RS Out5 (PA4) register select
E Out6 (PA5) enable
Vo GND contrast
R/W GND read / write
GND GND ground
VCC VCC +5V

 

Push buttons

The analyzer is controlled by three buttons that pull the SPARE inputs to GND: 

Transceiver Function
SPARE1 (PD4) Mode
SPARE2 (PD5) Up
SPARE3 (PD6) Down

 

How it works

DMX Timing

In this mode, the timing of the incoming DMX frames is measured. A new frame is indicated by a Break, in order to synchronise all receivers. This is followed by a Mark After Break to clearly distinguish the break from the subsequent start byte. After the start byte the individual channels are transmitted. Between individual channels, many transmitters wait a few microseconds in order to give poorly designed receivers time to process data. This delay is called an inter byte gap or inter slot time. According to the standard E1.20 the following timing is permissible:

Break:  176s - 352s
MAB:    12s   - 88s
IB-Gap: <32s

Universe State

In this mode, the size of the universe and the refresh and error rates are measured. The refresh rate should be above 20Hz. A maximum of 512 channels are allowed. If a break occurs and the following start byte is neither 0x00 (DMX) nor 0xCC (RDM message), this is considered an error.

 

DMX Overview

10 consecutive DMX channels are displayed as a bargraph. The Up/Down buttons can be used to select the section being viewed.

 

DMX Input

The values of two consecutive DMX channels are displayed. The channels can be selected with the Up/Down buttons.

 

DMX Output Slow

512 channels are faded up and down. The transmission is slow with a very long break and inter byte gaps.

 

DMX Output Fast

64 channels are faded up and down. The output is very fast with minimum allowable break time and no inter byte gaps.

 

DMX Output Val

512 channels with the set value are transmitted in slow mode.