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DMX Analyzer
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.
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.
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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 100µF 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.
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 |
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 |
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: 176µs - 352µs
MAB: 12µs - 88µs
IB-Gap: <32µs
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.