dmx_basics:dmx_in_practice
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| + | Each physical fixture are set to an address and this address must be the same as the fixture address in the controller.\\ | ||
| + | The address setting for a fixture is so that it will listen on the set address and then the next addresses depending on how many channels the fixture occupies.\\ | ||
| + | How many addresses are stated by the manufacture.\\ | ||
| + | A fixture as shown above uses 12 channels. \\ | ||
| + | This means that if it is set to address 20 then it will receive the values on address 20, 21, 22 … 31.\\ | ||
| + | Fixtures can be set to the same addresses and the fixtures on the same addresses will then do the same think but the fixture has to be the same.\\ | ||
| + | When setting fixture addresses then take care that they don’t overlap.\\ | ||
| + | If a fixture like above starts on address 20 and uses 12 addresses then the next fixture address must be at address 32 to avoid overlapping.\\ | ||
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| + | The maximum no of fixtures in a chain are 32 and his is due to load on the driver circuit.\\ | ||
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| + | The last fixture in the chain has to be terminated with a DMX end or terminator.\\ | ||
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| + | **Why DMX end / termination**\\ | ||
| + | The DMX termination is a 120 ohm resistor.\\ | ||
| + | DMX cable has a characteristic impedance of 120 Ohms. It is a bit complex to be described here but it is a complex high frequency calculation of inductors, capacitors, serial resistors and leak resistors in the cable is self. \\ | ||
| + | The impedance 120 ohm can not be measured with a multimeter.\\ | ||
| + | It is important to terminate the cable with 120 ohm to avoid reflection on the cable which courses the DMX signal to bounce back to the fixture.\\ | ||
| + | The reflected signal may course the fixture to mal function.\\ | ||
| + | See eventually: [[dmx_basics: | ||
| + | Some fixtures has a build in 120 termination that can be activated.\\ | ||
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| + | To build a DMX terminator/ | ||
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| + | Additional for the optimal performance use cable with a characteristic impedance of 120 Ohms.\\ | ||
| + | Microphone cable can be used but for longer distance they may course the fixture to mal function.\\ | ||
| + | The reason is that audio cables has a higher capacitor part in the a characteristic impedance.\\ | ||
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| + | This reflection issue is also the reason for not to split the DMX signal with a Y cable.\\ | ||
| + | Keep it in one line and if the signal are to be divided use a DMX splitter.\\ | ||
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| + | **Why Splitter**\\ | ||
| + | Splitting the signal is the same problem as above.\\ | ||
| + | The load impedance don’t match 120 ohm and this course reflection and DMX signal bouncing forward and backward on the cable.\\ | ||
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| + | The benefit of using a splitter that has building line drivers are that it is possible to have 32 fixtures on all the divided outputs.\\ | ||
| + | And it makes it a bit easier when fixtures are at different places. It is then not a puzzle to get one cable string to all fixtures.\\ | ||
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| + | Finally if it is a optical/ | ||
| + | This eliminate problems with ground loops and spikes when lamps are turned on.\\ | ||
| + | The controller is also protected this way.\\ | ||
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dmx_basics/dmx_in_practice.1325834411.txt.gz · Last modified: 2013/03/11 02:57 (external edit)