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Does the DALI lighting comms protocol require all to have RX/TX capability?

Discussion in 'Radio and Communications' started by Flyback, Jun 11, 2017.

  1. Flyback

    Flyback Well-Known Member

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    Hello,
    Do all DALI connected lamps need to also be able to TX back to the DALI controller?
     
  2. Mosaic

    Mosaic Well-Known Member

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    It's half duplex so it seems so.
    My protocol removes latency compared to the DALI as it places the lighting sequence inside each device which is sync'd via a by a 10mS tick.
     
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  3. Flyback

    Flyback Well-Known Member

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    Thanks, how much current do the lamps need to be able to pull from the DALI bus in order to collapse its voltage down to zero for a pulse (bit)?
    I hear 250mA in wikipedia of DALI but that seems an awful lot?
     
  4. dave

    Dave New Member

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  5. Mosaic

    Mosaic Well-Known Member

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    Well if 250mA is the max permissible drain and 2V is the mas permissible voltage drop for good signalling then you have a drive impedance of 8 Ω
     
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  6. Flyback

    Flyback Well-Known Member

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  7. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    You need to expand your websearching skills.....
    https://www.bing.com/search?q=dali ...1N13ABE91C7D8F5&form=CONBDF&conlogo=CT3210127

    It shows the biphase Tx and Rx protocol with opto isolation .

    Designing a DALI application
    DALI Manual | 08-2013 | en 59 / 93
    Current draw of the DALI circuit
    Each device in the DALI circuit consumes current via the DALI circuit. The total current draw on the DALI circuit must
    not exceed the maximum current of the DALI power supply.
    To determine the current draw of a DALI circuit both the current draw of the DALI devices and the current draw of the
    DALI controllers must be taken into consideration. The current draw of a DALI device is defined in the DALI standard
    as 2 mA. The current draw of the individual DALI controllers (ComfortDIM devices) is shown in the relevant data
    sheets.
    It is important that the current draw of the DALI circuit does not exceed the maximum current of the power supply. In
    the case of DALI-PS and DALI-PS1 this is 200 mA.

    Example: DALI circuit with 24 dimmable ballasts (PCA EXCEL), 3 DALI-GC and 3 DALI-SC
    Current draw of the individual DALI components (from the data sheet):
    Total current = Σ Current draw of DALI devices + Σ Current draw of DALI controllers
    Total current = 24 x ballasts + 3 x DALI GC + 3 x DALI SC
    = 24 x 2 mA + 3 x 6 mA + 3 x 6 mA = 84 mA

    Maximum cable length
    The maximum cable length depends on the maximum permitted voltage drop along the DALI cable; this is defined as 2
    V max. Typically, this requirement is safely met for a cable length of 300 m and a cable cross-section of 1.5 mm².
    Additional voltage drops at terminal points must be taken into consideration. For cross-sections smaller than 1.5 mm²
    the maximum cable length is reduced accordingly
    upload_2017-6-12_1-48-23.png
     
    Last edited: Jun 11, 2017
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  8. Flyback

    Flyback Well-Known Member

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    Thanks ..what none of the websites tell is what current the lamps have to pull from the DALI bus in order to transmit pulses back to the DALI controller....if the DALI is rated to 250mA.....then each lamp must be capable of pulling 250mA from the DALI bus in order to collapse it from 16V to 0V in order to send the low pulse.?
     
  9. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I guess you didn't catch my drift with my searcheresult link... TI chip shows TTL 74LS140 driver and receiver so you can compute current from that chip spec and others in circuit...I hope...

    It seems they only acknowledge the command complete and not detect current with the 2R sense and do not verify the current is actually what the PWM should expect in average current.

    (Although I when did a similar SCADA project in 1978, I actually monitored every incremental or absolute voltage or current setting remotely and displayed within 1 second on a long haul data link HP Computer LED display. 80 column (HP9825) in between frames of 200 sensor values...

    There are more complete schematic examples and code examples if you look hard(er).

    upload_2017-6-12_21-37-31.png
     
    Last edited: Jun 12, 2017
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  10. Flyback

    Flyback Well-Known Member

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    Thanks, this is our DALI TX/RX circuit, but our TX circuit , as you can see, could never draw 250mA from the DALI bus. I will look into you kindly supplied docs.
    The DALI-TX drive voltage is just 2.5V.
     

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  11. Flyback

    Flyback Well-Known Member

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    Also our software guy tells us that in order to implement DALI receiver capability in our lamp, the micro in the lamp needs to..
    1.....have an oscillator running at at leat 16MHz
    2....Have a random number generator function.
    3.....Have the micro reading and writing to EEPROM....this he says is partly because the DALI librarys have to be stored in EEPROM.

    Is any of this correct?
     
  12. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    The bus is intended for hundreds of nodes, so 1 will never do that.
    The other requirements make no sense yet.
     
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  13. Flyback

    Flyback Well-Known Member

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    Thanks, it sounds like maybe you concur with me that 16MHz is way to high for an internal oscillator of a micro thats running simple DALI dimming signals in RX only....(its just a simple dimmable lamp).....DALI is 1200bits/sec, so i think our software guy has made the micro oscillator way too quick at 16MHz?

    Thanks, though there might only actually be one lamp on the DALI bus......we have DALI for our outdoor lamps. but each lamp has its own DALI controller which just broadcasts dimming signals to it.
     
  14. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Not its not that I dont believe the 16MHz its that people who specify without a spec for latency , PWM rate etc and any reasonable RTOS IRQ rate need to be given specs before they can say how to implement it. THe part thats makes no sense is you have no idea of the requirements but you are probably correct anyways that it could be done with less computing power, then then its cheap.

    Say you wanted to sequence commands for continous hue and intensity or RGB at a latency rate of 1 ms with 128 steps then you have a spec.
     
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