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Questions regarding circuit using jm_dmxout.spin by Jon Williams — Parallax Forums

Questions regarding circuit using jm_dmxout.spin by Jon Williams

skylightskylight Posts: 1,915
edited 2013-05-02 10:54 in Propeller 1
This is a very elegant and simple object to understand programming wise
I have a few questions about the circuit itself
the questions relate to what I believe is the last updated version: 23 SEP 2009
diagram is as below:


+5v           +5v
                              
                │             │
                             │                   
            4k7 │ ┌─────────┐ │                   
   dmxrx ────┻─┤1°      8├─┘                   
    txrx ──────┳─┤2       7├────────┳──────┳─────── Pin 2 XLR-F 
                ┣─┤3       6├────────┼─┳────┼─┳───── Pin 3 XLR-F    DMX OUT
   dmxtx ──────┼─┤4       5├─┐      │ │    │ │ ┌─── Pin 1 XLR-F 
                │ └─────────┘ │      │ └ ┐  │ │ │               
            4k7    ST485BN   │  120  ┌ ┘  └─┼─┼─── Pin 2 XLR-M
                │             │      │ │      └─┼─── Pin 3 XLR-M    DMX IN
                                   └─┘        ┣─── Pin 1 XLR-M
                                                └ ┐
                                                ┌ ┘
                                                

Regarding the two resistors top left attached to pin 1 of the ST485BN i'm presuming they are both 4K7 as there is only one designation, is this correct?
The diagram above is one of two I found on the OBEX the previous one (older version) I believe (mislaid this and can't find it) showed a 10k ohm in the 5v line to pin 1 so is the latest version diagram missing this or are both resistors 4K7 as presumed?

The 120 ohm resistor is shown with a symbol that looks like a removable link is this showing a link or does it mean use on long length of cable? I ask as normally the 120 ohm resistor is an end of line resistor, so should that be across pins 6&7 or is it saying attach at end of cable run from the XLR? If not wouldn't it terminate and drag down the signal out from the ST485BN pre the XLR?

Again the same "link" symbol is shown on the screen to Gnd cable from pin 1 of the XLR , what does it denote?

I notice no resistor shown on the prop pin to pin 4 of the ST485BN (there is one in line with pin 1) as the chip is supplied with 5v is it safe to connect pin 4 directly to the prop i/o without a resistor? Same with prop to pin 2&3?



Thanks in advance for clarifying

Comments

  • PublisonPublison Posts: 12,366
    edited 2013-04-30 03:32
    That looks like the circuit from Jon Williams Spin Zone article #3

    The jumpers are explained in the article. The correct resistor are also listed.

    The complete "Spin Zone" listing is here
  • skylightskylight Posts: 1,915
    edited 2013-04-30 04:04
    Thank you Publison
    I didn't realise there was this resource existing
  • JonnyMacJonnyMac Posts: 9,107
    edited 2013-04-30 04:16
    As the artist formerly known as Jon Williams, I can probably help out.

    I used 4.7K resistors all around to simplify the BOM. The pull-up on the RX line keeps it at idle when the device is in TX mode (which floats the RX output of the chip). The series resistor into the Propeller RX pin limits current as that chip has a driven output when in RX mode. The pull-down (on pins 2 and 3) keeps the device in RX mode when that Propeller control pin is floating -- you have to [deliberately] drive that pin high to put the chip in TX mode. The chip is a 5v device and does not need a current limiter into the TX pin. It won't hurt to put a resistor in the TX line but it does not help anything, either; pin 4 on that chip is an input so there would never be an electrical conflict between it and the Propeller

    The 120-ohm line terminator is required at the ends of an RS-485 link to prevent reflections; the jumper allows you to move nodes in a system and enable line termination if the node is at one end of the line or the other. See this link:
    -- http://www.maximintegrated.com/app-notes/index.mvp/id/763

    I have used that circuit many times -- it works really well for half-duplex, RS-485 applications.
  • skylightskylight Posts: 1,915
    edited 2013-04-30 08:40
    Thanks JonnyMac, I'm looking forward to getting the chip and having a play.
  • skylightskylight Posts: 1,915
    edited 2013-04-30 09:47
    I've read through the very interesting article and am impressed with the build quality of the driver board shown in the article.
    Looking through the Gadget Gangster site i'm unable to locate the kit and wondered if it is still available from somewhere?
  • PublisonPublison Posts: 12,366
    edited 2013-04-30 10:16
    skylight wrote: »
    I've read through the very interesting article and am impressed with the build quality of the driver board shown in the article.
    Looking through the Gadget Gangster site i'm unable to locate the kit and wondered if it is still available from somewhere?

    Nick from Gadget Gangster has been off the radar for a while.

    The original Platform that JonnyMac created is in Column #0, (ExpressPCB)

    The ExpressPCB files were included in the DMX article.
    zip
    zip
    nvp3.zip
    5M
  • skylightskylight Posts: 1,915
    edited 2013-04-30 11:49
    Thanks Publison, I did see the files but was wondering if the kit was still available.

    Express PCB is out of the question at $135 for two boards, that's without silkscreen and solder mask
    $311 with!!
  • JonnyMacJonnyMac Posts: 9,107
    edited 2013-04-30 12:51
    The circuit is very simple and you could use ExpressPCB as a routing reference to move the board to DipTrace (what I'm using now) or Eagle or any other program you choose. That said, once you move the schematic to your favorite program you can make a board any way you like. If I was to do that board today I would make it compatible with the QuckStart.
  • skylightskylight Posts: 1,915
    edited 2013-05-01 07:47
    Thanks JonnyMac, I wasn't aware that you can export from ExpressPCB to Diptrace, I thought it was done deliberately in order to force the user to use their manufacturing process, I shall give it a try and then perhaps see if I can find a cheap pcb manufacturer.
  • JonnyMacJonnyMac Posts: 9,107
    edited 2013-05-01 22:41
    To my knowledge there is no export facility in ExpressPCB. You could do a screen cap of each layer from ExpressPCB, trim the graphic, then pull it into DipTrace on the assembly layers. That said, this is such a simple circuit it's probably best just to build the circuit and pcb in DipTrace from scratch.

    I can't do it right away, but I will probably convert this to QuickStart format as I do a lot of work with DMX.
  • skylightskylight Posts: 1,915
    edited 2013-05-02 08:37
    I'll have a go at creating it in Diptrace, I look forward to seeing the Quickstart version.

    The hardest thing is getting compatibility with other boards plugged into the Quickstart, for my project I'm already using a QMP touchscreen, obviously this would have to be the top board in the sandwich It leaves pins 8-15 free for use with the DMX board which would have to be the middle board so would need pins below with female header above, do they make female headers with long pins that could pass through the middle board and plug into the Quickstart?

    The Quickstart does have alternative pinouts that can be soldered to so perhaps the dmx board could end up underneath the quickstart?

    I'm trying to keep the quickstart footprint for compactness, would be nice to keep the height as low as possible too as batteries need to be added also, been looking at the 18650 format to give 7.5v which I would regulate to 5v to feed the DMX and Quickstart boards..
  • JonnyMacJonnyMac Posts: 9,107
    edited 2013-05-02 10:54
    When I assign pins I will have a look at other QS shields and do my best to prevent conflicts.
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