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When I search for RS485 board (to be used for my Arduino to control DMX512), I find mostly two types:

  • GPIO / TTL based (which I want to use), like TTL RS485, which mainly has a MAX485 and some resistors/capacitors. This one works with DMX512. enter image description here
  • UART based, like UART RS485, which has also thermal/polyfuses and TVS protection. This one I don't want to use because I want to use UART for other purposes.

enter image description here

Would it be useful to recreate the GPIO based version, with additional polyfused/TVS circuitry?

I cannot find a GPIO/TTL based version with more protection, why is this?

(note I will only use RS485 (DMX) output, not input).

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    \$\begingroup\$ I don't understand the difference. Both look like TTL UART to RS485 converters. Or is the other device a RS232 to RS485 converter? Regardless of TTL or RS232 voltage levels, these are using UART serial transmission. \$\endgroup\$ – Justme Jul 5 '19 at 13:08
  • \$\begingroup\$ @Justme I'm confused about the boards (too) ... the UART shows clearly RXD/TXD, the other shows DI/DI/RE/RO. \$\endgroup\$ – Michel Keijzers Jul 5 '19 at 13:10
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    \$\begingroup\$ The ones with RXD/TXD is also TTL to RS485 converter. It just has "automatic" flow control whatever that means and depending on how it works it may or may not suit for a certain application. Most likely it enables transmitter automatically for some time period when it detects transmission from TTL side. \$\endgroup\$ – Justme Jul 5 '19 at 13:16
  • \$\begingroup\$ I ordered both of them, than I will check if the second works and use that one (because of the better protection). \$\endgroup\$ – Michel Keijzers Jul 5 '19 at 13:16
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    \$\begingroup\$ Chances are you can modify it to disable automatic detection and force transmit only mode for DMX512 output. Or create own board with interface and protection you want. Frankly, I would just buy the DMX shield if the point is to have DMX on Arduino. \$\endgroup\$ – Justme Jul 5 '19 at 13:30
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They are both RS485 tranceivers, just different. There is no "why" we can answer why these are like they are. There are applications that require different TTL interfaces and sometimes different level of protection is needed on the RS485 side. They might still use the same RS485 tranceiver chip at the core.

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  • \$\begingroup\$ Ok ... than I take the one with better protection since I will use many external DMX512 fixtures (lights) to be connected.Or I reverse engineer the thing and integrate it to my PCB I want to make. \$\endgroup\$ – Michel Keijzers Jul 5 '19 at 13:30
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For the first module you have to handle the data directions by setting up DE(driver enable),RE(receiver enable)pins and RO for RX(receive) and DI is for TX(transmit). Connect RE,DE to a one GPIO and then set it to HIGH to put the module into transmit enable, put it to LOW for receive enable.

For the second module you don't have to do the enabling part it is automatically done by the additional circuit available in it(74HC04).

If you are designing a circuit for a industrial environment it is wise to use TVS diodes and poly fuses as in second module, but if you are doing a hobby project first module is sufficient.

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Check this circuit diagram from XY-017 RS485 schematic

enter image description here

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