I am trying to replace the lamp and ballast assembly in an Acer P1500 DLP projector. The ballast is an OSRAM PT-VIP-05 COMPACT. It features a UART control scheme that allows the motherboard to query and set various parameters intelligently. I've been able to find the datasheets for both the ballast module itself as well as the specific protocol it implements via the UART. The issue I'm having is that I can't quite figure out how to "reverse" the weird way that the Tx and Rx lines are sort of split for lack of a better explanation.

This is the schematic, per the OSRAM datasheet:

OSRAM Lamp Driver Control Board

I need to replace the left hand side of the schematic with an Arduino or similar, the code and wiring and such I can absolutely handle. What is giving me trouble is correctly getting the Tx and Rx lines to neatly convert to the "standard" 3-pin UART interface we all know and love (GND / Tx / Rx).

Can anyone help me make sense of this?

For additional reference, I did find some information here but the forum is in Russian and there's a lot lost in translation I think. There are also some hints here, and here.

Those pages reference the datasheets for the OSRAM Standardized UART Protocol as well as the OSRAM 5-Pin Interface, both of which I've uploaded in case they're helpful to anyone who needs them or is willing to help.

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    \$\begingroup\$ The circuitry on the left has signals labeled "TDO" and "RDI" which correspond functionally to TX and RX. There is also a ground symbol. Can you be more specific about what you don't understand? Can't you just replicate what is on the left as an interface to an Arduino? \$\endgroup\$ – Elliot Alderson Jan 15 '20 at 0:35
  • \$\begingroup\$ Your latest links report "You are not authorized to download this file" when I attempt to open them. With that said: Can you share more specifically what you don't understand? It seems that the circuitry is almost fully shown, just requiring a few passives and so on to interface to 5V voltage levels reliably. Since some other crucial values are missing (e.g. the values of R1/R2 on the right) it will be hard to compute exact values to be used. \$\endgroup\$ – nanofarad Jan 15 '20 at 0:38
  • \$\begingroup\$ You need to add all of this information to the question itself...don't bury it in the comments. Also, your links do not appear to allow public access. \$\endgroup\$ – Elliot Alderson Jan 15 '20 at 0:39
  • \$\begingroup\$ @ElliotAlderson - I was typing out the additional comments when you responded, my apologies. What I don't get is that they don't appear to actually function that way at all. The UART interface is supposed to operate at 9600 8E1, and any interaction from the projector main board should begin with 0x00 followed by 0x70 (a sort of "wake up" and "enable communication" respectively). When I hook up the Tx / Rx / GND lines as you'd expect, I get nothing. When I attempt to replicate the strange Russian circuit from the link, I don't get the right values. \$\endgroup\$ – Mark Schlachter Jan 15 '20 at 0:39
  • \$\begingroup\$ What do you see when you check the lines with an oscilloscope? \$\endgroup\$ – Elliot Alderson Jan 15 '20 at 0:41

I need to replace the left hand side of the schematic with an Arduino or similar

This statement does not make any sense. The left side of the schematics is just an interface, you do not "replace" it, you connect "Arduino or similar" board to it. After making sure that voltage levels are compatible, of course. But that is a simple task of choosing correct optocouplers and adding resistor to TDO line.

The only thing that might require a bit of tweaking is the signal polarity. But even that can be sometimes resolved in software since many MCUs have "inverted" bits in UART control registers.


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