Dear who can help,

I am trying to auto-switch the OPTOMA HD25-LV, my new projector at home.
[Link: projectorcentral.com]

So, I buy a usb to RS232 cable (needle, male)
[Link: aliexpress.com]

connect it to the RS232-C in OPTOMA (needle, male)

so, I need to buy another 9-pins to 9-pins (hole to hole, female) cable to connect both male hub.

[Link: ebay.com]
I did so.

I am using Mac, so, I try the Coolterm http://freeware.the-meiers.org/

and sending signal (I can see the usb port in the menu, and setting it as 9600 baud 8N1)

While connect to the projector, it did not pop up any welcoming msg,
also when I typed some text, the greed “TX” is sending signal, while there is no “RX” green light.

So, by seeing the whole process, did I do something wrong? I have spent a lot of time searching the web and find this may be a good solution to Mac user.

While I also tried using Terminal
[Link: pixhawk.ethz.ch]

Hope you can give me a hand on that as you have try to auto switch and control the projector by this. Many Thanks.

PC solutions is also okay, thanks for sharing your experience.

$105 USD for usb to rs232? Why>

oh~ hi ~that just a reference, I got it from my country @ around USD $10 actually.

So, do you know what happens to my control method?any solutions???

If the F-F cable you purchased is a null cable, you likely need a straight-through serial cable instead. Or another null modem adapter.

Try the null modem adapter, does not work also.
Anyway, thank you, Peter.

I've been thinking about this a lot, and there are too many questions that aren't answered in your post.

Firstly, I should say that terminal for sending rs232 commands has been awful since MS pulled HyperTerminal out of windows 7. It was easier before then.

Looking at the manual for your projector: Pg 59 [Link: projectorcentral.com]

We see that Pin 2 is Rx and Pin 3 is Tx. We need to know the exact model of your usb to rs232. Personally, I use the Keyspan USA-19HS which has been fullproof for every device I've ever used it for (except the mid 2000s crestron learner, but that is a different story).

Looking at its manual: Pg 25 [Link: tripplite.com]

I can see that it also use Pin 2 for Rx and Pin 3 for Tx. Right there I know I CANNOT use a straight through cable, I need a null modem. (null modem swaps pins 2 and 3 on each side of the cable). The keyspan has male pins, as does the projo, so I would need a female to female null modem or null modem with gender changers. Just make sure your gender changer isn't also a pin swapper. You may have to pin it out with a continuity test.

What are your commands that you are sending. I assume you are sending ascii and not hex? Are you terminating with a carriage return? Did you set a projector ID code?

Thank you, I think this damn RS232 control pissed me out.
And I would try other method may be manually to control the projector.
What a mess~but thanks for your sincere help.

Haha. Yeah. I have been trying to get two-way rs232 communication with my ~circa 2007 Receiver. What a nightmare. Just trying to find data sheets for it is hard enough, and the one I did find was likely originally written by an engineer from somewhere else and then loosely translated to English. So I understand your 232 frustrations.