Simple, dumb, RS232 interface

[singlewchildren]

Just a general inquiry, as I have been asked if I can figure out how to use an RS232 port to tell an A/V switch box to either turn off, or turn on.<p>The host is a PC, but the A/V box is an inexpensive device and its eems like overkill to integrate a full blown UART, let alone a micro or a PIC inside the switch box, as there are only two conditions to monitor and respond to.<p>Any ideas on how to make such a brain dead, and of course cheap :-)interface like this work?<p>Thanks<p>John

[jimandy]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>The host is a PC, but the A/V box is an inexpensive device and its eems like overkill to integrate a full blown UART,<hr></blockquote><p>And it also seems like overkill to use a PC to control the A/V box. There must be more to this than meets the eye (or ear).

[philba]

its simple. use one of the other serial signal lines - RTS, for example. Then all you have to do is look at the value of the line. You could use CTS to signal back the state of the device or any other 1 bit of information you want.<p>Phil

[singlewchildren]

"And it also seems like overkill to use a PC to control the A/V box. There must be more to this than meets the eye (or ear)."<p>Yea, it could appear that way, :-)but the PC already exists, and so does the box, so a really simple answer would let him do what he wants. I think he would like to be able to get the box to turn off/on, over a network from a remote location through the PC. Don't really know exactly what the setup is. His question was, can it be done real easy.<p>Thanks,<p>John

[singlewchildren]

" its simple. use one of the other serial signal lines - RTS, for example. Then all you have to do is look at the value of the line. You could use CTS to signal back the state of the device or any other 1 bit of information you want."<p>Hi Phil, I kind of thought about that scenario, but it seemed too easy, so I kind of started going in other directions Thanks for bringing me back to earth and on the simple path.<p>I will give it a shot.<p>Much obliged,<p>John

[philba]

UPSes often use something similar to signal to a Server that power has been lost and its running off of batteries. You can find cabling instructions at the various UPS company's web sites.<p>One thing you should check for coming out of the PC is voltage level. Many PCs output 5V though the RS232 spec is higher. Laptops output 3.3V, iirc.

[terri]

I've used the parallel printer port to control two devices. You send (print) one letter to actuate one device, another letter to activate the other. The two letters must have a one on one selected data line for one device, and a zero on the other selected line for the other device, and vice-versa, for a simple "addressing" scheme.<p>And no UARTS were harmed in the making of this control scheme.<p>Just kind of a hint for other simple possibilites, and you only need one control line... i.e., only one data line on the parallel port need go on or off for your application. <p>If you use the parallel data line 1, for example, you send the letter "A" (0100 0001) to turn it on, and the letter "B" (0100 0010) to turn it off.<p>[ February 01, 2005: Message edited by: terri ]</p>

[Engineer1138]

It's pretty easy: I have an example of controlling a relay from a serial port (schematic + control software) on my website.
You can do it for less than $10 in parts.<p>Actually, based on the number of emails I get because of this one schematic, I think I'm going to put together a parts kit for it.<p>I also have a more complex version assembled, built and tested if you're interested. Just email me at [email protected]

[jwax]

I'll vouch for Engineer1138 circuit! It works!

[Engineer1138]

Hey, thanks for the testimonial

[terri]

I looked those ckts over, and they look darned handy. Beats the heck out of using the parallel port as I did once! Real clever!<p>[ February 02, 2005: Message edited by: terri ]</p>