Using DB9 as a remote?

[jofruit]

Hello Everyone,

I have a quick and (hopefully) simple question about DB9 controllers.  I would like to have a DB9 connect into a Leybold Turbo Controller 700.  I was told by the company that although the back of the box looked DB9, it establishes and tells the controller to start/stop based on electrical signals, not really transmit/receive connections.  I was told the following:

Pin 7- 12V

pin 6- GND

pin 8- Start/Stop Signal (power 8 b/t 11-26V for system to start; remove power and it should stop)

3 & 4 are common

My main question is this: If I plug my DB9 straight cable into my computer and the control box, is there a capability to assign voltages to particular pins or is this difficult/impossible to do?  Should I be building some sort of relay using a NI DAQ?  What does everyone recommend?  Thank you.  Below is a pin picture I beleive, but I received these details from the company and wanted to ask this question on the side.

[crossrulz]

The DB9 that is on your computer is an RS-232 port.  It will NOT do what you want.

What I would do is find a Digital IO card from NI and make it control a relay.  The relay will apply whatever voltage you want to the pin 8 or disconnect the voltage (when off).

[Hooovahh]

Why is this type of request so common?  Do people expect they can turn on and off pins on an RS-45 connector generally used for ethernet?  I realize that there is some control over printer ports being able to be pulled high or low but when was the last new computer you bought that came with a printer port?

[SteveD123]

Yes, but you could use the DTR handshake line if attached to a suitable high impedance opto isolator.

Gets the job done without buying any hardware.

[SnowMule]

Doable with the status lines on the serial connector? Absolutely.
Recommended? Nope.

Get a cheap digital I/O board (like a USB-6501) and some power/signal drivers, then go from there.

[jofruit]

Thank you for the comments so far.  I have a question regarding the hardware that you suggested.

Under specifications it says that the range is 0-5V.  Does this mean that the maximum acheivable voltage is 5V?  The pins need to be powered by at least 12V right?

[johnsold]

DB-9 is simply a connector. There is absolutely no rule which says what ust be wired to that connector.  On your computer it appears to be wired to an RS-232 port. This has well-defined voltage and timing specifications to allow communications with other RS-232 equipment.  On the other device it seems to be wired to several power and control signals which are customized to that device and are clearly NOT RS-232 compatible. If you plug this device into the RS-232 port (which happens to use a physically compatible connector), at the best it will not work. At worst you could destroy both the external device and the computer.

Lynn

[NIquist]

I think he's asking about the 6501.  If so, you're correct that it will not drive your signals directly.  It is a TTL device so +5V and 0V are the only possible outputs.  You will need an external driver circuit to convert the TTL into the 12V required by your device.

[Dennis_Knutson]

Or use a digital line to drive a relay like is shown in your schematic.