Instrument Control (GPIB, Serial, VISA, IVI)

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Feasibility of sending TTL pulses using PC serial port

I accept that this is a long shot, but there are many clever and resourceful folks who use this site, so I'll ask the question in hopes that there is a way. I have device that has several pin ins set to receive TTL inputs to change modes. A HIGH input of > 1 microsecond can switch the mode to the mode associated with that pin. Change modes? Put HIGH to one of the other delegate pins. You get the idea.

 

I have 3 modes I want to switch between, and as I understand it, there are 3 possible transmit pins on a standard serial port connection (pin 3 - data terminal ready, pin 6 - transmitted data, and pin 7 - request to send). Does anyone know of a way to use LabView and a standard PC serial port to send TTL pulses. I suspect the answer is no, especially since the RS-232 standard specifies +/- 25 V? Money's tight and I'm trying to avoid consuming digital outs on my NI-DAQ card. Other clever ideas are welcome.

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This may work, but probably not the way you want and certainly with risk.  First, the serial port does not control a steady TTL signal, instead it sends a series of individual and changing digital bits down a single wire.  Secondly, it doesn't output TTL voltages, which you mentioned.  There could be some workarounds to trying to get this to work...however it's not something we have ever tested here.  There is another forum post on this in regards to the same question below:  

 

http://www.edaboard.com/thread154890.html

 

 

Although your funds may be tight, you can find a low cost DIO TTL device such as the USB-6501 which would accomplish your digital tasks as a true digital device.  Hopefully, the best works out for you in the end.  

 

 

Regards, 

 

 

Ben N. 

National Instruments

Applications Engineering

 

 

 

Regards,

Ben N.
Applications Engineering
ni.com/support
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Think about using the parallel printer port if u have one

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You can control the handshake lines (even the Tx) with the VISA propertynode but timing is software plus OS so it shouldn't be critical.

I would suggest using optocouplers with the RS232 handshake lines. Get the 5V from your device, add pull down resistors (if not already build in).

The current limiting resistors for the RS lines to drive the LEDs of the coupler need a closer look, because the output should stay in the 5mA range and the output voltage of your RS232 device is not so well defined. I would start with 2k and see how it will work out.

 

As already mentioned consider the printerport as an good alternative. More lines, tons of schematics in the web, even ready DIO boars/PCBs available with or without optocoupler /protection/driver. 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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