Line connection between PCI-6527 card and instrument

Question

Sorry for my foolish. My poor electronic knowledge prevent me from fully understanding what you explained in your last reply and need more help.
In fact, we plan to control two instrument switchs, one is for the Magnetic_Suspension_Control(MSC) , another is for control the Weight-changing-Device(WCD).
The instrument manufacturer provide a cable for the MSC and WCD. The cable looks as follows: there is one connection to the computer(25-pin subD-plug) of which two cables lead away, one to the MSC(6-pin Lemosa)and the other to the WCD(15-pin subD-plug).
The interface of the MSC is internally realized by using only two simple optocouples(OC). Their input-pins are connected directly to the 25-pin SubD-plug of
cable as follwing:
25-pol.SubD; meaning
Pin 9 anode of OC1-LED
Pin 7 anode of OC2-LED
Pin 23 cathode of OC-LED
Pin 18 cathode of OC-LED
Because of the optocouplers draw some current from the NI-card, the manufacturer let me make sure that the NI-card can source circa 7mA(better 10mA) on each pin.
The interface of the WCD consists of three simple TTL-level inputs, which are also directly connected to the 25-pin SubD-plug of our cable as following:
25-pol.SubD; meaning
Pin 4 TTL-Input (remote) (0-1V/3.5-5V)
Pin 3 TTL-Input (weight 1) (0-1V/3.5-5V)
Pin 2 TTL-Input (weight 2)(0-1V/3.5-5V)
Pin 5 common ground
The current drawn by the TTL-inputs is not worth mentioning.
By controling the logic state of these above pin states through labview, I then can control the instrument switch.
Based on above information, how should I choose right resistor for achieving the suitable v
oltage and current on each pin and How should I connect line between PCI-6527 card and 25-pin sub-D plug(I plan to use port 3 of PCI-6527 card).
Thanks, your help is greatly appreciately
zhou

Answer 1

Zhou,
My best recommendation is that you find someone who can give you a better and more direct advise in electronic circuiting. We don't have in our hands the manual of your instrument in order to clarify what it needs and where, although you gave some pin numbers we cannot take the risk of advising something that we don't have the absolute knowledge of. We can give you all the details you want about our card and what does it gives, but you have to decide how are you going to connect it to your instrument. If you recall your email about the manual, in fig. 3-6 page 3-12 you can see a picture of how to connect a TTL driven device, in the last email we gave you an option of how to connect the resistor and where, please read it again, basically I am going to repeat the same, we feel sorry about not been able to give you more help, but is opt to you to find help in electronic theory. Remember in my last email that I told you the 3 cases in which your instrument may need either voltage, current or both, and I told you how RL will change and what new resistors you may need to connect. Review that and make tests with your switch, your question about how to choose the right resistor is answered in the previous email and how to connect lines between the board and the cable of your instrument you have both pin outs... match them... the person who has in his hands the manual and the instrument is the best person to choose how to interfase both appliances... we are sorry Zhou but if we advise you about pin connections of your device with our blindness we have of your device we may make a mistake, we told you about our pins and how to choose resistors.
If you need more direct assistance on this Zhou you may better try to call us, by text messaging is limited and this requires direct guidance. If you decide to call us you can find instructions at www.ni.com/ask hope you move forward in your application as soon as possible.
Nestor Sanchez
Applications Engineer
National Instruments
Nestor
National Instruments