running a 5V relay via a BNC-2110?

[NeuralJ]

Hi,

     is it possible to run a 5V relay via a BNC-2110? I have the NI card installed in my PC, and the BNC-2110 is hooked up to the PC. Th BNC-2110 is run by a neuroscience program, and I need to be able to control a 12V regulator once the 5V relay is switched on by the program.

Any help will be greatly appreciated.

[Dennis_Knutson]

You can't 'run' anything with a 2110. The BNC-2110 is just a terminal block and has no digital I/O or other electronics on it. If you are connecting the BNC-2110 to an NI DAQ board that does have digital I/O, then you might. You need to determine the actual DAQ board being used and look up the current output for the digital signals. Then, see what the relay requires. I generally use a relay driver ic between the digital I/O board and a relay to provide enough current and some isolation.

[NeuralJ]

Thank, Dennis.

The NI DAQ card we are using is the 6025E.I know it has a analog output of +/10 V, but I'm not sure of it digital ouput. What type of wires would I need to get it connected to the Digital and Timing I/O blocks?

[Dennis_Knutson]

You've got 32 digital I/O on that board. It doesn't really matter that much what type of wire if you are doing some static digital. Something like 26AWG should work fine. The other connectors would be used for analog inputs or outputs. They are for connecting coax cables. You've only got 2 analog outputs so you could use those if that's enough.

[NeuralJ]

Dennis,

How can I specify which port from the Ni-DAQ card should output the 5V to the BNC-2110? Would I use the screw terminals? It's my understanding that the relay needs leads  coming from the BNC-2110 so that it can be powered.

Thanks.

-- J

[Dennis_Knutson]

Do you have the manual for the BNC-2110? If not, you can download it from here. It looks like the screw terminals labeled P0 through P7 correspond to digital I/O port 0 bits 0 through 7. With DAQmx, you can select an entire port or line and use DAQmx to drive it high or low. There are shipping examples that show how to do this. The DAQ Assistant can also be used. Your comment aabout powering a relay is different than controlling the relay's state. A relay will need a power connection and a logic connection to open/close it. You'll also want to look up the manual for the DAQ board to see what kind of current it can source and you'll need to know the relay's specs to see if the DAQ board will work by itself.

[NeuralJ]

I have a third-party software that can control the state of the relay. I thought that Ni- DAQ 6025E could provide power to the relay once connected to the BNC-2110?

You also mentioned DAQmx and DAQ assistant. Can you tell me what they are and where to access these?

Thank you.

[Dennis_Knutson]

Using an expensive DAQ board to just provide 5VDC seems a little silly. You could buy a cheap wall transformer from radio shack for around $10. If you wanted, you could also build an extension cable from one of the internal power plugs inside your pc.

If you are not going to control the relay with digital lines from the daq board, you don't need DAQmx or the DAQ Assistant. Nor do you need either if you just provide 5 volts from the DAQ board. The DAQ board has a fixed 5 volt output pin. If you do want to experiment with controlling the DAQ board, then go to the NI Measurements>DAQmx palette. If it's not there, then DAQmx might not be installed. See if you have a Data Acquisition palette under NI Measurements. The functions there use an older DAQ driver.

[NeuralJ]

Thanks, Dennis.

See, the first attempt at buidling this circuit was just using a 5V mini relay from radio shack. The set up was constructed so that the 3rd party software would interface with the relay via the parallel port of the computer. However, the parallel port had a maximum voltage output of 5V, so we could never have enough power from the parallel port to power our relay. Since there's no vendor that I can find that sells a 3 V relay, I was told by the software programmer to skip the parallel port by using the NI DAQ and BNC -2110.  He set up the hardware and software so that the NI DAQ card and software interface to control the relay state and the BNC 2110/Ni DAQ could provide the 5V to power this circuit.

I've also been told to look into photcouplers and transistor circuits. Being a newbie to this type of science, it seemed that the relay was the easiest set up to go with. When that failed, the NI equipment looked to be the next best option.

[Dennis_Knutson]

The problem with the parallel port's 5 volts is probably that it can't provide enough current and the fixed 5 volt output on the DAQ board is not a high current source either. As I said earlier, you can look up this information in the manual for the DAQ board. There should be some specs provided for the relay. If nothing else, it should provide the coil resistance. Using Ohm's law, you can calculate the current. V=IR or I=V/R where V=volts(5), R=resistance, and I = current. If the I you calculate is greater than the spec for the NI board, you can't use the board.

I'm sure you can find an inexpensive wall transformer. I'm sure you've seen these. They are those little black bricks you plug into a wall socket to do things like charge your cell phone, iPod, etc. They will have a marking on them that state the DC output voltage and current. Find one that provides 5 volts and enough current.

This is starting to sound like some school project. If the task is to design a 5 volt power supply, then maybe you should be looking into transformers and voltage regulators.