generate DC volate and aqure voltage signal with PCI6221

[amaka]

Hi ,

I am quite new to LabVIEW. I am trying to supply two voltages to two LED’s and take one detector voltage in. I am using SCB-68 board connected to PCI6221 DAQ card and LabVIEW 8.2. Is it possible to supply and acquire voltages as I explained without any other external devices?

[titi_nicolas]

Yes you have everything you need

PC - PCI dac card <---> cable <---> SCB board ----> your circuit!

[AnalogKid2DigitalMan]

What will be supplying voltages to the LED's?

Analog outputs are limited to 5mA (probably inadequate)

Digital outputs are limited to 16/24mA (probably sufficient but the voltage levels are fixed).

You may need some type of current amplifier if you need to supply more current to the LED's using the analog outputs.

What range of voltage does the detector put out?

[amaka]

Thanks for the instructions.

It seems I need to have a power amplifier to drive my LED’s since they need at least 30mA. Does anyone know whether I can find such a amplifier in the market.

Thanks.

The detector output going to be very less. Probably less than 1V.  I think this does not make any problem to the DAQ.

[titi_nicolas]

What is your experiment?  Depending on what you want to do, your circuit can be more or less complex.

Do you need to drive the LED in DC or AC (then at which frequency)?

Even if the DAC card can mesure signals in the mV range, there is still noise in the environement! I don't know how sensitive and accurate you want your measurement to be. But if you want something with a low noise level you should consider amplifying (and also filtering for better result) the signal coming from the detector.

[amaka]

I am planning to read two LED output with the detector so that LED output can be controlled with the signal coming out from the detector.  LED’s are powered by DC current. I am trying to do this without using a precision current driver ( I want to keep the system very simple) , so I need to amplify ~5mA DAQ current output to around 50mA. Now I am trying to find kind of current amplifier suitable for this.

[titi_nicolas]

a cheap and fast solution to drive your LED is to make a circuit with an Op Amp in the "voltage to current" configuration.

You will also need a DC power supply for the Op Amp.

Look at this link for basic explaination: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar2.html

or this one http://eportal.apexmicrotech.com/mainsite/pdf/an13u.pdf

The design can be improved by adding a transistor a the OpAmp output.

see this :http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

Message Edited by titi_nicolas on 05-25-2007 11:03 AM