drive micropump using daq6008

[sapit]

i had developed a fuy logic.vi. The output of this controller will control the speed of the pump which i had connected to the AO1 of the nidaq 6008. However i am unable to drive the pump because the operation of the pump is at 3-12V DC with (50mAmp max). I had tried to use an lm741 op amp with gain equals to 3 but the output voltage dropped when i connect the micropump to the op amp. Pls help me

[johnsold]

The USB-6008 can only produce a few mA on an analog output. The 741 op amp can only source about 10-15 mA.  You need a device which can produce the power needed for your motor.

If the pump does not need to reverse directions, I would use an LM317 adjustable voltage regulator.  Control the Adjust terminal from your USB-6008+741 circuit. You should also include protective diodes.  The LM317 makes a nice, simple, inexpensive, and fairly robust DC motor controller for small motors.  The power source should be at least 15 volts.

Lynn

[sapit]

hi. is the voltage regulator circuit design like this? the protection diode will be added between pin 2 and 3 right? The formula for calculating the value of R2 is V = 1.25(1+(R2/R1)) or to put it another way R2 = R1((V/1.25)-1).

I have a question. Does this voltage regulator varies the output voltge? I need variable output voltage to drive my pump. Should i add another op amp circuit before the voltage regulator?

[johnsold]

Yes.  That is the basic circuit.  The protection diodes are connected as shown here:

To use this as a programmable voltage source you need to make a few changes. The value of R2 is fixed and large enough that it does not load the Analog Output of the DAQ device significantly. R1 connects to ground rather than to Adjust. Its power rating should be 1 W for 12 V operation.  Cadj should be omitted unless the DAQ device can handle the capacitive load. 

The output voltage is the DAQ AO voltage + 1.25 V.

Lynn

[sapit]

thanks. i will try it as soon as possible.