myDAQ voltage measurement through analog input

[drmegu]

Hi all,

I am a beginner to the myDAQ interface and electronics and trying to build circuits to see the performance of my 5V converters with various capacitors. I built the little converter setup below without any capacitors to check and record how the V increase while its turned on.

It simply uses the 15V voltage from myDAQ ports and converts it to 5V when the button is pressed. I checked it using the multimeter probes and with an another external multimeter and it seems working fine.

I wanted to record how it switches on/off and used "test panel" feature at NI-MAX to see how it is doing during increase and decreases before writing a VI. Although I measure 5V using multimeters, this interface measures about -2V while the button is not pressed and when it is pressed it inceases to about 2.45 V. Please see below:

I thought if this is because it is measuring in a differential setting but it cannot be changed. ~-2 - 2.45 V interval also makes only 4.5 V where half a volt is missing. So it did not make sense since the multimeters are measuring 4.99 or 5.00 V precisely.

Can somebody please tell me what is going on and the reason behind this? Can you also please guide how I can make it correctly?

Cheers,

Matt

[santo_13]

You've connected the GND of output to DGND, you've to connect it to AGND near the AI0+ and since you've connected only the AI0+ you've to configure the test panel to use "single ended RSE" instead of "Differential"