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ADALM2000: Activity: Diode I vs. V curves, For ADALM2000

Hi,

I just started using the ADALM2000, this is the first exercise that I am trying to do from the "Electronic i" section, I have linked the activity below

https://wiki.analog.com/university/courses/electronics/electronics-lab-2?force_rev=1

In this activity section I am trying to study the I vs V characteristics of the 1N914 diode. The lab directs to use the differential input of the channel 2 (2+, 2-) to measure the voltage across the resistor which divided by the resistor value gives current through the resistor and diode, however I end up measuring only the input voltage and when I connect the "2-" terminal of the channel 2's probe to the lower leg of the resistor it basically seems like shorts the diode (as the other probe is measuring the voltage across the diode) and I end up with only input waveform on the scopy. Am I missing something here? is there a setting that needs to be enabled on channel 2 to turn it into a differential probe?

My understanding is that the "2-" terminal and the "1-" terminal are internally grounded and so that is why when the "2-" terminal is connected to the lower leg of the resistor it shorts the diode out.

Thanks

Bhavani

  • Are you sure you have everything connected exactly as shown in figure1? You should have 6 wires connecting the M2k to your breadboard. Double check your wiring, if correct scope channel 1 should display the voltage across the diode and channel 2 should display the voltage across the resistor. With 1- still connected to GND move 1+ to W1. It should now display the W1 waveform and it should match what you set it to in the signal generator. Likewise if you leave 2+ connected to W1 and move 2- to GND you should see the same waveform you have set the signal generator to.

    To answer: "My understanding is that the "2-" terminal and the "1-" terminal are internally grounded". There are two 1 Meg Ohm voltage dividers connected to the + and - inputs of the scope channels (total of four resistor dividers). The inputs 1+, 1- and 2+, 2- connect to the "top" (input side) of the resistor dividers. The "bottom" of the resistor divider is grounded. The divider taps (output side) are connected to the differential inputs of the amplifiers that drive the two 12 bit ADCs.

  • Hi  ,

    Thank you for the reply, I have attached the two setups and their respective outputs.

    Setup1: Channel1 in orange, connected to the top leg of the resistor giving the input triangular waveform 6Vp-p in orange.

    Channel 2 in blue connected across the diode which give the output where the output voltage is clipped off above 0.6V as expected.

    Stup2: "2-" ( black GND lead of  Channel 1) connected to the lower leg of the resistor and the output on channel 2 drops completely.

    I hope the pictures help, please let me know if you need more details. I have thoroughly checked the connections and everything seems correct, I have not looked into the schematics of the ADALM2000, but I did a quick continuity check of the 2- and 1- probe leads and they seem to be shorted and that also explains what I am seeing the output of 2nd setup.

    I am using the BNC adapter board is that what is causing this as the schematic of this board shows clearly both the BNC probe's GND leads being shorted 

    Fixed the issue, removed the BNC adapter board and everything is working as given by the activity page.

    Thank you for the help.

  • Solution: Don't use the BNC adapter boards for some, preferably all, of the activities of Electronic-i and ii activities.

  • You didn't mention you were using the BNC adapter. If you read the documentation on the BNC adapter, by default the negative inputs 1- and 2- are grounded through solder jumpers on the PCB. Thus the inputs are single ended. Also as documented in the page on the BNC adapter is how to change the solder jumpers to use the AWG BNC connectors for the negative inputs allowing access to the differential scope inputs at the expense of one or both of the AWG output BNCs.

    wiki.analog.com/.../bnc

    You are correct that any of the activities on the ADI Wiki that use the floating differential inputs can only be done with the fly wire harness. But that is not all of the activities, very few actually require use if the floating differential input functionality.