Return to Answer

Can't get consistent readings from Sharp IR range detector

Where to put stabilising capacitor?

Daisy chain (parallel) of IR sensors

Sharp Infrared sensor-Filtering supply ripple

Where to place a capacitor to smoothen IR sensor reading?

How do I properly use Sharp GP2Y0A21YK0F sensor?

Can't get consistent readings from Sharp IR range detector

Sharp IR distance sensor outputting consistently high voltage

Can't get consistent readings from Sharp IR range detector

Where to put stabilising capacitor?

Daisy chain (parallel) of IR sensors

Sharp Infrared sensor-Filtering supply ripple

Where to place a capacitor to smoothen IR sensor reading?

How do I properly use Sharp GP2Y0A21YK0F sensor?

Can't get consistent readings from Sharp IR range detector

Sharp IR distance sensor outputting consistently high voltage

You have fallen into a classic XY problem trap. You have a genuine problem:

That is not enough detail to help you with the actual problem, but I'll come back to that. You chose an (unfortunately inappropriate) test, and are now having problems interpreting the results. Unfortunately you don't realise that this is the wrong issue on which to be spending your time, as the result won't help you with the original problem:

Unless you have evidence that there is a short-circuit (which often won't be the case, if you just guessing at what troubleshooting to do), then using a typical multimeter in that way on a board with ICs installed, will lead to lots of false positive apparent shorts displayed on the meter. This is due to the ESD protection diodes (and other ESD protection structures) inside the ICs, which may conduct during that "continuity" testing.

Sharp IR distance sensor outputting consistently high voltage

You have fallen into a classic XY problem¹ trap. However, thanks for briefly mentioning the original issue, as that makes the overall situation easier to understand. 

You have a genuine problem ("X"):

That is not enough detail to help you with the actual problem, but I'll come back to that. You are having problems interpreting the results from an (unfortunately inappropriate) multimeter test, and that is what you were asking about ("Y").

However "Y" is the wrong issue on which to be spending your time, because getting an answer to that, won't help you with solving the original problem "X". As confirmation, below is the answer to your question "Y" (about the apparent shorts you measured) but it doesn't help resolve the real problem "X" (about the sensors, when powered by the DE0-Nano):

Using a typical multimeter in that way on a board with ICs, will usually lead to lots of false positive apparent shorts displayed on the meter. This is due to the ESD protection diodes (and other ESD protection structures) inside most ICs, which can conduct during that "continuity" testing.

Sharp IR distance sensor outputting consistently high voltage

¹ There are several slightly different definitions of the XY problem so I linked to a Google search above, for readers who want to learn more. The terminology I use is:

"X [is] the underlying problem and Y the exposed question or request"

which is adapted from here.

• Go back to your earlier configuration which you say worked i.e. external separate power supply for the 3.3V and 5V sections. I hope (and suspect) this will work again. This would confirm your hardware has no "short circuits".

• Note that some Sharp distance sensors have unusual power requirements. Specifically they pulse their IR LEDs at relatively high currents, for brief periods. Due to those high currents, they are well-known for needing lots of decoupling capacitance close to the sensors, especially if the power supply is weak, or has lots of inductance (e.g. long / thin wires etc.). Your sensor's datasheet mentions average supply current (12mA to 22mA) but not a maximum current!

• Go back to your earlier configuration which you say worked i.e. external separate power supply for the 3.3V and 5V sections. I hope (and expect) this will work again. This would confirm your hardware has no "short circuits".

I suspect that either additional output capacitance and/or a higher current capability of that separate DC power supply (compared to the DE0-Nano's power output), is why that configuration worked - see next point.

• Note that some Sharp distance sensors have unusual power requirements. Specifically they pulse their IR LEDs at relatively high currents, for brief periods. Due to those high currents, they are well-known for needing lots of decoupling capacitance close to the sensors, especially if the power supply is weak, or has lots of inductance (e.g. long / thin wires etc.). Your sensor's datasheet mentions average supply current (12mA to 22mA) but not a maximum current!