Friends,

I'm working on a project to build a marble auger for my son. I've got my protoboard all wired up and tested, and the code is verified to work okay. But when I plugged it into the 5VDC power supply I had bought for the purpose, nothing happened. A surprising result! What is going on!?

I took out my voltmeter and measured a few voltages and found that the voltage coming from the DC jack was the opposite of what I expected. Here's the data sheet:

https://www.cui.com/product/resource/swi10b-n.pdf

And a picture of the jack I have:



By my read of the datasheet and the jack, this should be a center-positive barrel connector at 5v. Is that right?

So, after measuring the negative voltage, I unplugged the connector (thank goodness for my protection diode to the MCU!) and I tested the jack with my multimeter. I have my multimeter set up as pictured here:



I placed the black tip of the multimeter in the center of the barrel jack and the red tip along the outside. In this configuration, the multimeter measured -5 V.

By way of demonstrating that I'm not imagining things, here is a video of the same:

https://photos.app.goo.gl/2eEbVrAPQJ4gKt5f7

This is really surprising to me! Am I using the multimeter wrong, or have I misunderstood what the part is supposed to do, or is the part not doing what it says on the tin?

Thanks in advance for entertaining this extremely newbie question.

 

Never mind, I'm a silly person. The red of the multimeter is supposed to go on the + terminal. So the voltage is correct, and my bug is elsewhere.

 

Some strange American thing having AC hot is black, so I suppose that leads to confusion when new to measurements and multimeters.
Anywhere else, hot is anything other than black or green.

 

Hah. Boostbuck, that is very kind of you to assume it was anything other than a very dumb mistake. Which is what it actually was.

In case anyone ever wonders what my actual mistake was that made my part not work when I first plugged it in: I initially measured the barrel plug and saw that both wings were continuous. I assumed that meant they were the same. But in fact, one of the wings is a switch that is connected to ground when there is no plug but otherwise is disconnected. That was the wing I had grounded everything to. Doh!

Now the whole assembly works as expected. I'm a happy camper.