Friday, January 15, 2010
AC Adapter Check
This is just something I thought about doing after observing a voltage greater than 6v with the AC Adapter back in an earlier exercise. It also showed me something that I didn't know about my breadboard (but mentioned in the book, thankfully, or I might have returned my breadboard thinking it faulty).
First, notice in the picture that I'm getting a voltage of zero with the probes even though I'm applying 12 volts. This is because the voltage columns on the top half and bottom half of my breadboard are not one piece from top to bottom. I'll have to cut four small jumper wires to connect them (two for positive voltage side columns and two for negative voltage side columns).
Once I figured that out, it was time to test my AC Adapter. My adapter has a small switch allowing me to select voltages of 3, 4.5, 6, 7.5, 9, and 12. I took voltage readings using two small wires stuck into the breadboard... as you can see from the photo, the actual voltages displayed by the multimeter do not match exactly. For the 6v, 9v, and 12v, the actual readings are almost all .25 higher... one-quarter volt higher than expected. I don't know yet if this will be an issue with later circuits but I imagine it'll involve using higher resistance values if a specific voltage is required... we'll see.
I suggest you do this same thing with your variable AC Adapter... make sure that the voltages you are reading are not too out of range or you may need to return it for a different one. If anyone has any knowledge on the risks of using an AC Adapter that has too much variance in its actual voltage supplied, please let us know.