Schematic came up as I was typing - yes, the green wire short circuits the LEDs so they should not / cannot light.

If the green wire is connecting the bottom end of the resistor where it joins to the LEDs to "ground" (negative side of the power supply), it should prevent the LEDs from lighting - it short circuits them. They may have lit with the 10 ohm resistor simply because there is enough resistance in the green wire to allow enough voltage to light them.

Those clip leads are notorious for being high resistance from the start and getting worse as they are used and strands in the wires break, at least in my experience. I used to buy cheap clip leads. With the better quality ones I'd just replace the wire with 22 AWG wire properly soldered to the clips. With the really cheap ones, I'd keep the insulators for the clips and scrap both the clips and the wire.

So is the example in this video impossible LINK ?

 

Without the "GREEN" wire the LEDs light up. As soon as i connect the "GREEN" wire both turn off.

If you short the LEDs, they can't turn on. Doesn't that seem obvious from your schematic?

 

If you short the LEDs, they can't turn on. Doesn't that seem obvious from your schematic?

It's obvious, however from the video on logic gates it appears to work. That brings me to this forum, looking for answers.

 

I think the upper green wire is the positive connection to the meter and the lower one the negative to the meter. The red and black leads are the power supply and the yellow and white are the inputs.

This is what you get with sloppy production by someone who doesn't think about how easy it is to confuse someone who is just starting to learn.

 

I think the upper green wire is the positive connection to the meter and the lower one the negative to the meter. The red and black leads are the power supply and the yellow and white are the inputs.

This is what you get with sloppy production by someone who doesn't think about how easy it is to confuse someone who is just starting to learn.

you are absolutely correct he has the meter connected. . . lol

Thank you,

 

sure here we go:

Without the "GREEN" wire the LEDs light up. As soon as i connect the "GREEN" wire both turn off. (I am using a 200Ω resistor)


View attachment 166020

Modify this circuit like as below. Connect the green wire to either or both of the LED wires. To see the AND gate effect you need to connect the meter as shown.

 

Look at this page...
http://www.play-hookey.com/digital_electronics/dl_gates.html

 

Look at this page...
http://www.play-hookey.com/digital_electronics/dl_gates.html

Thank you BillB,

I understand the logic gates when it comes down to using transistors, but i struggle to understand the logic using diodes in application.
Perhaps some simple rudimentary examples can help. I was able to find a nice video with examples with transistors but not diodes.

 

Try this video..

If you need more, do a search for "diode gate" for several examples

 

Try this video..

If you need more, do a search for "diode gate" for several examples

Thank you Bill B for the video, I have a question:

In the video at 13:28 the professor indicates that the AND gate will be: 0-5-0. Please help me understand, is that a mistake, should't it be 0-5-5?

 

Thank you Bill B for the video, I have a question:

In the video at 13:28 the professor indicates that the AND gate will be: 0-5-0. Please help me understand, is that a mistake, should't it be 0-5-5?

View attachment 166247

Note the connection between A and B. If A=0V and B=5V, there is effectively a short. Thus, point C will be at 0V.

Examine the diagram with all possible combinations of voltages for A and B. You will see how this simple circuit operates.

 

The diagram and table at #30 are simply wrong!

[EDIT]: I hate videos like this so I won't watch it. Does he talk about the diodes as being "ideal" - that is, when a diode conducts current in "forward" mode there is no voltage across the diode? or as "real" silicon diodes where there will be a voltage of around 0.7 V?