Helllllpppp!!! Breadboard

harshudeshpande

What's a Microcontroller
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Page 65: Figure 3-5

I understand why the LED will be off is the push-button is pressed.

What I cannot understand is why is the LED is on when push-button is not pressed. I mean I understand the general concept but I do not understand this specific activity. If the push-button is not pressed then I can trace the current from Vss - resistor - cathode of LED - anode of LED but where is the connection is from anode of LED to Vdd? What am I missing? I tried the circuit, it works.

Thanks in advance

Mike Green

There's a little line from the anode of the LED to Vdd. The dot in this line is a connection. At this point, the anode of the LED is connected to Vdd and to one side of the push-button switch.

In standard schematics, when two lines cross, there's no connection between them unless there's a dot where the lines cross. The dot represents the connection. In this case, the lines just butt up to one other ... they don't quite cross, but the idea is the same. If you just had the "T" where the wire from the switch dead-ends into the wire from the LED anode to Vdd and no dot, that would probably be a mistake in the schematic.

If the switch is not pressed, it's just as if the switch were not there. Try erasing the switch and the lines from it and see what you get. Try again to trace the current.

frank freedman

Careful Mike. That may only apply to ANSI/US standards and practices. In some European drawing standards, specifically German, where a line intercepts another is considered a connection and one crossing over is not a connection. There are no dots. In the drawings released with Siemens X-ray systems, for example, a line representing a video signal path has two components representing connections to the signal. They will stop at the line and will be offset from one another, where in an US originated print they will meet at a common point and have the dot showing connection.

I mention this difference as this forum has a worldwide following and so we need to be careful in our assumptions, especially with new to the art or not familiar with alternate standards and practices in this field.

FF

LoopyByteloose

The problems of a graphic schematic representation of a connection versus a 'un-connected cross-over' has been around since the early days. The old ARRL Handbooks made a precise mention of the fact that their were multiple methods and showed them all.

I fear that since the internet has arrived and self-publishing has become more common - such well-written reference material has slowly been disappearing.

To make matters worse, some schematic software actually doesn't care if the dots are there or not.

These days, European schematics (with boxes for resistors instead of wiggly lines and their own notation) may at times throw a curve into reading schematics. America is still a place that retains some rather quaint graphics. And it is still the only country in the world to refuse to make machinery metric.

In other words, the expert user will always have to be aware of conversion to other systems of measurement. It is a dynastic thing. And other systems of graphic representation to.

Where there is a standard, some is likely to create an alternative standard. We are not quite ready for one world standard. If I want to buy apples in the US - it is pounds; it I want to buy apples in Germany - it is kilos; and if I want to buy apples in Taiwan - it is jin (about half a kilo.)

Mike Green

Thanks for the reminders that there are other standard schematic representations.

harshudeshpande

Please bear with me. I am really new to this stuff. I do not have technical background and it certainly not my age to learn this stuff but I am trying my best to get my son interested.

Coming back to the question:

I do not see any small line from Anode to Vdd. It is neither in the manual nor it is on the physical device. So I am little bit confused as to what you guys are talking about. I also see no lines crossing over each other. I

am pasting a screenshot of the manual here.

What am I missing?

Thanx in advance.

Mike Green

The anode of the LED is the side in the schematic that is triangular in shape. The cathode is the side with a bar.

What may be confusing you in the drawing of the breadboard area is that pins 1 and 4 of the switch are connected together and pins 2 and 3 of the switch are connected together. The switch, as drawn, bridges the two sides of the breadboard connecting Vdd to the anode of the LED. Imagine that pins 1 and 4 of the switch are actually stamped from the same piece of metal. Similarly, pins 2 and 3 are made from another single piece of metal. When you push the button, these two pieces of metal are connected together by a 3rd piece that's attached to the button and is pressed down on the two stamped pieces to make the connection.

harshudeshpande

Aha! you are talking about the schematic drawing. I get that part.

What I do not get is how does it work on the board. The image that I have attached has a physical picture on the right. I do not see the connection from LED to VDD on the physical breadboard. I checked the backside of physical breadboard as well, there is no connection there as well.

Thanx for your patience.

JLocke

See Mike's answer above. The two lower terminals of the switch are connected together (internal to the switch). So the switch is bridging VDD from the left across to the LED on the right. The two upper terminals of the switch are also connected to each other. When you push the button, you connect the top terminals to the bottom terminals.

RDL2004

I remember being a little confused by those switches at first. Maybe this will help. On the bread board, the switch is rotated 90 degrees to the right from the way it's drawn on the schematic.

schill

It sounds like the switch plugged into the breadboard is rotated 90 degrees from the correct orientation.

Switch pins 1 and 4 in your latest breadboard picture are always connected together - completing the circuit and keeping the LED on continuously.

harshudeshpande

"It sounds like the switch plugged into the breadboard is rotated 90 degrees from the correct orientation."

Yes, now I see it

You know why I got confused? There is a discussion in the manual about why the switch must have 4 pins but not 2. If you read the discussion then it will lead you to believe what I was thinking

Thank you everyone. Appreciate your help.