What is a Microcontroller? - Questions from a 9th grader, Thanks
mj37
Posts: 6
I am 9th grader and I am going thro the book (What’s a Microcontroller?) and following the activities on my own. Although I don’t understand lot of things in the book, it is fun to build·circuits and make them to work. I can’t wait to finish this book and·build boe-bot.
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In some occasions, I am blindly following instruction without understanding. This is a good book and really like it. I am in·chapter 5 now. I think the book requires some knowledge in electricity (physics), or help from a teacher.· Some of my questions are below. Thanks for your help.
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1)····· I understand the current flow is typically shown in the wrong direction (page 45). ·Do I have to always assume the opposite when I want to visualize the flow?
2)····· I am especially confused by the LED symbol and current flow. Any help?
3)····· I also seem to understand that resisters are used to limit the current flow that can damage the circuit (page 48). Does it matter where to place before or after an LED?
4)····· When a bicolor LED is used, we reverse the current flow. In this case, don’t we need to have two resisters? (pages 62, 63)
5)····· I have reached chapter 4 successfully. The servo motor control program (page 115) made sense. But when I ran the program, the motor spins completely several times before it finds 10 0’clcok, makes several spins before it finds 2 o’clock, and again spins before it found the 12 o’clock position. How does this work? Can the motors find all these position in one rotation?
6)····· Also, how do I know where these positions are?
I am writing down my questions as I do the exercises and if it is ok, I want to ask·for some help like this. Let me know if this forum is not for simple questions.
·melissa
·
In some occasions, I am blindly following instruction without understanding. This is a good book and really like it. I am in·chapter 5 now. I think the book requires some knowledge in electricity (physics), or help from a teacher.· Some of my questions are below. Thanks for your help.
·
1)····· I understand the current flow is typically shown in the wrong direction (page 45). ·Do I have to always assume the opposite when I want to visualize the flow?
2)····· I am especially confused by the LED symbol and current flow. Any help?
3)····· I also seem to understand that resisters are used to limit the current flow that can damage the circuit (page 48). Does it matter where to place before or after an LED?
4)····· When a bicolor LED is used, we reverse the current flow. In this case, don’t we need to have two resisters? (pages 62, 63)
5)····· I have reached chapter 4 successfully. The servo motor control program (page 115) made sense. But when I ran the program, the motor spins completely several times before it finds 10 0’clcok, makes several spins before it finds 2 o’clock, and again spins before it found the 12 o’clock position. How does this work? Can the motors find all these position in one rotation?
6)····· Also, how do I know where these positions are?
I am writing down my questions as I do the exercises and if it is ok, I want to ask·for some help like this. Let me know if this forum is not for simple questions.
·melissa
Comments
If these are all the questions you have, you are doing great [noparse]:)[/noparse]
1) I understand the current flow is typically shown in the wrong direction (page 45). Do I have to always assume the opposite when I want to visualize the flow?
I teach at a university, and we can order text books that shows flow using either direction. Electrons flow one direction, the holes they leave appear to flow in the other direction. It really doesn't matter which way the flow is shown, as long as you understand some other people may go the other way. What is important is that some devices allow flow in only one direction (diodes) and that the amount of current flowing is very important.
2) I am especially confused by the LED symbol and current flow. Any help?
An LED is a Light-Emitting Diode. A diode only allows flow to travel in one direction (with the arrow using conventional flow). The material the diode is made of emits light when electrons flow through it. So it's important to always connect an LED in the correct direction to ensure current will flow and it will light.
3) I also seem to understand that resisters are used to limit the current flow that can damage the circuit (page 48). Does it matter where to place before or after an LED?
Nope. When we look a the LED and resistor, they make what's known as a series circuit. Current flow will be the same no matter the order. Think about current like water flow. If you have a hose and pinch it at the far end, only a certain amount of water can flow from the facet and out the end. The faucet can't put more water into the hose than can come out once full (or it would expand like a ballon). Current in a series circuit is the same. No more can be pushed into it than is coming out the other end. So which goes first or last doesn't matter in these circuits.
4) When a bicolor LED is used, we reverse the current flow. In this case, don’t we need to have two resisters? (pages 62, 63)
Same as above. Current can flow in both directions through it (unlike a normal single LED), but in both cases the resistor is in series or in line with the current flow and preventing an excessive amount.
5) I have reached chapter 4 successfully. The servo motor control program (page 115) made sense. But when I ran the program, the motor spins completely several times before it finds 10 0’clcok, makes several spins before it finds 2 o’clock, and again spins before it found the 12 o’clock position. How does this work? Can the motors find all these position in one rotation?
Does it spin completely around (360?) When you turn it by hand, are there mechanical stops or does it spin and spin? It sounds like you might have a continuous rotation instead of a standard servo which can only turn a certain amount. Let us know more about what you find, read the name plate on the front and tell us.
6) Also, how do I know where these positions are?
See #5.
You're doing great! Keep posting if my answers don't satisfy you, or you have more!
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Welcome to the world of Stamps and Robotics, its always great to see young females interested in the field. Martin did a great job explaining your answers, so I won't re-explain them·and I too frequently rely upon describing water flowing as an analogy for electricity when explaining things to someone that doesn't already understand, many different aspects of electricity can be explained using water flow as an example.
To give you a background on the current flow confusion, Benjamin Franklin himself when he was doing experiments in electricity noticed current flowing and the positive and negative poles of batteries. Since he didn't understand the physics or chemistry underlying the behavior he was seeing, he basically arbitrarily defined current to be flowing from the positive terminal to the negative terminal. And it became defined as such, even when it was later disproven (that the reverse was the case) it had already been established so people continued to define it the way he did, even though we now know better.
The symbol for a diode is a triangle pointing into a bar (figure 2.4 of What's a Microcontroller, symbol underneath the picture of the LED), for the LED to light up it should be oriented so that the triangle points in direction of current flow as Franklin defined it, another way to remember is the bar is on the negative side (negative sign looking part on negative side of power). When looking at an LED you'll see a flat part to it, you can think of this being the bar in the symbol, so the wire nearest the flat part is the negative wire.
Good luck, and don't be afraid to ask questions, we'll be happy to answer them.
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·1+1=10
Post Edited (Paul Baker) : 12/13/2005 4:27:44 PM GMT
If it makes spines then it means that it is a continious rotation servo. Not a simple one...
This means that the inner pot of the servo is centered·or·just not to move (when it is a continious rotation one)·when we sent a "750" centering pulse!!!
I know almost all the programms figured in WAM, bacause that's how I started!!! (Parallax, thanks)
You must have a FOR...NEXT flow diagram, right?
Please upload the code...
There are many things you can do with a non-continious servo!!!!!!!
Provas, GReece
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See Kirchoff's Current Law and Kirchoff's Voltage Law for more formal answers to some of your questions (1, 3, maybe 4). KCL covers why it doesn't matter which side of the LED the resistor is on. You can also use these, along with Ohm's Law, to derive the formulas for series and parallel resistor values.
KCL: http://www.regentsprep.org/Regents/physics/phys03/bkirchof1/default.htm
KVL: http://www.regentsprep.org/Regents/physics/phys03/bkirchof2/default.htm
These are the simplest explanations I could find. Most of the others either explain it from a physics point of view (conservation of charge and conservation of energy), or present it at a college level. Google for "Kirchoff's Law" if you want to see what's out there.
A high school physics (electricity & magnetism, not mechanics) text might also have a good explanation (although high schools seem to use college texts in any case).
Mike
I hope to complete the wam during the break and start the boe-bot. One thing I have realized is that I am using the boe-bot kit with microcontroller text. The servos that come with boe-bot kit are continuous. That probably explains the problem I have with the activity on page 115. The motor that I have can spin completely. Does this mean I can’t complete the exercises in chapter 5 of wam? Or should I buy a different servo motor?
Thank you all again
Melissa
You probably mean endlessly... Well then you probably have to buy a new servo...
An RC aircraft servo... Once you have bought it run again the programme... It sould be cool...
And you don't have to call me Mr.!!!
Respectively, Provas, GReece.
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-Rule your Destiny-
--Be Good. Be Bad. Be Provas--