so, I have been trying to understand resistors for years.I watch videos, read books and I keep getting stuck, which in turn makes me give up for a few months...then return and retry with the same outcome.
I understand the math behind Ohms law, but one of the things I do NOT understand is how do I find the relevant information for say...a LDR sensor.
the current arduino book I am reading is "getting started with arduino, 3.rd edition"...and it starts off nice and easy, then suddenly it says to use a 10k resistor for a LDR sensor withouth any further explanation as to why, how can I gain the information needed to do the calculations that says I need a 10k resistor for the sensor?
if ANY of you masters out there are writing a beginners arduino book....here's a suggestion:
for the first few chapters, explain WHERE to get the information required and how to do the calculations instead of going:
"and for this chapter we'll use a huge motor and throw a 0.00001 resistor on it, it will power a fan, a house and a car so that's all we need....but wait there is more, we also have this Led...so you need to connect a 10k resistor to that...ok, next chapter"
in all books/videos I have come across, there is a huge gap that needs to be bridged between explaining Ohms Law
then going "use a x resistor for this circuit" where it is assumed the reader/viewer knows how to get the required information, and what information they are looking for.
You are making a [u]Voltage Divider[/u]. i.e. When both resistors are equal the voltage is divided evenly and you get half of the applied voltage a the center point (referenced to ground). Otherwise, the highest resistance gets the most voltage "dropped" across it.
A pot (potentiometer) is also variable voltage divider.
You can figure that out yourself using Ohm's Law as long as you know a couple more things: Resistances adds-up in series (two 10K resistors make 20K), and that the current is the same through series resistors. That's easy to understand if you understand that current "flows".
The way voltage & current combine in series and parallel are Kirchhoff's Laws
if ANY of you masters out there are writing a beginners arduino book....here's a suggestion:
I'm not an author but this situation is this: There is a lot to electronics and if you were studying electronics in college you wouldn't be learning about microcontrollers until the 3rd or 4th year! You'd also be taking a few programming classes and 4 years of advanced math.
The good news is, digital electronics is easier than analog and Arduino programming is a lot easier than writing a Windows (GUI) program.
DVDdoug:
You are making a [u]Voltage Divider[/u]. i.e. When both resistors are equal the voltage is divided evenly and you get half of the applied voltage a the center point (referenced to ground). Otherwise, the highest resistance gets the most voltage "dropped" across it.
A pot (potentiometer) is also variable voltage divider.
You can figure that out yourself using Ohm's Law as long as you know a couple more things: Resistances adds-up in series (two 10K resistors make 20K), and that the current is the same through series resistors. That's easy to understand if you understand that current "flows".
The way voltage & current combine in series and parallel are Kirchhoff's Laws
I'm not an author but this situation is this: There is a lot to electronics and if you were studying electronics in college you wouldn't be learning about microcontrollers until the 3rd or 4th year! You'd also be taking a few programming classes and 4 years of advanced math.
The good news is, digital electronics is easier than analog and Arduino programming is a lot easier than writing a Windows (GUI) program.
this too...doesnt explain what I am asking....I have a tutorial,tutorial says LDR sensor + 10k resistor.
you know just as much as I do at this point.....please explain the logic why I should understand that the LDR sensor NEEDS a 10k resistor, instead of say...a 330.....you have just as much information as I do.
It may sound simple but you must learn to crawl before you run.
You must know some math before you can understand what a voltage divider does.
If an LDR has a dark resistance of 10k and a resistor in series with the LDR is also 10k then it should (hopefully) be obvious there will be the same voltage dropped across both elements when current flows.
Sounds like you skipped over the first few chapters in your math and electronics books.
Go back and start slowly and learn the very basics.
Before you choose a resistor you must determine what your goal is.
taking your LDR example my guess is you would like an arduino to output some numbers that represent Light falling on the LDR.
Looking at the LDR graph (obviously you find that by googling LDR)
Then you must make a decision, What is the range of light your interested in? Lets assume you wish to measure from bright sunlight (LDR = 20 ohms) to somewhere below lighter room (LDR = 10K)
So now you have to know the specifications of your arduino. Vin = ?? (5V or 3.3V).
The only way I know an arduino can measure a varying signal is via the Analog Inputs. So go to the arduino spec and see what inputs the analog inputs requires.
Let me know if this is what you seek......
Remember there is no Quick answer you will find electronic design is very detailed.
larryd:
It may sound simple but you must learn to crawl before you run.
You must know some math before you can understand what a voltage divider does.
If an LDR has a dark resistance of 10k and a resistor in series with the LDR is also 10k then it should (hopefully) be obvious there will be the same voltage dropped across both elements when current flows.
Sounds like you skipped over the first few chapters in your math and electronics books.
Go back and start slowly and learn the very basics.
"If an LDR has a dark resistance of 10k "
how would I know what "dark resistance" it has? where do I find this type of information?
in ALL tutorials both books and videos it is just assumed the beginner somehow magicly know this information
Hakaari:
I have come to the conclusion that I won't be able to understand this aspect. and will no longer try to pursue a hobby within electronics.
thank you for your replies that had nothing to do with the issue at hand.
That is unfortunate. I also think it is short-sighted. But, you know yourself better than we do.
If you have no curiosity, than no, electronics is not a good choice. But, if you want to understand how electrical things work and you understand knowledge is built incrementally, in small bites at time, it’s a great field of study.
It’s a process. One step at a time. These days, the world is available to you with a click of a mouse. All knowledge is interconnected. Start somewhere. Just pick a topic.
You could start by learning about two fixed resistors, as mentioned. That’s a voltage divider. Then, changing one resistor to be adjustable and you have the circuit you’re asking about. An LDR is a resistor that changes its value based on the amount of light it is exposed to. In order to measure that resistance, you need to force a current through the LDR which will result in a voltage across it that changes with light level.
The graph shown in post #3 shows the relationship between light level, shown in the horizontal direction (x axis), and it’s resistance in the vertical direction (y axis).
One last thought - it’s not a surprise you’ve found this thread to be frustrating. You were directed to find the “dark resistance” of your LDR. The graph shown does not show that value in a direct way. You would need to research, which takes about ten seconds with Google, that 10 lux is the same a twilight night. So, I’d call that the dark resistance. It’s about 7000 ohms or 7K.
Well, no, for a particular sort of LDR you have - which may be a very common sort - it may well be about 7k Ohms (where "7k" is a standard prefixed shorthand for 7 x 1000). But not for every LDR. And "7K" is not meaningful.
if ANY of you masters out there are writing a beginners arduino book....here's a suggestion:
for the first few chapters, explain WHERE to get the information required and how to do the calculations instead of going:
My guess the OP is not willing to do any investigation on their own, wanting to have information handed to them.
I have come to the conclusion that I won't be able to understand this aspect. and will no longer try to pursue a hobby within electronics.
thank you for your replies that had nothing to do with the issue at hand."
I have come to the conclusion that I won't be able to understand this aspect. and will no longer try to pursue a hobby within electronics.
thank you for your replies that had nothing to do with the issue at hand.
" the issue at hand."
how can I gain the information needed to do the calculations that says I need a 10k resistor for the sensor?
If the LDR has a 10k dark resistance 2 10 lux then you wouldn't use a 10k resistor for a voltage divider because
then the voltage would only be divided in half if there was no light.
You need to look at the graph in Reply # 2 and note the resistance at some higher light level , light between
100 and 1000 lux and you will see that corresponds to a resistance between 100 ohms and 1000 ohms, so
if , for example you picked a light level in the middle of the "well lighted room " range then the LDR resistance
would be 500 ohms.
Given a voltage divider where R2 = 500 ohms and Vcc = 5V, you can pick the desired output voltage of the voltage divider and solve for R1, using the standard voltage divider formula.
If that's too much work then maybe electronics isn't for you...
Hakaari:
how would I know what "dark resistance" it has? where do I find this type of information?
You get this information from the datasheet. If you are doing any kind of design work on your own, you must have the relevant datasheets. Otherwise you are fumbling in the dark, as you have been. We are now in a golden age for experimenters: hundreds of thousands of electronic datasheets are available at your fingertips. Google will find them. Once upon a time, you needed a whole shelf of books, which was far less comprehensive and also subject to obsolescence.
S.
I still have my shelf of data books and text books from long before the Internet and forums like this. Some are tattered and dog eared from long usage. Can't make myself throw them away even though they are useless.
groundFungus:
I still have my shelf of data books and text books from long before the Internet and forums like this. Some are tattered and dog eared from long usage. Can't make myself throw them away even though they are useless.
I know what you mean. For those of us outside of the industry, they were sometimes difficult to obtain in the first place ... and treasured as a result.
S.
Seems to me that OP doesn't care to read given instructions. Sounds like my ex-wife, today I tried
to help her to connect PC to bluetooth speaker. After 10 minutes I told her to connect it with cable,
but even that wasn't easy enough, she couldn't understand what 3,5mm plug is...
You say you spent years trying to understand resistors? Try ohms law first, you must know that
there's more than just the resistance playing this game?
Do you have a digital multimeter? You should. Connect your LDR and read the measurement
on the complete dark place, little light and finally on the day light. What can you tell us about
the resistance?
