Hi guys,
I have a short question about the analog inputs of the arduino. I have the following situation:
How can I detect the voltages of the divider? So I'm higher then the accepted 5V and I have the condition that no further resistors will used in the A0-line.
Do you have any idea, how to detect a signal higher than 5V. When I use further resistors, I will manipulate the signal...
Would be nice, if somebody has an idea 
big thanks
homerunjack
DETECT? You don't need to detect. If you simply calculate the value of your resistors then it WON'T go over 5v.
If you're not certain of your input voltage, you could always include a zenner diode in parallel with the lower resistor.
No, I have to detect. The point is, the resistor R2 (on GND side) is changing during the process, because on this side, some other resistance will be switched on, so the total Resistor R2 will change his value. Both R1 and R2 are fixed...espacially R2 is changing, but have the fixed 100 or 50 or 10 value.
So I have to detect the voltage over R2 without an additional divider, because the signal has to be "untouched"...
In dependence of the second resistor, the voltage has to be detected and the voltage at the measurement point has to be 12V, 8V or 2.2V...
Is there any ADC where I can factorize the signal? For example 12V --> ADC *0.2 --> 2,4V at A0?
100 ohms is way too small a value for a resistive divider here - the power dissipation
is very large, several watts.
Choose a lower resistance of about 10k and select the upper value appropriate to
the voltage range of interest. For a range of upto 12V use 15k upper resistance, 10k
lower resistance, this will scale 12V to 4.8V.
You can't feed that signal straight into A0 of an arduino. You'll kill it. You could always add another divider with much bigger (say 3.3k and 4.7k) values in parallel with that bottom resistor.
Even if you totally ignore the imbalance this makes to your first divider, your results should still e within 1%
KenF:
You can't feed that signal straight into A0 of an arduino. You'll kill it. You could always add another divider with much bigger (say 3.3k and 4.7k) values in parallel with that bottom resistor.Even if you totally ignore the imbalance this makes to your first divider, your results should still e within 1%
It's clear that I cannot bring the 12V into an input. My problem is, that the resistors are fixed. I cannot change them. The second resistor (at GND side) will change, (because other resistors will switched parallel, so the 100, 50, 10 Ohms are the total R of the both parallels...).
These Values are only symbolic values. The problem is to find out the voltage at this place, without modify the signal. When I try to get a second divider parallel to R2 the total R2 will change and I will lose my 12, 8 and 2.2V ...
I think the idea with the second, extremly high resistance divider is an option...
I guessed that there is any device, that can scale down the signal...
Yes, use a second resistance divider of much higher resistance. And if the voltage on the divider goes above 12V, and therefore the input to the Arduino goes above 5V, the greater resistance will ensure current through the Arduino's protection diodes is low enough not to damage them.
The Arduino (actually, the AVR microcontroller) should have an impedance of no more than 10k for fastest, most accurate analog reads. So the thevenin resistance of the added-on divider should be 10k or less.
You don't need to get 12V scaled exactly to 5V, just to something 5V or less, but close to it. The higher the resistance the better, more protection for the Arduino from overvoltages.
That's 7V drop and 5V drop, the closest standard values in that ratio that spring to mind:
6.8k and 4.7k ... way below 10k thevenin resistance, we can go higher
15k and 10k ... 6k thevenin resistance, and 4.8V out for 12V in
18k and 12k ... 7.2k thevenin resistance, and 4.8V out for 12V in
22k and 15k ... 8.9k thevenin resistance, and 4.865V out for 12V in
27k and 18k ... 10.8k thevenin resistance, and 4.8V out for 12V in
KenF:
Even if you totally ignore the imbalance this makes to your first divider, your results should still e within 1%
It's also calculable so it shouldn't be a problem.
It sounds like you need to meet Mr. Ohm and ask him about his Law.
raschemmel:
It sounds like you need to meet Mr. Ohm and ask him about his Law.
I heard it was repealed.... citizens complained about it being too restrictive, and that they should be allowed to have a free relationship between V, I and R.
I heard it was repealed.... citizens complained about it being too restrictive, and that they should be allowed to have a free relationship between V, I and R
Blasphemy !
That sounds like anarchy.
raschemmel:
Blasphemy !
That sounds like anarchy.
Wait till they get their hands on Pythagorus.....
JimboZA:
Wait till they get their hands on Pythagorus.....
It's a sin of the times.