I have a application, need to measure a power supply's value and output a voltage at its half value.
The power supply has a 5.4 - 5.7 Vdc.
Thanks
How much current?
Two reistors can do that. Or maybe a pot, if you need it to be adjustable.
Thank you MorganS.
What I need is automatically fulfill the measurement and the half value voltage output.
I don't know the current number, can't be much cause of its for signal.
The power supply has a 5.4 - 5.7 Vdc.
That is a worry, it is too high to put into the 5V pin and too low to put into the Vin or the barrel jack.
EDIT I think you are meaning that is the voltage you want to measure. in which case you have to divide it by two in the first place to measure it.
You must not exceed the chips power rails ( the 5V pin for a Uno ) when feeding a voltage into an Arduino.
and output a voltage at its half value.
That will only happen at a very small current, a few mA at best.
How fast is this signal changing? Why do you want to do this, if it is a signal then it is not a power supply.
But why do you want to use an Arduino?
Grumpy_Mike:
That is a worry, it is too high to put into the 5V pin and too low to put into the Vin or the barrel jack.EDIT I think you are meaning that is the voltage you want to measure. in which case you have to divide it by two in the first place to measure it.
You must not exceed the chips power rails ( the 5V pin for a Uno ) when feeding a voltage into an Arduino.
That will only happen at a very small current, a few mA at best.How fast is this signal changing? Why do you want to do this, if it is a signal then it is not a power supply.
But why do you want to use an Arduino?
Thank you Grumpy_Mike,
Yes, the 5.4-5.7 is the voltage need be measured, and what I need is a voltage of half its value.
The voltage changes very slow, when I say its a signal mean the outputs works as signal.
To output an accurate, stable voltage value, you need a DAC (digital to analog converter). Most Arduinos do not have one.
This DAC might do the job.
laoadam:
I have a application, need to measure a power supply's value and output a voltage at its half value.
This output voltage - what output impedance do you want? How much current handling?
jremington:
To output an accurate, stable voltage value, you need a DAC (digital to analog converter). Most Arduinos do not have one.This DAC might do the job.
Thank you jremington,
Can a DAC output continuous change within a certain range say 1.5V - 3.7V controlled by Arduino?
All DACs are digital, which means that the output changes in single bit steps.
The 12 bit DAC linked above outputs 0 to 5 V in steps of about 1 mV.
Surely a simple DC OP-amp with a gain of 0.5 is all you need
laoadam:
Thank you Grumpy_Mike,Yes, the 5.4-5.7 is the voltage need be measured, and what I need is a voltage of half its value.
The voltage changes very slow, when I say its a signal mean the outputs works as signal.
Two identical resistors then. No Arduino required.
Thank you jremington, whats the different between MCP4261 and MCP4725?
Thank you jackrae and MorganS,
The signal is only used to setup a joystick PAD, and I need use Arduino to control the PAD later on.
A [u]voltage divider[/u] will (with 2 equal-value resistors) can cut the voltage in half as long as the resistors don't draw too much current, changing the voltage. ([u]Ohm's Law[/u])
And, the "load" must have much-higher resistance than the "bottom" resistor. If the load resistance is too low, it messes-up the voltage divider. This is why you can't use a voltage divider as a power-supply voltage-reducer. The Arduino's inputs have "almost infinite" resistance/impedance (~100 megohms) so a voltage divider is OK with an Arduino analog input.
If the voltage divider is going-into an Arduino analog input, in most cases you can use resistor values that sum-up to between 1K and 10K. Don't forget that resistors have a tolerance and your reference may not be "perfect" so your readings may not be perfect.
If the Arduino power supply is not stable the ADC reference voltage may not be stable and you may want to use the optional [u]1.1V analog reference[/u]. Then, you'll have to scale your voltage divider to about 1:5 instead of 1:2. The 1.1V reference isn't perfect either, but it's very stable so you can calibrate your setup for accuracy. (i.e. You can use the map() function for a simple linear calibration/correction.)
laoadam:
The signal is only used to setup a joystick PAD, and I need use Arduino to control the PAD later on.
Start with that information. Then you will get more useful information.
In what way is it controlling the pad? Is this attached to some larger system?
Hi,
What is the application?
What is the signal from?
Why do you need it to be halved in value?
Why can't you use a simple potential divider?
Thanks.. Tom.. 
MorganS:
Start with that information. Then you will get more useful information.In what way is it controlling the pad? Is this attached to some larger system?
Thank you MorganS.
Ya, I gonna to use another Arduino and 433MHz RC pair modules control the PAD by the interface of a Arduino + a DAC.
TomGeorge:
Hi,
What is the application?
What is the signal from?
Why do you need it to be halved in value?
Why can't you use a simple potential divider?Thanks.. Tom..
Thank you TomGeorge,
The application is to use Arduino + 433MHz RC to control a car. The signal come from a joystick.
The another question here is the joystick can move a large tilt say from 1V to 4.5 V, but I just need a little number range say 1.75V to 3,75V.
gonna to use another Arduino and 433MHz RC pair modules
These sorts of RC pairs in general don’t deal with analogue levels they normally just deal with digital signals. That means you need to modulate any analogue data in a suitable manner, for example as a PWM signal.