I have a 0 to 5V ADC which work well with my PIC microcontroller.
My problem is i need to measure a non sinusoidal AC voltage using the ADC.
Anyone can help me?
One more question... where should i place the ground reference for the AC? TQ!
The simplest way is to use a two-resistor voltage divider, reduce the AC voltage to 0-5V and impose 2.5V dc offset, so if the input AC voltage is 0V the ADC input "sees" 2.5V ..
my input signal look like an square wave AC with a spike at the falling edge of each pulse..
the voltage (including the spike which i need to measure) is around +/-12V...
i'd have a 0 - 5V ADC with PIC...
how do i produce a rms voltage of the signal?
Not only do you have to use a resistive divider as stated above to reduce the peak to peak levels below the 5 V range of your converter, but you have to add a DC offset to the signal. This can be done by connecting the midpoint of the divider to the 5 V through another resistor. It is a simple matter of algebra to get two of the resistor values once you select the value of the third one.
i think spike have very high rise and fall time and they are of very short duration i am doubtfull that adc will able to have atleast two samples of spike u must use flash adc
and ofcourse all above accessories to limit level that adc can handle
a simple way is to design a new adc forhigher resolution or if u want to mesure ac put it down to 5v ac using 6M resistance in circuit then u can connect it directlt to PIC inputs & pic will sample it for u
or connect the 5v ac to mic input of PC & using visual analyser8 s/w or matlab u can messure the signal & process it
first convert the AC to DC using an RMS to DC converter or using a conventional full wave rectifire. The using ur adc measure this value. Use a step down stage if required.
Thanx Guys.. I need some clarification though..
The AC that i'm going to measure is used for something else...
If i connect this to full wave rectifier and ADC, will this affect its operation?
To interface an AC signal to an ADc u need to first convert the same to DC level using a true rms to Dc converter IC or, a precision rectifier circuit.
For example if ur ac signal is 2 volt pk-pk
then its rms value in case of sine will be=.707V
An rms to Dc converter will output .707v DC signal which will be read by ADC.