Help me measure the voltage of a signal and display it on LCD

hia frnzs
me wanting to design a circuit to measure the voltage of the signal having following specification:
voltage range : 0-9.99v
frequency : 1khz/10khz/100khz/500khz
and display it on lcd screen.please help me out for how to mesure the voltage of this signal.

waiting for response
thankx
shaz

measure voltage

You could use the internal AD-Converter of a PIC / AVR / other uC, with a (precision) resistor network as a voltage divider to protect the uC. For a higher accuracy (most internal adc's are 8 bit versions), you cold use a standalone ADC and interface it to some uC of your choice. What kind of LCD are you thinking of?

measure voltage

thanks buzzz for replying dear but that i know i have to use adc with microcontroller.the problem is with circuit daigram before adc ...the voltage divider which u r saying..can u explain it to me more or provide me the ckt daigram

Re: measure voltage

Well, you are trying to measure a voltage of 0 to 10 volts (9,99V). Assuming you are using a 5V powered uC, you could divide the voltage you want to measure by 2, using two 10k resistors (eg 1% metal film if you don't need mega-precision) in series. Attached an image for clarification.
You will need to make sure the measured voltage will _never_ exceed 10V, or you need to build some extra protection.

measure voltage

Thanks for replying buzz. But my actual problem is a type of voltage signal, "It's not DC". it's an AC signal of different frequencies. it can be 1khz or 10khz or 100khz or 500khz (and not 50 Hz). Please help me out.
Thanks

Re: measure voltage

y said about freq,
what about the waveform?
sin, sawtooth, pulse train ...

assumin V(t)=sin(wt) you can use a simple peak detector made by a diode, capacitor and a resistor.
if the method is not so presicion, u can use multipliers (analog or digital) to calculate V(t)^2 an then use a simple low pass filter (analog or digital) to find rms of the voltage. this is exact value for rms, accordind to rms definition.

BEST!

Re: measure voltage

shaz said:

Thanks for replying buzz. But my actual problem is a type of voltage signal, "It's not DC". it's an AC signal of different frequencies. it can be 1khz or 10khz or 100khz or 500khz (and not 50 Hz). Please help me out.
Thanks

Click to expand...

Woops... That would mean that with a simple resistor network, all mathematics would need to be done inside uC, realtime that is...
I've been doing some quick googling for you, but in my (very quick) search, I cannot find any manufacturer that produces some kind of useful chip for this.... Maybe you could try and get your hands on a schematic of some kind of multimeter-alike device?

Re: measure voltage

Thanks goodboy_pl & buzz for replying.....buzz after reading your mesasage i feel it's quiet difficult to design this circuit....but what goodboy_pl wirtes i think it can be done, right??? goodboy_pl can you please elaborate a bit more on the calculation part which i think can be done inside the microcontroller. Recently i found a peak detector ciruit on this site please check this if it would work. the signal waveform is Sinewave. my main problem is the frequency of the signal.

thanks

Re: measure voltage

I haven't thought of a peak detector, shame on me!
You could connect the peak detector to a digital input of the uC (assuming that your detector will be 5V out max), and when it becomes high, you start an internal counter of the uC. When it becomes high again (so check that it's been low before!), you stop the timer. Convert the number of counts of the timer to milliseconds, depending on prescaler and oscillator speed, and you have your high time. This can easily be converted to a frequency when your signal is a sine wave, 50% duty cycle. When it's not, it gets more complicated, but not impossible... Then you would need to measure the low time on another channel, and calculate the same thing. Frequency can be extracted again with that information.
To get an average, count eg 10 or 100 signal changes before stopping the timer.
To measure voltage, you would still need the ADC of the controller, this will be a totally separate subroutine offcourse.
Hope it makes sense, I'm not that good in explaining brainstorm-ideas... :wink:

measure voltage

Note that your freq is 500 KHz and that peak detector must be carefully checked before applying - make a simulation before . As far as 2nd opamp just gives feedback on DC first one must have high slew rate .
One tutor. says about 20 V/usec. But i suppose that this wont be enough for 500 KHz freq .