Transmitting AC Signal to μC for ADC: Exploring DC Offset Options

[phyky]

Homework Statement

how can i transmit ac signal to μC to further ADC?

Homework Equations

The Attempt at a Solution

can i use dc offset?

 

[berkeman]

Homework Statement

how can i transmit ac signal to μC to further ADC?

Homework Equations

The Attempt at a Solution

can i use dc offset?

If I understand your question, yes. You can add a DC offset equal to half the expected peak-to-peak AC voltage (Vpp) to effectively convert it to a mono-polar time varying signal that a standard ADC could deal with.

 

[earlofwessex]

be aware that uC ADC conversion times can be slow, you may want to consider a stand alone IC

 

[phyky]

what is stand alone IC?

 

[berkeman]

be aware that uC ADC conversion times can be slow, you may want to consider a stand alone IC

what is stand alone IC?

He is referring to the A/D converter functionality. That can either be an integrated part of the microcontroller (uC) chip, or it could be a separate ADC chip. I think he is saying that ADCs on typical uCs have limited performance, so you might consider using an external/separate ADC chip, which you would interface to your uC via the IO lines of the uC (either using I2C or SPI serial protocols, or some parallel interface protocol).

 

[phyky]

i see. if i use dc offset, is the output voltage ll become varies in ADC?or i need ac to dc converter is better?

 

[earlofwessex]

thankyou berkeman that is what i meant.

phyky, your application here is quite vague, and the best solution depends on things you haven't told us. any adc, a built in peripheral of a uController or a separate IC will be limited by the maximum samples per second. for example, dsPic33F4013 has a maximum of 200 ksps.

if you want to measure an ac signal of frequency 20kHz, you will only get 10 samples per cycle, which is enough to estimate the frequency and peak amplitude, but not enough to analyse distortion or check for harmonic content.

if on the other hand you want to measure 100kHz, its not enough to do anything but check that the signal is there, and possibly measure frequency within a failry large error margin. you will find it very difficult to measure the peak amplitude, and impossible to distinguish between a square wave and a sine wave without some other knowledge of the signal.

you also have to consider resolution, which may or may not affect you depending on what you wish to measure.

 

[phyky]

i m doing computer interfacing. the microC connect to my computer.it is a built in microC with 10 bit ADC module.
- Auto-acquisition capability
- Conversion available during Sleep
- Internal 1.024V Fixed Voltage Reference (FVR) channel
- Independent input multiplexing
so i need convert the ac to dc?

 

[earlofwessex]

its highly likely yes.
look in the microcontrollers datasheet, it will should you the ranges that the adc can convert