Hi everybody,Can someone please tell me how much time does getadc(x) command(Basic language) take in microsecond? (8 Mhz oscillator Atmega8)
Thanks.

 

Hi everybody,Can someone please tell me how much time does getadc(x) command(Basic language) take in microsecond? (8 Mhz oscillator Atmega8)
Thanks.

Put a 50 consecutive getAdc(X) commands together and then toggle an LED on then another 50 reads and then toggle off (100 total per flash). If you can see individual flashes, use an oscilloscope. Adjust the number of reads between toggles.

 

Put a 50 consecutive getAdc(X) commands together and then toggle an LED on then another 50 reads and then toggle off (100 total per flash). If you can see individual flashes, use an oscilloscope. Adjust the number of reads between toggles.

Ingenious idea!Thanks, But There is no oscilloscope!Maybe I can use Incr variable in The loop and toggle pin after for Example var equal to 30 and divide total toggle time to 30.

 

Ingenious idea!Thanks, But There is no oscilloscope!Maybe I can use Incr variable in The loop and toggle pin after for Example var equal to 30 and divide total toggle time to 30.

There are lots of options, just develop one that works for you and the tools you have. Loops take a lot of time as well so make sure you account for the core (instruction set) level clock cycles needed for those as well.

I am surprised that documentation is not available for your question but it may be easier to measure. If you have enough program memory, you may be able to measure with a stopwatch to some reasonable level of accuracy. 5000 or 50000 ADC steps per LED toggle.

 

There are lots of options, just develop one that works for you and the tools you have. Loops take a lot of time as well so make sure you account for the core (instruction set) level clock cycles needed for those as well.

I am surprised that documentation is not available for your question but it may be easier to measure. If you have enough program memory, you may be able to measure with a stopwatch to some reasonable level of accuracy. 5000 or 50000 ADC steps per LED toggle.

Thankks,I am calculating the getadc duration with following code,but I think " incr" takes time too! Green indicates stopwatch start,Red incdicates stop.


dim w as word,n as long
red=0

Wait 6
Green = 1

Do
N = 0
Do
W = Getadc(0)
Incr N

Loop Until N > 200000
Toggle Red

Loop

 

$regfile = "m8adef.dat"
$crystal = 8000000
Config Adc = Single , Prescaler = Auto , Reference = Internal ' '
Enable Adc
Start Adc

Config Portd.4 = Output
Config Portd.3 = Output
Green Alias Portd.3
Red Alias Portd.4


Loop with getadc():

Wait 6
Green = 1
Do
N = 0
Do
W = Getadc(0)
Incr N
Loop Until N >= 500000
Toggle Red
Loop
Time to red on = 1: 54.00 = 114000000 us
114000000 / 500000 = 228 us (Each cycle takes)


Loop without getadc():

Wait 6
Green = 1
Do
N = 0
Do
Incr N
Loop Until N >= 500000
Toggle Red
Loop
Time to red on = 0 : 3.58 = 3580000 us
3580000 / 500000 = 7.16 us (Each cycle takes)


228 - 8 = 220 us Time getadc() takes
I did not think it takes such a long time!

 

I forgot to dimension variables in previous post

 

Digitize a 500Hz square wave signal and see how many high samples you get in 1ms duration.

 

Digitize a 500Hz square wave signal and see how many high samples you get in 1ms duration.

0.5 cycle and 1 peak

 

 

0.5 cycle and 1 peak

Wrong answer.
Examine the sampled data points and count how many data points are contained in the high portion of the wave.

 

Another way of finding the sampling rate, if you have the necessary equipment, is to determine the Nyquist frequency x 2.

Input a sine wave signal and observe the reconstructed waveform.
Starting at a low input frequency, say 100Hz, slowly increase the frequency until you observe that the reconstructed frequency reaches a maximum value and then diminishes to 0Hz, i.e. constant DC voltage. This frequency is equal to your sampling frequency.