I'm trying to make a multi-function program that acts as both a frequency counter (512 Hz range) and a voltage level reader. I've written the code for the frequency counter, and it functions fine on it's own, but as soon as I add an analogRead function to test the voltage it messes up my frequency count. I've tried adding delays before and after calling the frequency function, but this caused greater error in my results. I'm thinking that the delay created by the analogRead function is interfering with the frequency counter code, but shouldn't the for loop negate that?
bool cur_Val = false;
unsigned long cur_Time = 0;
unsigned long old_Time = 0;
bool old_Val= false;
unsigned long time_arr[200];
int counter = 0;
unsigned long freq = 0;
unsigned long test_Freq();
void setup()
{
Serial.begin(9600);
pinMode(5, INPUT);
pinMode(13, INPUT);
}
void loop()
{
Serial.println(analogRead(5));
Serial.println(test_Freq());
}
unsigned long test_Freq()
{
for(; counter < 199;)
{
cur_Val = digitalRead(12);
if(old_Val == 0 && cur_Val == 1)
{
cur_Time = micros();
int time_Delta = cur_Time - old_Time;
time_arr[counter] = time_Delta;
counter++;
old_Time = cur_Time;
}
old_Val = cur_Val;
if (counter == 199)
{
unsigned long sum = 0;
for(int i = 0; i < 200; i++)
{
sum = sum + time_arr[i];
}
freq = 1 / (.000001*(sum / 200));
}
}
counter = 0;
return(freq);
}
So do you think this delay is what's throwing off my frequency counter code? I originally wrote the frequency counter code in the main loop, but I was encountering this issue so I thought I'd try a for loop. I figured if I put the code into a for loop, and called it in a separate function it would run exclusively and avoid any time delays created by other code... but my results are identical. My frequency count is thrown off by -8Hz. I'm assuming some sort of delay occurs during the loop causing it to miss cycles of my test frequency when I add that function.
As for
pinMode(5, INPUT);
I'm using analog pin 5 for my voltage test. Maybe the pin initialization isn't necessary, but I don't think this is related to my issue.
So I tried removing Serial.println(analogRead(5)); , and replaced it with just (analogRead(5)); and the problem went away. This still begs the question of how I can return the results of the voltage test without messing up my frequency count.
It isn't.
An analogue input is just that - an input, so no need to set the mode. (unless you want to use it as a digital pin, in which case, you use a different pin number).
well I tried increasing the serial baud rate to 57600 and now it seems to work fine! I still find it strange though
At 9600 baud, one character takes about 1ms to transmit, and the call is blocking...until the very last character has been written to the UART, when the functon returns.
When you say nesting, are you referring to how I call test_Freq() from within a print command? If this is the case, you'll notice that the function test_Freq() is returning the value in variable freq, which is the calculated frequency. Basically the function test_Freq() is called and returns a value to the print function.
Looking at the code I would simplify a few things (highlighted).
Question comes in my mind if time_arr[] is not needed as you can calculate the sum directly at very low costs. But the individual values may be usefull when extending the application.
[glow]unsigned long sum = 0;
unsigned long freq = 0;[/glow]
void loop()
{
cur_Val = digitalRead(12);
//Serial.println(cur_Time);
if(old_Val == 0 && cur_Val == 1)
{
cur_Time = micros();
int time_Delta = cur_Time - old_Time;
//Serial.println(time_Delta);
time_arr[counter] = time_Delta; [glow] // not needed ??[/glow]
[glow] // calculate the sum immediately
sum += time_Delta;[/glow]
//Serial.println(time_arr[counter]);
counter++;
old_Time = cur_Time;
}
old_Val = cur_Val;
if (counter == 199)
{
// Serial.println(sum);
//Serial.println(sum/100); [glow]<== why /100 iso /200 !! 200 measurements
[/glow]
freq = 200 * 1000000 / sum; [glow]// simplified floating point to int math[/glow]
Serial.println(freq);
Serial.println(analogRead(5));
// Serial.println("");
// reset all
counter = 0;
sum = 0;
}
}
there is an array element [199], but is there a valid value in it?
No it isn't , look at the code-snippet below and set your mental "counter" to 198.
time_arr[counter] = time_Delta; [glow]COUNTER = 198[/glow]
//Serial.println(time_arr[counter]); [glow]FILL time_arr[198] 199 is not filled[/glow]
counter++; [glow]COUNTER = 199[/glow]
old_Time = cur_Time;
}
old_Val = cur_Val;
if (counter == 199) [glow] YES IT IS !![/glow]
{
unsigned long sum = 0;
unsigned long freq = 0;
for(int i = 0; i < 200; i++)
{
sum = sum + time_arr[i]; [glow]HERE [199] IS USED
[/glow]
if (counter == 199) => if (counter == 200) would improve it
You guys were right on all counts. I've modified the code using your changes and it seems to be working a lot better. I have found, however, that the frequency counter still isn't quite accurate - a 512Hz signal reads 512, but a 513 Hz signal reads 512 still. A 514 Hz signal reads correctly... and I get the same results with frequencies lower than 512 Hz. Any ideas why? Thanks again for all the help!