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[Reply #30 on:]

here is a "peak detector":
http://www.falstad.com/circuit/e-555monostable.html
(it works better than my RC-plan) :-)

but u need the negative part of ur AC signal... so u dont need any rectification, because of the horizontal capacitor...

for a 3.2kHz signal the horizontal capacitor should be 100nF and the vertical cap should be 150nF...

-arne

[Reply #31 on:]

You also need to ensure the voltage on the Arduino input pin does not exceed 5 volts. There are many ways to do that, for example using a transistor (Grumpy_Mike explained this your “DC to the Arduino” thread) or you could use an opto-isolater.

oh
that's great, i am going to try this
let see what we can see

here is a "peak detector":
http://www.falstad.com/circuit/e-555monostable.html
(it works better than my RC-plan)

but u need the negative part of uc AC signal... so u dont need any rectification, because of the horizontal capacitor...

for a 3.2kHz signal the horizontal capacitor should be 100nF and the vertical cap should be 150nF...

-arne

Thanks for your advise, but i don't know about 555 timer, it is kind of difficult
i will try it anyway, thanks
let see what it can show me

[Reply #32 on:]

u could try this, too:
http://arduino.cc/en/Reference/AttachInterrupt
the short peak should trigger the interrupt safely...
then u just measure the time between the interrupt calls...

but looking for a peak should be good, too:

Code:

const uint8_t pin = 5; // digital pin #5
void setup() {
  Serial.begin(115200);
  pinMode(pin,INPUT);
  digitalWrite(pin,HIGH); // pullup
}
void loop() {
  uint32_t sts = micros(); // start time stamp
  const uint32_t c = 1000; // wait for 1000 pulses
  for (uint32_t i=c; i>0; i--)
    pulseIn(pin,HIGH);
  uint32_t ets = micros(); // end time stamp
  Serial.println(c*1e-3/(ets-sts)); // output kHz
}

this circuit should be good in order to protect ur arduino:
AC signal ---- diode anode
diode cathode ---- 100k resistor lead A
100k resistor lead B ----- NPN transistor base
NPN transistor emitter ---- arduino ground
NPN transistor collector ----- resistor 1k lead A
resistor 1k lead B ------ arduino pin #5

dont forget this:
external circuit signal ground ----- arduino ground
(but make sure that this doesnt cause a short circuit (e. g. when the external circuit uses USB 5V as ground and USB ground as -5V power supply)... :-)

-arne

[Reply #33 on:]

oh
this

Code:

Serial.println(c*1e-3/(ets-sts));

should be this (because ets-sts r _u_secs)

Code:

Serial.println(c*1e3/(ets-sts));

:-)

-arne

[Reply #34 on:]

HELP!!
this code below still could not show the frequency. it keeps showing a number, god knows where it comes from. the number is around 45.19

whether there is sensor connecting to the analog or not

Code:

int analogPin = 1; //sensor input is analog pin 1
int val = 0 ;
long timeStart, timeStop;
#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);


void setup() {
  pinMode(analogPin, INPUT);
   lcd.begin(16, 2);
  Serial.begin(9600);
  
}

void loop()
{
  
val = analogRead(1);     {
      if (pulseIn(val, HIGH)); {
        // wait until pin goes high
       timeStart = micros();
        // wait until input goes low again
        while (pulseIn(val, LOW) ); {
        // take the actual time in microseconds
        timeStop = micros();
        // the timedifference is the the time between two rising
        // edges of the input pin (= 1 period)
        int timeStart1 = timeStop-timeStart;
        // normally the result is > 0, otherwise the
        // function micros() had an overflow (every 70 min)
        // the discard this measuring (or correct the value)
        if (timeStart1 > 0) {
          // calculate frequency
          // 1000000 microseconds/second, f = 1/t
          double f = 1000000.0/timeStart1;
          // report the measured frequency
          lcd.println(f);
          delay(1000);  
          lcd.clear();
         }
      }
      }
}
}

[Reply #35 on:]

Code:

void loop()
{
val = analogRead(1);     [glow]{[/glow]

What's this curly brace for?

Code:

     if (pulseIn(val, HIGH))[glow]; {[/glow]

Are you sure you want that semicolon there?

Code:

       // wait until pin goes high
       timeStart = micros();
        // wait until input goes low again
        while (pulseIn(val, LOW) )[glow];[/glow] {

What about this one?

The pulseIn function returns a value. The value is how long it took the pulse to go HIGH or LOW. You will get misleading results if you do not use that time.

[Reply #36 on:]

Thanks Paul
i have cancelled all the ";"
however, it still keeps showing me a number
it is much larger, around 30-900
what did i do wrong ?

[Reply #37 on:]

i have cancelled all the ";"

Well, that probably wasn't the greatest idea.

Post your current code.

[Reply #38 on:]

here it is
thanks

Code:

int analogPin = 1; //sensor input is analog pin 1
int val = 0 ;
long timeStart, timeStop;
#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);


void setup() {
  pinMode(analogPin, INPUT);
   lcd.begin(16, 2);
  Serial.begin(9600);
  
}

void loop()
{
  
val = analogRead(1);  
      if (pulseIn(val, HIGH)){
        // wait until pin goes high
       timeStart = micros();
        // wait until input goes low again
        while (pulseIn(val, LOW) ) {
        // take the actual time in microseconds
        timeStop = micros();
        // the timedifference is the the time between two rising
        // edges of the input pin (= 1 period)
        int timeStart1 = timeStop-timeStart;
        // normally the result is > 0, otherwise the
        // function micros() had an overflow (every 70 min)
        // the discard this measuring (or correct the value)
        if (timeStart1 > 0) {
          // calculate frequency
          // 1000000 microseconds/second, f = 1/t
          double f = 1000000.0/timeStart1;
          // report the measured frequency
          lcd.println(f);
          delay(1000);  
          lcd.clear();
         }
      }
      }
}

[Reply #39 on:]

Please read this:
http://arduino.cc/en/Reference/PulseIn

The first argument to pulseIn is the pin to measure, not some value read from that pin.

[Reply #40 on:]

The first argument to pulseIn is the pin to measure, not some value read from that pin.

umm
so i am just giving a pulse to the pin, not reading it?

how can i read pulse   ?

[Reply #41 on:]

Where is the pulse coming into the Arduino? To some pin, presumably. Pass that pin number to pulseIn.

[Reply #42 on:]

Where is the pulse coming into the Arduino? To some pin, presumably. Pass that pin number to pulseIn

i think that is digital 8 or 9
when i took out the digital 8 and 9, the screen show me nothing
but how to pass the pin ?
there should be no pulse in the first place, due to the fact that i didn't connect the sensor output to the arduino
however, it keeps showing a number , i don't know what the pulse is

i am sorry about that Paul, that i was off, it's because i gotta be out of the school, i am home now, and thanks, please keep talking to me

could some one guide me to do the program?
i very appreciate it, it is my final project, i may not get a pass if i couldn't do it

[Reply #43 on:]

ah
hey guys, i found something
there is nothing shown, if the arduino analog 0 is connected to the LCD analog 0
if i took out the analog input, the number is coming out again.
someone know what is happening ?

could anyone help me checked the program, is it correct that
the frequency can be determinated from the analog pin 1 ?
and the pin 1 is connected to the sensor.

Thanks everyone

[Reply #44 on:]

if the arduino analog 0 is connected to the LCD analog 0

What sort of LCD are you using that has an analogue input?

the frequency can be determinated from the analog pin 1 ?

Analogue pin 1 (what's wrong with analogue pin zero?) can be used with "pulseIn", but you have to number it as a digital pin in your sketch.
It's digital pin 15.