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bliztkrieg
Joined: 23 Jul 2018
Posts: 20
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| problem measuring ac line freq |
 Posted: Mon Jul 30, 2018 11:48 pm |
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| Code: | #include <18f252.h>
#DEVICE ADC=10
#use delay (clock=20M)
#fuses NOLVP, NOPROTECT, HS, NOWDT, NOBROWNOUT
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
//!#define MODBUS_TYPE MODBUS_TYPE_SLAVE
//!#define MODBUS_SERIAL_RX_BUFFER_SIZE 40
//!#define MODBUS_SERIAL_BAUD 38400
//!
//!#define MODBUS_SERIAL_INT_SOURCE MODBUS_INT_RDA
//!#define MODBUS_SERIAL_TX_PIN PIN_F3
//!#define MODBUS_SERIAL_RX_PIN PIN_F2
//!#define MODBUS_SERIAL_ENABLE_PIN PIN_C3 // Controls DE pin for RS485
//!
//!#include "modbus.c"
//!
//!#define MODBUS_ADDRESS 0x01
long temp = 0;
int1 int_flag = FALSE;
int1 edge_flag = TRUE;
int1 pulse_flag = FALSE;
static unsigned int16 counter = 0;
unsigned int16 ccp_delta = 0;
static unsigned int32 dc_counter = 0;
//!unsigned int16 freq = 0;
unsigned int8 timer_counter = 0;//, timer3_counter = 0;
static unsigned int32 dc_volts = 0;
const int reg_num = 3;
unsigned int16 hold_regs[reg_num]={0x00,0x00,0x00};
#INT_CCP1
void ccp_isr()
{
if(edge_flag)
{
counter = CCP_1;
setup_CCP1(CCP_CAPTURE_FE);
edge_flag = FALSE;
}
else
{
ccp_delta = CCP_1 - counter;
setup_CCP1(CCP_CAPTURE_RE);
edge_flag = TRUE;
pulse_flag = TRUE;
}
}
#INT_CCP2
void ccp2_isr()
{
dc_counter++;
}
#INT_TIMER3
void timer1_isr()
{
set_timer3(0);
timer_counter++;
if(timer_counter == 10) //reading counter after 1 sec
{
int_flag = TRUE;
}
}
void main()
{
static unsigned int32 dc = 0;
static unsigned int16 pulse = 0;
static unsigned int16 freq = 0;
setup_adc(ADC_CLOCK_INTERNAL);
setup_adc_ports(ALL_ANALOG);
setup_timer_1(T1_INTERNAL | T1_DIV_BY_8);
setup_timer_3(T3_INTERNAL | T3_DIV_BY_8);
//! set_timer1(65535); // T = 1/fosc/4 * prescalar * (65535 - tmr)
clear_interrupt(INT_CCP1);
setup_CCP1(CCP_CAPTURE_RE);
enable_interrupts(INT_CCP1);
clear_interrupt(INT_CCP2);
setup_CCP2(CCP_CAPTURE_DIV_16);
enable_interrupts(INT_CCP2);
clear_interrupt(INT_TIMER3);
enable_interrupts(INT_TIMER3);
enable_interrupts(GLOBAL);
//! modbus_init();
while(1)
{
set_adc_channel(0);
delay_us(100);
temp = (read_adc()*4.88)/10;
if(int_flag)
{
dc_volts = dc_counter;
dc_counter = 0;
timer_counter = 0;
int_flag = FALSE;
}
if(pulse_flag)
{
disable_interrupts(INT_CCP1);
pulse = ccp_delta;
enable_interrupts(INT_CCP1);
freq = (6250000/(pulse*2));
pulse_flag = FALSE;
}
dc = ((dc_volts*6631)/100000); delay_us(200); //6631
//! hold_regs[0] = temp;
//! hold_regs[1] = freq;
//! hold_regs[2] = dc;
//! //MODBUS CODE//
//! if(modbus_kbhit())
//! {
//! //check address against our address, 0 is broadcast
//! if((modbus_rx.address == MODBUS_ADDRESS) || modbus_rx.address == 0)
//! {
//! switch(modbus_rx.func)
//! {
//! case FUNC_READ_HOLDING_REGISTERS:
//! if(modbus_rx.data[0] || modbus_rx.data[2] || modbus_rx.data[1]>=reg_num ||
//! modbus_rx.data[3]+modbus_rx.data[1]>reg_num)
//! {
//! modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
//! }
//! else
//! {
//! modbus_read_holding_registers_rsp(MODBUS_ADDRESS,(modbus_rx.data[3]*2),
//! hold_regs+modbus_rx.data[1]);
//! }
//! break;
//!
//! default: //We don't support the function, so return exception
//! modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_FUNCTION);
//! }
//! }
//! }
//! //MODBUS CODE END//
printf("temp: %lu, freq: %lu, dc: %lu\r\n", temp, freq, dc);
}
}
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hey all, i am trying to read ac line frequency but there is a problem when I'm varying AC volts (using a variac) the frequency that I'm reading is also changing. Same thing is happening on simulation as well. Can someone take a look at my code and tell me what i am doing wrong ? i have also attached schematic. Thanks in advance.
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Ttelmah
Joined: 11 Mar 2010
Posts: 19549
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| Posted: Tue Jul 31, 2018 12:29 am |
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You need to get rid of the capacitor on the input side. Use a bridge rectifier to feed the opto. Capacitors introduce lag. How this delays the opto switching point will vary with the input voltage.
Simplest circuit is:
<http://www.emergingtechs.org/p/zer.html>
Obviously adjust the resistor used based on the voltage involved. Your 10K total, suggests you are measuring a relatively low voltage, the example given, is working directly from mains.
This is surprisingly good.
A slightly better circuit is this one:
<https://www.edn.com/design/analog/4368740/Mains-driven-zero-crossing-detector-uses-only-a-few-high-voltage-parts>
Beware in all cases the operational voltage rating of the resistors involved. |
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bliztkrieg
Joined: 23 Jul 2018
Posts: 20
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| Posted: Tue Jul 31, 2018 12:41 am |
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| Ttelmah wrote: | You need to get rid of the capacitor on the input side. Use a bridge rectifier to feed the opto. Capacitors introduce lag. How this delays the opto switching point will vary with the input voltage.
Simplest circuit is:
<http://www.emergingtechs.org/p/zer.html>
Obviously adjust the resistor used based on the voltage involved. Your 10K total, suggests you are measuring a relatively low voltage, the example given, is working directly from mains.
This is surprisingly good.
A slightly better circuit is this one:
<https://www.edn.com/design/analog/4368740/Mains-driven-zero-crossing-detector-uses-only-a-few-high-voltage-parts>
Beware in all cases the operational voltage rating of the resistors involved. |
Hey thanks for your response. I have got things working like they should but i have one little problem, when i cut off the AC supply the frequency should drop down to 0 right ? Well, it is not, it is showing me the last calculated value anything that i may have missed ? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Jul 31, 2018 1:51 am |
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| bliztkrieg wrote: |
I have one little problem, when i cut off the AC supply the frequency
should drop down to 0 right ? Well, it is not, it is showing me the last
calculated value anything that i may have missed ? |
Read this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=56439&start=5 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19549
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| Posted: Tue Jul 31, 2018 1:51 am |
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No, it's not going to drop to zero.
The CCP doesn't trigger, so the last calculated value remains.
You need to add some sort of timeout to the loop. If 'pulse_flag' is not set in (say) twenty times round the loop, then set frequency to zero:
| Code: |
int8 loopcnt=0;
//then in the loop
if(pulse_flag)
{
disable_interrupts(INT_CCP1);
pulse = ccp_delta;
enable_interrupts(INT_CCP1);
freq = (6250000/(pulse*2));
pulse_flag = FALSE;
loopcnt=0;
}
else
{
if (loopcnt>=20)
freq=0;
else
++loopcnt;
}
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Every time pulse_flag is seen, loopcnt is set back to zero.
If it gets to 20 (the loop always takes over 100uSec), it'll set freq to zero. So >0.02 seconds without a pulse being seen. |
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bliztkrieg
Joined: 23 Jul 2018
Posts: 20
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| Posted: Tue Jul 31, 2018 3:30 am |
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| Ttelmah wrote: | No, it's not going to drop to zero.
The CCP doesn't trigger, so the last calculated value remains.
You need to add some sort of timeout to the loop. If 'pulse_flag' is not set in (say) twenty times round the loop, then set frequency to zero:
| Code: |
int8 loopcnt=0;
//then in the loop
if(pulse_flag)
{
disable_interrupts(INT_CCP1);
pulse = ccp_delta;
enable_interrupts(INT_CCP1);
freq = (6250000/(pulse*2));
pulse_flag = FALSE;
loopcnt=0;
}
else
{
if (loopcnt>=20)
freq=0;
else
++loopcnt;
}
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Every time pulse_flag is seen, loopcnt is set back to zero.
If it gets to 20 (the loop always takes over 100uSec), it'll set freq to zero. So >0.02 seconds without a pulse being seen. |
Thanks it worked like a charm :D |
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kx9
Joined: 05 Nov 2013
Posts: 3
Location: portland OR
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| measuring 60hz frequency |
| Posted: Tue Sep 04, 2018 12:55 pm |
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| You might want to add a hysteresis gate and divide by 2 FF after opto. This will clean up the slow edges, filter noisy signals and will make the input signal voltage intolerant. |
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