Hi,

I have a pic 16F628 circuit, and when a button is pressed, it triggers a relay.

Now I want to add a new feature; when the time is out, I want a piezo to buzz for 2 seconds. I have a 555-timer based piezo buzzer, and when I connect it to the pic and reprogram it, it's making a buzz. Just as I want.

But isn't it possible to connect the piezo directly to the pic? I think I've read somewhere, and seen some source code about that, but now I cannot find it.

Anyone?

 

What language are you using?

make a pin high, wait 1ms, turn pin low, wait 1ms, repeat 250 times for a 1/2 second tone. Vary the times for different frequencies.

 

Yeah, just as I thought, some info missing.

I'm using MPLAB and Hi tech C.

So by turning a pin "on and off" really fast makes a tone?

for(i=0;i<250;i++)
{
pin high
delay_ms(1);
pin low
delay_ms(1);
}

Something like this?

 

That's a low tone, for a speaker. You may want to make a low pass filter on the output to smooth it out a bit. like a 100 ohm in series with output pin and maybe a 0.1uF cap from that resistor to ground. This makes the sound a tad "cleaner" on a dynamic speaker. If you are using a piezo, you may need to tweak the components to cut off under 20kHz.

 

Thanks.

I think this will do. I just want to hear when the time period of the relay end.

 

Let me know if it works. I haven't done it in so long that I forgot the exact values, as well as what I used for a lowpass.

 

OK. I will let you know, by posting the result in this thread. I will do it in the evening on thursday the 25.11.10.

 

I'll be here. Include source code, schematic and board photos for completed projects area. This would be a good example for others getting going in PIC programming.

P.S. Try out BoostC! They have a ton of examples, and it is what I am most familiar with.

 

I'd recommend a resistor as the capacitance of a piezo is a lot higher than the 50pF recomendation for pin loading. It might cause overcurrent and possibly resetting. I can't figure out the maths to work out how big the resistor should be.

 

 

Hi.

This circuit I'm planning to use in my new UV-exposure box. The software is just made as an example. I will use Port A as input, and Port B as output. RA6 is now set to light the LED for just 2 seconds. This will be the test button. RA7, RA5-RA0 will have different values, so with a switch, I'm able to change the trigger-port, and still just have two buttons. Test and on.

This is the software, so far:

/* 
 
Program:        main.c 
Description:    Timer program for UV-box 
PIC:            16F628 
IDE:            MPLAB 
Compiler:        Hi - Tech C 
Date:            Nov 2010 
Author:            Jens Christoffersen 
web:            www.nerdegutta.org 
 
*/ 
 
#include <htc.h> 
#define _XTAL_FREQ 4000000 
 
/* Configuration */ 
 
__CONFIG    (WDTDIS & 
            PWRTEN & 
            MCLREN & 
            BOREN & 
            LVPDIS & 
            DATUNPROT & 
            UNPROTECT & 
            INTIO); 
 
/* Prototyping the functions */ 
void lightLED(); 
void beep(); 
 
/* Global variables */ 
unsigned char i; 
 
/* Functions */ 
void lightLED() 
{ 
    PORTB = 0b00000001; // Setting bit 0 to HIGH 
    __delay_ms(1000); 
    PORTB = 0b00000000; // Setting all bits to LOW 
} // end lightLED 
 
 
void beep() 
{ 
    for (i=0;i<250;i++) 
    { 
        PORTB = 0b00000010; // Setting bit 1 to HIGH 
        __delay_ms(1); 
        PORTB = 0b00000000; // Setting bit 1 to LOW 
        __delay_ms(1); 
    } // end for-loop 
} // end beep 
 
/* Main program */ 
void main() 
{ 
TRISA = 0b11111111;    // Setting all bits on port a to input 
TRISB = 0b00000000;    // Setting all bits on port b to output 
 
PORTA = 0b00000000; // Setting all bits on port a to LOW 
PORTB = 0b00000000;    // Setting all bits on port b to LOW 
 
CMCON = 0x07;    // Disabling the analogue comparators 
 
while (1) 
{ 
    if (RA6) 
        { 
        for(i=0;i<2;i++) // Create a delay for 2 minutes 
        { 
            lightLED(); 
        } // end for-loop 
        beep(); 
        break; 
        } // end if 
 
} // end while 
 
}  //end main

I have not yet implemented the other time procedures.

As you can see, I'm using the internal oscillator.

I've made a schematic, and taken a picture, see attachment. I'm not quite sure about the connections on the schematic. I made the breadboard first, then I drew the schematic. Yes, I know - A little backwards...

The piezo is connected to pin 7, and there is no resistor. I tried with some resistors, with different values, and the result was the volume of the beep. Haven't tried a speaker.

The powersource is for the moment a "jump-started" PC power supply. When I make the PCB I will include a .01uF and a 100uF capacitor over the LM7805.

Comments are welcome.

 

The piezo will likely be the louder solution for this.

 

The piezo will likely be the louder solution for this.

Yes, and I guess that it is more space saving.

I don't want a big box. I want it as small as possible.