Startup power higher than while program running - why?

[flotulopex]

OKay now,

After y few different tries, I connected: PIC - 1µF - Piezo - R33 - Vss.

Sound is very good; current drawn by piezo is about 8mA.

I have attached both signals results (signal directly from PIC and signal after the 1µF cap).

Sougata,

I've tried to do as you said. But without the cap, it just does the same as before (current stays 50mA until I press a button).

I don't understand your comment about the variables initialisation. Is my "INIT" piece of code not correct?

[sougata]

Hi,

As you mentioned that after you press a button then the current goes down. You have also found out that it is the buzzer that is drawing the current. So when you are starting up your PIC if the port is set to an output you expect a low. If that was true then with the other end connected to VSS rules out any possibilities of drawing current. So the port is not low as expected. This is what I meant. You should always setup the initial states of the port yourself. The capacitor is acting as a DC blocking only and thus even if your port is high at startup it prevent current draw from the PIC. An interesting phenomena could be excessive switching noise at the PIC port (which starts as a input by default ), your buzzer can actually create signal if it is vibrated. Connect your scope to its ends and tap it to see for yourself. But that will not cause so much of current drain due to the internal CMOS structure switching with noise. So I still doubt what is the state of the pin when first start it up. 16F88 has got onboard peripherals which are connected to the same pin. Hope I have made myself clear this time.

[sougata]

Hi,

As you mentioned that after you press a button then the current goes down. You have also found out that it is the buzzer that is drawing the current. So when you are starting up your PIC if the port is set to an output you expect a low. If that was true then with the other end connected to VSS rules out any possibilities of drawing current. So the port is not low as expected. This is what I meant. You should always setup the initial states of the port yourself. The capacitor is acting as a DC blocking only and thus even if your port is high at startup it prevent current draw from the PIC. An interesting phenomena could be excessive switching noise at the PIC port (which starts as a input by default ), your buzzer can actually create signal if it is vibrated. Connect your scope to its ends and tap it to see for yourself. But that will not cause so much of current drain due to the internal CMOS structure switching with noise. So I still doubt what is the state of the pin when first start it up. 16F88 has got onboard peripherals which are connected to the same pin. Hope I have made myself clear this time.

[flotulopex]

Okay, I'll init it LOW.

It was now clear to me.

Checking this out now...

You're right - now it works fine.

Actually, I noticed that all PORTBs are driven HIGH for one second when I power-up the circuit. I initilize them to LOW but this happens after the register setting.

I don't think it would make sense to set the PORTBs LOW before the registers are set, does it?

[sougata]

Hi,

Could you please insert the following lines in your register settings:

SSPCON.5   = 0                  ' DISABLE THE SYNC.SERIAL.PORT AND USE AS I/O
TRISB      = %11000000
PORTB      = 0                  ' Init PORTB to low

Portb.5 is shared with the onboard Synchronous Serial Port. Turning off bit 5 of the SSPCON registers turns off this peripheral and configures it as general I/O.

[flotulopex]

Sougata,

I think my SSPCON register is already set but, just to make sure, am I right to say that in the PIC's datasheet, the register settings have default values I can read like here "R/W-0" and it would mean that the bit is set to 0?

REGISTER 10-2: SSPCON: SYNCHRONOUS SERIAL PORT CONTROL REGISTER (ADDRESS 14h)
R/W-0 R/W-0 R/W-0   R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
WCOL  SSPOV SSPEN(1)CKP   SSPM3 SSPM2 SSPM1 SSPM0
bit 7                                       bit 0

[sougata]

Hi,

The default when the PIC starts is SSPCON turned off. But you mentioned that your portb is keeping high for sometime from start. There has to be a logical reason why. I do not have a 16F88 lying so cannot give it a try myself. May be I should give a closer look to your code.

[flotulopex]

Sougata,

Thank you for confirmation.

As said in a previous post, I have solved the problem by putting a 1µF cap in serie with the BUZZER.