10F222 Wake on pin change

[Charlie]

Brand new batteries will actually put out more than 1.5V. I'd recommend the diode. Also helps for the day you accidentally put them in backwards. Or use NiCDs.

[Demon]

Would a low drop off 7805 help?

Robert

[Charlie]

How low is low? They usually need over a volt. Can you point to a spec sheet?

[HenrikOlsson]

Hi,
I don't really see the point of linear regulator. A 5V one, LDO or normal, will drop out of regulation pretty quick, then it behaves as if it wasn't there in first place - or worse. Using a lower voltage like 3.3V or 2.5V will only turn useful energy into heat in the regulator so that's no good either.

The "best" way would of course be a switching type boost/buck converter/regulator so that the PIC can be fed 2.5V (or whatever) from "any" supply voltage, the good thing about this is that the PIC Draws much less current at lower supply voltages so provided the converter/regulator is efficient you'd get more use out of the batteries. But, it adds complexity so.....perhaps use 3 cells in series instead of 4.

/Henrik.

[Demon]

How low is low? They usually need over a volt. Can you point to a spec sheet?

I haven't used one yet. I checked a few and can't find one that comes even close to what is needed here.

They should call them NAMDO; Not As Much Drop Off instead of LDO.

Robert

[HenrikOlsson]

Hi,
For reference, the LP2950 has a maximum specified drop out voltage of 450mV @100mA load and 80mV @100uA. But like I said, for this application, I don't think using a linear regulator is a good idea.

The quiescent current of the regulator alone (the LP2950 that is) is 75uA which isn't much but it means that the regulator alone pulls like 50-100 times more current than the PIC does when it's sleeping.

/Henrik.

[LinkMTech]

This is part of a program I used to put a PIC16F685 to sleep running at 8MHz.
The unit runs on a CR2032 coin cell and managed to get it down to less than 50nA in Sleep mode.

I had to make sure the circuit was not going to be sourcing power to anything while on standby and it's important to shut things OFF before bedding down.

I read somewhere that the @ NOP after the @ SLEEP would be needed and found it would not stay asleep unless it was there. Hey, as long as it worked!

'=========================================================================
'                           SLEEP Mode
' This routine provides an Ultra Low power consumtion until a button is
' pressed. All I/O's are setup for the PORTA/B Interrupt On Change function
' prior to going into standby condition. Any state change detected to these
' PORTs starts main and directs to proper routine.        
'=========================================================================
 Sleep_mode:
    OPTION_REG.7 = 0    ' Global weak pull-up enable bit enabled
    WPUA = %00011111    ' Weak pull-ups enable on PORTA inputs except RA5
    WPUB = %00000000    ' Weak pull-ups disabled on PORTB
    MOSI = 0            ' Turn OFF SPI data line
    _CSN = 0            ' Turn OFF module select line
    TXEN = 1            ' Transmitter Vcc OFF
    SEND = 0            ' Turn OFF MS encoder SEND input
    Action = 0          ' Turn OFF all outputs
    m = 0               ' Mode counter reset
    IOCA = %00000110    ' Mode input pin RA4 configured for IOC.
    IOCB = %10000000    ' ID_new input pin RB7 configured for IOC.
    Store_A = PORTA     ' Reads PORTA
    Store_B = PORTB     ' Reads PORTB
    INTCON = %00001000  ' RABIE (RA and RB Interupt Enabled)
    @ SLEEP             ; Goes mimi until a change of state is detected
    @ NOP               ; 1 instruction cycle