ON/OFF button for PIC16f877a (ambiguity)

[Charlie]

To expand on what Henrik said, you could be in trouble at any time, not just during power up. The ADCO signal needs examination, and could possibly need some resistance and protection diodes.

Is there still more to the circuit you are not showing? Where does the power come from and what are those circuits?

[irilias]

Thank you gentlemen for your replies, much appreciated ..
That's the whole thing that i've attached ( Conditioning Circuit "Amplification + filtering .." and the Command Circuit "Motor + electrovalve .." )
besides the LCD and MMC interfacing circuits ..



i'm still working on the LCD interface with the mcu .. mainly i'm going to wire :

- the "Enable" LCD pin to the pic pin 30 (RD7/PSP7)
- the "Register Select" LCD pin to pic pin 29 (RD6/PSP6)
- the LCD's Data pins (DB0,DB1,DB2, ... DB7) to the pic's (pin 33,pin34,pin35,...pin40) in order (which represent RB0 to RB7)
- and of course Read/Write to the GND & Contrast Adjustment to a Potentiometer

- do you think i should do some changes in any of the circuits ??
- should i add a current limiting resistors or some protection diodes to the ADC0 & ADC1 ?? if so what's the right way to wire the protection diodes into the existing circuit ?

Thank you again for your help ..

[HenrikOlsson]

Hi,
Is the analog input circuitry, ie the sensor and filter etc powered by an external source or does your circuit supply power to it as well? I ask because it would be much easier for you to just simply switch the power to the whole circuit instead of just the microcontroller but I suspect there must be a reason for not doing that?

If you do need to have the analog circuitry powered and just power down the uC (can't think of a good reason for that if the analog circuitry isn't connected to something else as well) then I don't see an easy way to prevent current going into the input and possibly forward bias the the protective diode on the input thus basically supplying the Vdd rail of the uC - except electrically disconnecting (think relay etc) the output of the analog circuitry from the input on the uC. Instead of powering the uC down completetly you could perhaps just pull the MCLR low or put it to sleep.

Again, I'm not saying you WILL have a problem doing it the way you have it but you MIGHT.

The LCD connections sounds allright, just DEFINE them properly in PBP if you're going to use LCDOUT. You could ofcourse use 4-bit mode instead of 8-bit if you're running short on pins.

/Henrik.

[irilias]

Thank you gentlemen for your replies, much appreciated ..

That's the whole thing that i've attached ( Conditioning Circuit "Amplification + Filtration ..." plus the Command Circuit "Motor + electrovalve" .. )
besides the LCD & MMC interfacing circuits ....

i'm still working on the LCD interface with the MCU but mainly i'm going to wire :

- the "Enable" LCD pin to the pic pin 30 (RD7/PSP7)
- the "Register Select" LCD pin to pic pin 29 (RD6/PSP6)
- the LCD's Data pins (DB0,DB1,DB2, ... DB7) to the pic's (pin 33,pin34,pin35,...pin40) in order (which represent RB0 to RB7)
- and of course the Write/Read pin to the GND & the Contrast Adjustment to a Potentiometer .. .

- do you think i should do any changes to any of the circuits ?
- should i add some current limiting resistors and/or protection diodes to ADC0 & ADC1 ? if so, how can i wire the protection diodes the right way into the existing circuit ?

Thank You again for your help ..