input voltage more than Vdd

[skyrock]

Hello,

I was wondering if this would work if my Vdd for the PIC is 3.3v, then I connect a 5v input without any voltage divider into the input pin. Will this work?

Regards,
SKY

 

[skyrock]

Hello,

I was wondering if this would work if my Vdd for the PIC is 3.3v, then I connect a 5v input without any voltage divider into the input pin. Will this work?

Regards,
SKY

 

[Pommie]

No, you need to put a largish resistor in series with the pin otherwise the PIC will get powered from the signal via the protection diodes.

Mike.

 

[Pommie]

No, you need to put a largish resistor in series with the pin otherwise the PIC will get powered from the signal via the protection diodes.

Mike.

 

[blueroomelectronics]

Most 3.3V PICs have 5V tolerant input pins on digital only inputs (no AN on those pins) Check the datasheet in the electrical characteristics section.

 

[picbits]

Déja Vu !!!

 

[Pommie]

Arrrrrrgghh, I'm going mad.

Mike.

 

[skyrock]

Most 3.3V PICs have 5V tolerant input pins on digital only inputs (no AN on those pins) Check the datasheet in the electrical characteristics section.

The PIC i'm using is a 3-5v PIC, i.e. 16F628. But I connect it's input pin to another PIC's pin which take an input of 5v.

So, Mike is saying that the first PIC will take power from my input instead? What is largish resistor? sorry, i'm pretty new to this thing.

SKY

 

[Pommie]

Yes, your second pic will get powered from your first pic if you just connect them together. Use a 10k resistor between them and you should be fine.

Actually, your 3.3V PIC could end up running at 4.3V without the resistor.

Mike.

 

[skyrock]

Thanks everyone, i'll go try out my circuit then.

anyway, I was trying to use PIC_A to capture PIC_B's output and show the result on LCD. I intend to use this as a scope to capture what actually does PIC_B is sending out. Any suggestion?

I've figured to use 16f628 for PIC_A running @ 20mhz, and PIC_B @ 4mhz. Then i'll just capture whatever the state is for the output port on B when either of them changes. This is to make something like a signal capture for PIC_B

 

[aamirkhan]

u can use an optocoupler

 

[ArtemisGoldfish]

You could always throw a diode in series to get a decent 1.5v drop.

 

[picbits]

You could always throw a diode in series to get a decent 1.5v drop.

1 diode will only give around 0.7 volts drop - you need 2 diodes and you'll get around 1.4v drop

 

[Pommie]

1 diode will only give around 0.7 volts drop - you need 2 diodes and you'll get around 1.4v drop

I think he was referring to my post and the series diode would feed the protection diode and therefore power the second pic at 3.5V.

Mike.

 

[skyrock]

alright, i'm getting confused. Now I'm trying to build a circuit with PIC16f628 at 5v and connect to an LCD display from NOKIA 3310 which maximum input is 3.3v.

so, I connect the PIC and LCD thru portB 0-4 (5 pins), my question is, should I put Diodes in between the LCD and PIC pins, or use a voltage divider? or just put a 10k resistor? (PIC running at 5v, LCD max input = 3.3v)

SKY

p.s. forget about the PIC connect PIC scenario. I've already build a logic analyzer for that case.