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24V into pic pin is ok (PIC12F629)?

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treez

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Hello,

We have a circuit in which 24V will be connected to a PIC pin, but there will be a 100K resistor in series with the pin. Will this be OK?
Here is the basics of the circuit...showing the pin with the 100K attached to it.

https://i47.tinypic.com/n3t5pk.jpg


(Doing it like this saves us a lot of circuitry)

By the way, we already do this but with 12V, and we've had no problems....will it be ok with 24V?
 

I think you need to ask Microchip this question. Personally, I'd say DON"T DO IT. True, the resistor limits the current, but 24 volts is 24 volts.
 
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I have asked on the microchip forum...but yet no answer......i asked in "digital IO ports" section.

I find answers are not always forthcoming on microchip forum website......and theyre sales reps never get back, since i do not have a big big organisation behind me.


Well, this works with 12V......so why not 24V?....how far above 12V is the limit, in your opinion/
 

treez said:
Well, this works with 12V......so why not 24V?....how far above 12V is the limit, in your opinion
Click to expand...

There are several appnotes discussing the application of AC power main voltage levels to an I/O pin of a PIC.

Example:

Interfacing to AC Power Lines

While I would NOT recommend such an approach for several reasons, the lack of isolation and the probable future law suites come to mind, it is doable.

The above appnote should give you some insight as to the I/O pin construction and design limitations for your particular DC application.


BigDog
 

I would send a tech support request right to Microchip rather than the forum. They are generally pretty good at getting back, even to us little guys.
 

Thanks guru, but that is only PIC16C5X devices....i am wondering about PIC12F629
 

You can even connect the said PIC micro to 220 volts AC. But a resistor is needed in series to protect the port. Any voltage avove 5 volts is hazardous to the device. In case of AC light dimmers with PIC12F629, we use a 2.2M resistor to a pin which monitors the zero crossing.
Cheers
 
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treez said:
but that is only PIC16C5X devices....i am wondering about PIC12F629
Click to expand...

As Pranam77 pointed out the appnote applies to the PIC12F and PIC16F series as well.

BigDog
 
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Yaa I agree with Pranam77 as even I also connected 440v 3 phase supply to the PIC Pins through 10Mega Ohm resistors for one of my project.....Only one need to make sure that the pins that you connects such a high voltage need to have diode protection enabled on it....there are some pins on the PIC family don't have this diode protection on it to please check that....the link that bigdog mentioned to you will give you idea how it works....

Good Luck

Milind
 
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