p16f84a input signal

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chyun84

New Member

• Nov 29, 2006

• #1

may i know what's the range of voltage for input pulse on porta??
what i mean is, how much voltage needed to on the pic16f84... not the supply voltage... thanks

 

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Pommie

Well-Known Member

Most Helpful Member

• Nov 29, 2006

• #2

See section 9.2 of the datasheet. Datasheets are wonderful things, just so full of data.

Mike.

 

akg

New Member

• Nov 29, 2006

• #3

-0.6 to vdd+0.6 w/o i/p resistor , it is detailed in the data sheet .

 

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chyun84

New Member

• Nov 29, 2006

• #4

what u mean by -06 to vdd+0.6???
i'm currently working on hand clapping projects.. and i get around 0-3V for each claps... so do u think the pic16f84A able to receive the signal in portA as pulses?

 

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eng1

New Member

• Nov 29, 2006

• #5

chyun84 said:

i'm currently working on hand clapping projects.. and i get around 0-3V for each claps... so do u think the pic16f84A able to receive the signal in portA as pulses?

Click to expand...

Yes, it is. The input high voltage on RA0/1/2/3 is 2 V (with Vdd=5 V). But consider if you need some hysteresis...

 

picasm

Member

• Nov 29, 2006

• #6

You could use the RA4 input, it is a Schmitt trigger which helps to filter-out noise in the pulses being detected.

 

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chyun84

New Member

• Nov 29, 2006

• #7

that means my 0-3v is ok and if i use RA4, it will filter out the noise izzit? thanks ^^

 

eblc1388

Active Member

• Nov 29, 2006

• #8

chyun84 said:

that means my 0-3v is ok and if i use RA4, it will filter out the noise izzit? thanks ^^

Click to expand...

You are in for a big surprise.

While RA0 to RA3 works with a min. of 2V for HIGH level, the RA4 input is of a type Schmitt trigger buffer which according to the datasheet requires 0.8*Vdd input to accept as a HIGH level. That's 4V minumum for HIGH at a Vdd of 5V.

 

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ajc

New Member

• Nov 29, 2006

• #9

Hello.....I dont really think you will be very successful using
RA4 to detect positive going input voltages....yes, I agree
with LC...I think you will be surprised.

What I had to do, using RA4 of 16F84
was to use a pullup resistor to set it high
and code it to set it high and read it as
an input to detect Negative going
pulses...you will need an inverter 7404??
to invert your positive input signal.

Believe me, I have gone crazy with RA4,
thats why I have white hair. It will
easily detect positive to negative pulses.
Hope this helps....Art

 

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chyun84

New Member

• Nov 29, 2006

• #10

what u mean is changing my circuit to 'normally on' condition?? but if so, then its quite hard for me to write programming using picbasic pro right?

 

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eng1

New Member

• Nov 30, 2006

• #11

Add an external comparator. I think it's required for yor project.