What's the voltage on output pin when it's HIGH?

**TonyA** · - 23rd April 2008, 00:31

I added "TRISB = 0" and still read approximately 2.5V at portb.7

Thanks,
T

**Ramonetnet** · - 23rd April 2008, 00:33

Then either :

a) your Vdd is 2,5 volts

b) your PIC is gone nuts

c) any other I dont know right now - time to sleep here

Cheers.

**TonyA** · - 23rd April 2008, 00:56

I'm sure that I'm getting 5V to power my PIC.

T

**keithdoxey** · - 23rd April 2008, 08:37

How long is "pausetime"

You are toggling the pin between high and low and your meter will probably not see the voltage stable for long enough to get a true reading.

Currently the pin is operating on a 50% duty cycle and 2.5 volts just happens to be 50% or 5V !!!!

Comment out the "low port b.7" statement which means once the LED comes on it will stay on but you will then have a stable condition on the pin to be able to measure.

My guess is that it will then read 5V

**keithdoxey** · - 23rd April 2008, 08:43

also cant see what the code is meant to achieve because irrespective of whatever value you have for pausetime the led will alsways be at 50% brightness as the on and off times are the same.

If you are trying to get a variable brightness then with pausetime being 0-255 you should have something like

Code:

main:

adcin 0, timeVar

pauseTime = timeVar / 12

high portb.7

pause pauseTime

low portb.7

pause (255-pauseTime)

goto main

which will give a total time of 255 but the on will vary from 0-255 whilst off will also change from 255-0

**TonyA** · - 23rd April 2008, 15:06

Yes, you're right. The on-off time is too fast for the meter to register.

I am just trying to achieve a TTL pulsing; 5V, 0V, on/off at different rates. The LED was put in there just for a visual reference, it's not part of my finished circuit.

The purpose of this pulsing of the pic pin is to replace a Schmitt Trigger Pulse Oscillator.

It is working the way I expected "in circuit", but I was just wondering why I couldn't read discreet 5V and 0V on my meter, (taking reading on the bare pin, not resistor or LED).

If I had an Oscilloscope I guess I would see the TTL (I would see the square wave pulse).

I'm starting to see the benefits of an Oscilloscope...

Thanks for all the help, I appreciate it very much.

T

**sayzer** · - 23rd April 2008, 08:42

Originally Posted by TonyA

I'm sure that I'm getting 5V to power my PIC.

T

Depends on where you are measuring your Voltage at.

A - B, A - C , B - C ?

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