negative pulse I/O pin how to?

[rickyD]

Hi Jerson
I want the pin to go from no volts to be a negative.
And back to no volts.
I can make them pos.+ no problem HIGH and LOW.
Just dont know how to make it negative.
Thanks

[skimask]

A cap on the output, charge it up, then dump the charge. You'll get a negative spike, but that's about it.
If you read the datasheet for your particular PIC, you'll see under the 'Absolute Maximum Ratings' that negative voltages ( Vss - .3v depending on your PIC ) can damage your device.
Simple way - Charge pump - ICL7660/ICL7662 - using a pin on the PIC and a transistor or MOSFET to control that output.

[rickyD]

Hi Skimask
Your way ahead of me.
So I can use a cap. and charge it with a + voltage
and use the -neg. to trigger the led?
I think thats what your saying.

Im a newbe and dont understand the transistors I
know thay up the +volts from a pic chip pin.
I see now I need to look in to changing + V to -V.
I dont know how to do this.
O boy did I take a big byte this time.
HELP!

[rickyD]

I just did some reading and I see that transistors work on the
-neg. side I thank.
This is good to know. See I dont know to much yet.
Thanks for the input it helps.

Ill have some more dumb Qs soon.

Im a hobby electronic guy I just found the pic chip and what
you can do with it a short time ago. It is so cool what you can do.

And its not that much cash to get going.
I did hand over the $250.00 for the full picbasic pro ver.
That was a pane in the paycheck but I like it.
So Im hooked on this stuff for now.
Thank you guys!

[mackrackit]

Do you have a dual power supply set up for this project? Do not know what you are up to, but might make things easier for you to get the negative you want.

[skimask]

Don't really understand why you need a negative trigger in the first place....mainly because you haven't given us any information on the 'chip' that you're using. Might just be reading the datasheet wrong.

Unless you're confusing 'negative' with 'ground', sort of the way a lot of people think a 12v car battery has a +12v and a -12v, when in reality, it's +12v and common (or if you want the other way, common and -12v). LEDs, or circuits for that matter, don't GENERALLY require a positive and negative voltage, they need a voltage differential. Doesn't matter if you've got +5v/common (0v) or 105v/100v, both of them have a 5v differential.

[Acetronics2]

Hi, Ricky

I already see some smoke from my location ...

you'd better tell us what reference is your LED ( or where it comes from: link , please ! ).

negative triggering means triggering with a +5v - 0 v - 5v pulse ...

... my two cents.



Alain