negative pulse I/O pin how to?

[rickyD]

Hi guys
I want to set one of the pins on my pic chip to
pulse a negative pulse.
I have this 7 color leds with a microchip inside.
There are 3 leads on the led anode cathode and a
trigger for the chip. The trigger is a negative trip.

I looked in my picbasic book but I dont seem to
fine a command that lets you do this.
Is it possible?
And how is it done?
Any help is much appreciated.
Thanks

[Jerson]

Ricky

Please explain what do you mean by negative pulse. Negative logic? or Negative voltage pulse with respect to common ground. Negative logic is easy to do. Just do this
Low PulseOutputPin
High PulseOutputPin

[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!