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!

[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

[rickyD]

Ok I got the led from radio shack.
Its brand new 7 colors.

The led has 3 leads coming from it.

One is the cathode or negative.

One is the anode or positive.

There is a third pin and this pin is the trigger
for the microchip in the LED.

The trigger is tripped with a ground or negative charge.

This LED is so new mouser and digi key dont have it.
There is no data sheet and you have to get it for your self.

So there is no way to set a pin to ground and then set it to nutral?
Not + and not - neg.

I use a 16f84a for most projects but I have some 18f2620 that I like.
Some help with pin info would help or where to get it from.

Like the pins have a lot of different uses RC6/TX/CK

Pin address/?/?
What do these mean?
Or where can I get the info
on what these mean?
Just here for fun and I dont want to make waves.
Just trying to keep my old mind sharp.
Thanks for any input you may have.

[mackrackit]

Here is the data sheet for the LED.
http://www.alldatasheet.com/datasheet-pdf/pdf/184695/MICRO-ELECTRONICS/MSGBB557TA.html

You do not need a negative voltage. 0 volts is what you need. Ground is not negative.
Reread the post from skimask.

RC6 = PORTC.6
Have you looked at the data sheet for the PIC you are planning to use? It explains the functions.

From the data sheet.
TX = Asynchronous serial transmit data output (EUSART module); takes
priority over port data. User must configure as output.

CX =Synchronous serial clock output (EUSART module); takes priority
over port data.
Synchronous serial clock input (EUSART module).

[rickyD]

Thanks guys!
I found the data sheet for the pic18f2620 witch I like.
The only problem is its 300+pages.

I tryed to print the book but I ran out of ink.
So I'm reading cpu.

I really just want to say thank you for all the help.
I have dun this before start at the bottom and work up.
And I know after you master a program you get tired of
the dumb questions.

Im self tot on 3d studio max a 3d grafix program.
And lodes of grafix programs for making textures.
I use to make tracks that you could race a car on with a game
called re-volt.
I make like 3 pages of tracks for this game and had a great time.

But I found pics and a new interest in electronics and
programing.
SO here I am.
I will be asking lots of kinda dumb questions in the time to come.
Thanks you guys!
Rick