Buffer-amplifier chip?

Archiver

Hello all,
I'm trying to interface a PIC with the parallel port on my
computer and I'm only getting ~3.5v for a 'high'. Can anyone suggest a
buffer-amplifier chip that will take a flaky logic level and turn it into 5v?

Thanks, Duncan

Archiver

At 01:42 PM 4/18/00 -0400, orthner@s... promulgated:
>
>Hello all,
> I'm trying to interface a PIC with the parallel port on my
>computer and I'm only getting ~3.5v for a 'high'. Can anyone suggest a
>buffer-amplifier chip that will take a flaky logic level and turn it into 5v?
>
>Thanks, Duncan
>
Duncan -

Is this a laptop ?

Bruce

>
>
>

Archiver

Hi all,

I don't really have a solution for this, for which I'm sorry Duncan, but I have
a
similar problem with my bs2sx: the pins will only output a tiny 0.5 volts when I
set them high ...

I have been trying rctime in the standard light sensor setup from the manual on
all the pins individually and that works perfectly. But when i write a program
that sequentially sets all pins high for a while and measure the pins directly
with a volt meter I only get 0.5 volts.

For every pin there is a 220 ohm resistor on my board ( I soldered those in
after
I saw it on a picture earlier and since allmost all setups require resistors
between the pin and the external circuitry I thought it would be handy to put
them in as standard ) Maybe I shouldn't have done that?

kind regards,

Sandor

orthner@s... wrote:

> Hello all,
> I'm trying to interface a PIC with the parallel port on my
> computer and I'm only getting ~3.5v for a 'high'. Can anyone suggest a
> buffer-amplifier chip that will take a flaky logic level and turn it into 5v?
>
> Thanks, Duncan

Archiver

Sandor Rabe <sandor.rabe@e...> writes:

>when i write a program
>that sequentially sets all pins high for a while and measure the pins
directly
>with a volt meter I only get 0.5 volts.
>
>For every pin there is a 220 ohm resistor on my board (

Are these 220 ohm resistors going from your output pins to ground? If so,
5000/220 = 22 milliamps, which sounds like too much current to source,
especially if you have several pins set to Hi at the same time. Just an
idea...

Also, a common "cure" is to use "Schmidt triggers" on your outputs
(74xxx14) to get a full TTL Hi.

Steve

---

Steve Roberts: sroberts@s...

---

Archiver

You can use a 74125 which is a 3.0 logic to 5 volt logic buffer.
However a 3.5 level is "OK" for TTL.
Kent Dillin

Archiver

Thanks everyone for ideas on this. I ended up using a '244 buffer-driver
and it worked great. Really cleaned up those flaky signals coming from the
parallel port...

Duncan

Archiver

Hi Steve

>
> >when i write a program
> >that sequentially sets all pins high for a while and measure the pins
> directly
> >with a volt meter I only get 0.5 volts.
> >
> >For every pin there is a 220 ohm resistor on my board (
>
> Are these 220 ohm resistors going from your output pins to ground? If so,
> 5000/220 = 22 milliamps, which sounds like too much current to source,
> especially if you have several pins set to Hi at the same time. Just an
> idea...

Nah. I've connected resistors to pin0..pin15 and beyond the resistors there
is just a bank of "sockets" in which I can plug wires going to whatever
external circuitry. The resistors are only there to protect my pins. Also, I
tested them sequentially which means the there's only 1 pin high at a give
time. I measured the potential between the pin after the resistor and ground
with a volt meter and that read 0.5 volts. I din't hook up anything else on
those pins when measuring.
[noparse][[/noparse]....]