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Is there an "auto-detect" tri-state buffer?

R

Rich Grise

Jan 1, 1970
0
http://www.delorie.com/house/furnace/zone1.html

I've had a lot of problems with people linking images from my server
into their web pages and eating up my bandwidth. You're likely using
web-based mail, which looks just like that case. I try to detect
those and block them, to save my bandwidth. I just put in a gmail
exception, that seems to be the common case, please try again.

If you have CGI capability, you could block out access from everything
except your own server, with a little clever scripting.

Good Luck!
Rich
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
Rich said:
It's doable, but probably WAY more work than just tracking down and
extending the enable signal from the driving part.

Difficult, huh. How about two transistors and four resistors?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
D

DJ Delorie

Jan 1, 1970
0
Rich Grise said:
If you have CGI capability, you could block out access from
everything except your own server, with a little clever scripting.

That's similar to what I do, but I do occasionally put up temporary
photos for people to see - which breaks if you use webmail or webnews.
 
J

Jasen Betts

Jan 1, 1970
0
Hi All,

I'm wondering if there is such a thing as a tri-state buffer that can
auto-detect the driven signal? It would recognize a driven high or low and
output the same, and be able to detect a floating input, and go to high Z.

I want a buffer that can source or sink >50mA, something my PIC won't
do. The auto detect saves me driving a separate enable line.

Can anyone point me to such a thing?

autodetect is tricky.
maybe do this:

--+-- VCC
/
|/ C
-----| NPN
| |\|
| --\
pic ---+-[1K]--+---
| |/
| |/-
`----| PNP
|\
\
----+-- GND
 
J

Jasen Betts

Jan 1, 1970
0
I don' think the original poster was after that, more he wanted to use
the pin bidirectionally
One I can recall is some TI op-amps, where a single pin sets one of
three bias levels TLC271? I've seen others as well.

relatively easy to do in analogue

+V
|
[R3]
|
in --[R1]--+--- Vout
|
[R2]
|
-V

another chip that used tristate inputs is the MC145026/145028
encoder/decoder pair historically used for garage door remotes
etc.
 
J

James Arthur

Jan 1, 1970
0
Jim said:
Hi All,

I'm wondering if there is such a thing as a tri-state buffer that can
auto-detect the driven signal? It would recognize a driven high or low and
output the same, and be able to detect a floating input, and go to high Z.

I want a buffer that can source or sink >50mA, something my PIC won't
do. The auto detect saves me driving a separate enable line.

Can anyone point me to such a thing?
autodetect is tricky.
maybe do this:

--+-- VCC
/
|/ C
-----| NPN
| |\|
| --\
pic ---+-[1K]--+---
| |/
| |/-
`----| PNP
|\
\
----+-- GND

That doesn't go rail-to-rail, which might bother some logic buses.

...Jim Thompson

Actually it does, via the 1k. Slow tail at the end, and all
that that implies, yadda yadda yadda.

Cheers,
James Arthur
 
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