Alt-BEAM Archive
Message #05117
To: beam@sgiblab.sgi.com
From: Don Papp donp@cronus.oanet.com
Date: Thu, 8 Jul 1999 10:50:39 -0600 (MDT)
Subject: [alt-beam] Power Smart Head
On Thu, 8 Jul 1999 JVernonM@aol.com wrote:
> Just look at the circuits introduced almost daily by Wilf. Consider the Power
> Smart Head. It is a much better approach and it came from the list. People
> are already building the thing (myself included). An actual better circuit,
Out of curiosity, anyone else have trouble getting the FLED to
work with the PSH cct properly? The FLED I have lights up very dimly -
not enough to even see unless the room is dark. I thought perhaps my FLED
had too high of a Vf, but some tinkering and substitution didn't really
help. If you're in the same boat, here's a couple alternatives:
1) Live without a "lock" LED
2) Make a FLED-alike with some extra components
+---/\/\/\---|<|---+ R1
| |
+---/\/\/\---|>|---+ R2 LED
| |\ | Rled / /
+-------| >O------+----|>|----\/\/\/\---|>|------> X
| |/
|+
=== C1
|
|
GND
The inverter is 74HC14 (schmitt trigger inverter)
C1 is 1uF
R1 (on time) is 100k (.1 sec on)
R2 (off time) is 1M (1 sec off)
All Diodes 1N4148 or similar
Rled = 470 Ohm
Ground all unused inputs to the 74HC14 (or it will suck up power
needlessly)
The point marked 'X' (cathode of the LED) would connect to where the
FLED's cathode in the power smart head would normally connect. The 3.3k
resistor in front of the FLED in the original design is ditched.
How it works
------------
The single inverter works as a simple oscillator with adjustable (t=R*C)
times for on and off. It runs all the time, but the LED only lights when
the PSH is locked. (No LED lit = very little power consumed) Also may
even consume LESS power than a FLED, since you can make the LED on time to
be very small (ie just enough to notice it).
Advantages
----------
1) Easily reproduced and stable. The FLED it replaces seemed (to me) to
be an iffy part of the design.
2) Appropriate FLED could be harder to find than the parts for this
replacement
3) Possibly uses less power than a FLED (?)
Disadvantages
-------------
Increases chip count from 1 to 2 (or DOUBLES chip count, depending on
if you're a glass is half full/half empty type of person)
And from that it follows that more components = more complex = harder to
freeform.
I'm interested in hearing if anyone else has had trouble with the lock
FLED on the PSH cct. If so, and there is interest, I can make a schematic
of the alteration and put it on the web.
| Donald Papp, T.T., MCP
| Support Analyst
| OA Internet Inc.
| don@oa.net
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