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From: "Tom Faloon"
Subject: Re: How do I feed 0v/1v logic levels to CMOS?
Date: Sat, 12 Oct 2002 15:54:01 +0100
NNTP-Posting-Date: Sat, 12 Oct 2002 14:48:37 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
There are many ways you could do this, and an OP Amp comparator is certainly
one of them.
A transistor level shifter would be even simpler, (3 components) but it will
invert the signal.
To do that, connect an NPN transistor as follows.
Connect emitter to ground. 10K resistor from collector to 12V. Collector to
the CMOS input. Another 10K resistor from the base to the output of your
The base resistor may seem very small. That is because the drive voltage is
very low. It has been chosen using the following assumptions. - High o/p
from temp monitoring device is at least 1 Volt, when battery is near
exhausted. Transistor used has minimum HFE of 40. This circuit should work
with just about any NPN transistor.
To answer this properly really needs a little more information.
Worst case voltages and current drive capability of monitoring device
If you are going to use the CMOS signal to clock anything, the signal may
need to be debounced!
Hope this helps.
Miles wrote in message
> Can anyone please help me with (I hope) a simple problem.
> I have a temperature monitoring device with 1.5v battery supply. It
> logic levels of 0v (low) and 1.5v (high).
> I want to connect this to a CMOS circuit I'm constructing running of
> supply (on a PC). The CMOS circuit is a simple logic one using 4001 type
> transistors etc.
> I know I need some kind of voltage shifter to up the high level to at
> or so. I'm considering using single-supply op-amp as a voltage comparator.
> Can anyone suggest a simple way of doing this? Any help, references,
> would be very much appreciated.
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