🚀 go-pugleaf

In sci.electronics.design Ian Stirling <root@mauve.demon.co.uk> wrote:
> In sci.electronics.design Werner <Werner@nospam.com> wrote:
>> Hi fellow electronics enthusiasts,
>> 
>> I'm trying to build a on/off detection circuit, which is able to check if
>> the connected LCD monitor TV is in standby mode (31 mAmps/12 volts) or
>> active mode (725 mAmps/12 volts). I have put a 0.3 Ohm resistance in series
>> with the 12 Volts DC power supply, so I have a small voltage drop across my
>> 0.3 Ohm resistance, maybe enough to measure this drop using an LM311
>> comparator IC.
> 
> There should be no problem with oscillation.
> Add a bypass capacitor across the resistor to cut down on any problems.
> 
> A simple 100 ohm/1.2K divider between 12V and 0V, and the comparator connected
> to the TV end of the 0.3 ohm resistor.

As others have pointed out, I'm wrong.
Somehow I managed to misremember that the comparator in question works down
to the negative rail, not up to the positive one.

If the monitor takes a composite or UHF input, you might consider moving
the resistor to the negative rail (and dropping it's value to 0.01 ohms or
so) and using the comparator across that).

When bypassed with a capacitor, you won't notice any difference.
(you need to check for any ground connections other than power on the monitor)

-- 
http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
---------------------------+-------------------------+--------------------------
All I want is a warm bed, a kind word and unlimited power -- Ashleigh Brilliant.