Activating on/off switch via detecting 12vdc presence

Thread Starter

izon

Joined Mar 17, 2013
217
I need a circuit that will turn on or off (change state) a switch when the presence
of a 12volt DC source is detected. (It would work similar to being able to turn on your modern TV
via supplying AC from your switched wall outlet..) Let me know if I'm not making myself clear.
Of course, the simplest and least expensive method would be best.
Thanks for your help.
 

Alec_t

Joined Sep 17, 2013
14,280
In that case an NPN transistor, for example, could be the switch, with the 12V source connected to its base via a suitable resistor (e.g. 10kΩ).
 

Thread Starter

izon

Joined Mar 17, 2013
217
Good suggestion.... as I go I probably think of more details... guess I would like the
12vdc isolated from the "load".
I'm pretty low on the knowledge so a schematic and possible parts to use would be
helpful as well. Thanks!
 

Thread Starter

izon

Joined Mar 17, 2013
217
Sorry... I'm pretty bad at explaining things and not even sure how I will eventually put this idea to use...
But going back to the idea of how this would apply to a TV set. If it is on a switched AC outlet and you
turn on the AC via a room light switch, the TV will not come on as it would have on an old school
mechanical switch on the TV.

So what I think I need is to have something that would "get around" the need to also press the
power on button on the TV even though AC has been applied via the outlet.

When the wall switch is turned off, the set goes off, and to repeat the process requires the power
button to be pressed again after the AC wall switch has been turned on. So let's just "substitute
the 12vdc in place of the 110AC in the scenario and accomplish the goal of pressing the power button (once the
12vdc has been applied) without actually having to press the button.... geeesh bet that's confusing
 

Reloadron

Joined Jan 15, 2015
7,501
To a point what you are describing is a SSR (Solid State Relay) or for that matter even just a plain relay. You have a low DC voltage we can call the Control voltage which in turn can turn On or Off a higher voltage source for example 120 VAC. Really depends on the Voltage and Current we want to switch. The problem is using the TV for an example anything to do what you are looking to do would be unique to the actual device be it a TV , Stereo or other electrical/electronic device. We would need to look at the power On/Off by device, know how it works and then develop a means where it would resume following power loss.

Using a home computer as an example a computer PSU (Power Supply Unit) has 5 Volt SB (Stand By) power which is always on. Momentarily pressing the power button places a momentary Logic Low on the PS_ON# pin starting the PSU. If power is lost the start button must be pressed again. However, I could use a One Shot multivibrator so when power is restored my circuit will automatically provide a logic low to the PS_ON# pin on the motherboard bridging the button. This would be unique to the system. Anyway, doing what you want to do would be figured out on a case by case basis.

Ron
 

Thread Starter

izon

Joined Mar 17, 2013
217
Thanks to both of you fellows.... very well explained. Sorry to be rather vague as to my application as I am not totally sure
about how the "push button" functions in the circuit.
I will have to postpone this until I know more and I understand how there needs to be more detail on what is going on.
Thanks for now... may revisit this question later on..Best regards to all.!
 

Colin55

Joined Aug 27, 2015
519
"So what I think I need is to have something that would "get around" the need to also press the
power on button on the TV"

Build yourself a robot with intelligence. When it detects that you want the TV turned ON, it will get up from its chair, walk over to the TV and press the ON button.
 
Top