Put an LED in series with a 470 ohm resistor across the load, with the
anode of the LED pointing toward +9V.
LED 101 - light when a plug is inserted
Oct 08, 2004
8 Replies
Here's what Im hoping to accomplish:
I have a +9V lead and a ground going to a plug. I want to light the LED when the plug is inserted. The load on the plug will vary from 0 to ~100 mA.
Is this (relatively) straightforward or am I thinking foolishly?
(d'oh)
my first thought was to run a line parallel to the 9V connected to the (+) plug lead with a 350Ohm resistor. I don't think this would work as all the current would go through the open line. What if I put a 90K resistor on the open line? Seems like this would give me ~100mA to my plug and ~20mA to my LED...
am I thinking on the right track?
What John means is put the LED in parallel with the circuit being powered; am I correct in assuming you want an LED mounted, say, in the *outlet* - that lights when something is plugged into it?
If you have a spare connection on the plug and socket you plan to use, you can do it simply:
Socket Plug | | +V-------| ---|------o------ +V to circuit | | | o----------| ---|------o | | | | -V-----o-| ---|------------- -V to circuit | | | | |-----| | .-. | R | | | | | | '-' | | | | | LED V | - | | | ---- (created by AACircuit v1.28 beta 10/06/04
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I must be too ignorant to understand your explanation properly. It sounds like this would always be on regardless of the state of the plug (putting the LED + resistor across the load) -
On further consideration I think I have a problem in that the current draw for each possible output device is unknown and variable. I can't rely on
100mA of current being pulled through the circuit. Some of these devices only need 5-10mA. This would give me LEDs of variable brightness. Based on my naive understanding it almost sounds like I need a digital circuit that would "pull high" when any current flows through the line and then all the way off when current stops.
[snip]
Can you arrange it so a small SPST switch gets pressed when you plug something in?
Socket or "module" Plug .------. .-----. | | | |
+V-o-------- | ------------- | | | | | o--|--o| | | | | |==== | | o--|--o| | | | | | | | |-V---------- | ------------- || '------' '-----' || || R || ___ ||-|___|- | | | V LED | - | | ---------- (created by AACircuit v1.28 beta 10/06/04
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Can you create a small module to plug in between the present socket and plug to do this?
If you're looking for something to sense a voltage drop or current surge when a load is plugged in, you're looking for something quite complex and likely to be unreliable.
I assumed (silly me...) that the load was in the device into which the
plug would be inserted. However, it now seems like the load is going
to be portable and connected across the plug.
Probably the easiest/cheapest way to do what you want to do would be
to put a small resistor in series with the return to -V then use a
voltage comparator to sense the drop and turn on the LED.
I can't change the wiring of the plugged in device. It would simply complete the connection from +9 to ground with a varying load / current draw.
Ack. Ok. Ill put this one down.
TY for the input.
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