LED 101 - light when a plug is inserted
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Posted by anonymous on October 7, 2004, 10:40 pm
Please log in for more thread options 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? | |||||||||||||
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Posted by anonymous on October 7, 2004, 11:07 pm
Please log in for more thread options 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? | |||||||||||||
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Posted by John Fields on October 7, 2004, 7:17 pm
Please log in for more thread options wrote:
>(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? --- Put an LED in series with a 470 ohm resistor across the load, with the anode of the LED pointing toward +9V. -- John Fields | |||||||||||||
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Posted by anonymous on October 8, 2004, 7:00 am
Please log in for more thread options
>>am I thinking on the right track?
>
> --- > Put an LED in series with a 470 ohm resistor across the load, with the > anode of the LED pointing toward +9V. > > -- > John Fields 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. | |||||||||||||
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Posted by Randy Day on October 8, 2004, 3:05 am
Please log in for more thread options anonymous wrote:
>>>am I thinking on the right track?
>>
>>--- >>Put an LED in series with a 470 ohm resistor across the load, with the >>anode of the LED pointing toward +9V. >> >>-- >>John Fields >
> > 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) - 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 www.tech-chat.de) | |||||||||||||
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>
> 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?
>