Hi,
We used to have a saying back in the 1980's:
"The hardest thing to do in electronics is to get a bulb to light up".
The reason for this is because it always seems so simple that we often overlook things that could go wrong.
This however is about lighting two LED's. Unfortunately, there are a limited number of parts available which i'll list here.
1. Bi color LED, one internal LED is blue 3.0v, one is green 2.5v, common cathode, so they are both in same package, and the package has three leads: one lead is CC, one is Blue anode, one is Green anode. (Also see side note far below).
2. Any number of 1N4007 diodes, but use the least number of diodes possible.
3. Any number of 82k, 1/2 watt resistors, but use the least number possible.
The application is as follows:
1. The LED will be used as an indicator for a power strip. The power strip has a single SPST switch on it that powers the six outlets when it is turned on, and does not power them when it is off. The power strip may be used with small wall warts or even a 500 watt appliance.
2. The 'blue' part of the LED is used to show that the power strip is plugged into the wall only.
3. The 'green' part of the LED is used to show that the switch is turned 'on' only.
So in a typical day of use it may goes as follows...
The strip is plugged in, the blue LED lights up because the switch is off, and nothing is plugged into the outlets yet. Later, something is plugged in, and then the switch is turned on, and then the green LED lights up.
Still later yet, the switch is turned off and the blue LED lights up again.
So the operation is fairly simple, but the part types are limited as above. The idea is to use as few parts of those above as possible.
There is a small side note about the bi color LED. If the blue LED is wired directly in parallel to the green LED (ie both anodes connected together) only the green LED will light up because it hogs all the current because the voltage is lower than the blue LED voltage, and is it low enough to really get all or most of the current.
This is actually something i may want to use myself too, not just an interesting problem.
We used to have a saying back in the 1980's:
"The hardest thing to do in electronics is to get a bulb to light up".
The reason for this is because it always seems so simple that we often overlook things that could go wrong.
This however is about lighting two LED's. Unfortunately, there are a limited number of parts available which i'll list here.
1. Bi color LED, one internal LED is blue 3.0v, one is green 2.5v, common cathode, so they are both in same package, and the package has three leads: one lead is CC, one is Blue anode, one is Green anode. (Also see side note far below).
2. Any number of 1N4007 diodes, but use the least number of diodes possible.
3. Any number of 82k, 1/2 watt resistors, but use the least number possible.
The application is as follows:
1. The LED will be used as an indicator for a power strip. The power strip has a single SPST switch on it that powers the six outlets when it is turned on, and does not power them when it is off. The power strip may be used with small wall warts or even a 500 watt appliance.
2. The 'blue' part of the LED is used to show that the power strip is plugged into the wall only.
3. The 'green' part of the LED is used to show that the switch is turned 'on' only.
So in a typical day of use it may goes as follows...
The strip is plugged in, the blue LED lights up because the switch is off, and nothing is plugged into the outlets yet. Later, something is plugged in, and then the switch is turned on, and then the green LED lights up.
Still later yet, the switch is turned off and the blue LED lights up again.
So the operation is fairly simple, but the part types are limited as above. The idea is to use as few parts of those above as possible.
There is a small side note about the bi color LED. If the blue LED is wired directly in parallel to the green LED (ie both anodes connected together) only the green LED will light up because it hogs all the current because the voltage is lower than the blue LED voltage, and is it low enough to really get all or most of the current.
This is actually something i may want to use myself too, not just an interesting problem.
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