Would be possible to scale this to work with higher supply voltages, let's say between 15 and 35V?
I tried to do it but Q3 in this circuit needs a 5V supply otherwise it doesn't turn off.

This will work from 15v to 35v but you'll have to change the current limiting resistors for the desired LED current.

 

This will work from 15v to 35v

Possible. My understanding is the green LED is switched from a 5 volt source but the supply for the red LED is anything between 15 and 35 volts.

 

Speculation, speculation, speculation. Currently on post 42 and the OP hasn't been here since post #9.

 

Well that doesn't mean the TS is no longer interested. Besides there is no harm in discussing alternatives.

 

Possible. My understanding is the green LED is switched from a 5 volt source but the supply for the red LED is anything between 15 and 35 volts.

not specified. But easily modified...

 

Everything still looks very complicated to me.
Using only three components in addition to the LED and working on a 35V supply with a 17V threshold.

Another neat trick is to add a capacitor. That makes a circuit that can detect short pulses that exceed the threshold, by making the green LED stay on longer.

 

What does that mean or imply?

"External Logic" means that for one LED to totally switch off and another totally switch on there must be more than that scheme in post #38. That circuit will provide a dimming of the red LEDand a brightening of the green LED.

 

i like to keep it simple, this is simple and scaleable voltage wise. The red LED will be dimmer than the green due to the voltage drops of the 2 diodes. May be possible to delete one of the diodes, depending on the forward voltage drop of the Green LED.

 

i like to keep it simple, this is simple and scaleable voltage wise. The red LED will be dimmer than the green due to the voltage drops of the 2 diodes. May be possible to delete one of the diodes, depending on the forward voltage drop of the Green LED.View attachment 225606

Still not as simple as mine! (Post #46)

 

That circuit will provide a dimming of the red LED and a brightening of the green LED.

Not true.
The TS requirements from post #1:
When an external positive voltage is applied (for example 5V), the red led switches off and the green led illuminates.
for example: initial state: external voltage 0V -> red led on, green led off
external voltage changes to +5V -> red led goes off, green led turns on
if the external voltage changes back to zero it resets the leds to the initial state.

Post #6 : The leds consume about 20 mA which the transistors like a 2N5550 can easily supply.

And post #9: Would be possible to scale this to work with higher supply voltages, let's say between 15 and 35V?
The only issue is if the 5 volt external voltage can supply the 23ma required in my design.

 

Still not as simple as mine! (Post #46)

If V2 is only 5 volts how is that going to work

 

If V2 is only 5 volts how is that going to work

As in post #10

 

Have fun arguing the points y'all. I've made my contributions and I'm not going to sit here waiting for Christmas. OK, Christmas is only three days away - but the point is that there are different solutions possible. Personally I don't care if the TS chooses MY suggestion(s) or someone else's suggestion(s). If they've gotten the answer they wanted and have now left - that's their choice. I make mine. I'm done here.

 

As in post #10

Still don't see it.
From post #10. If "in" is 5 volts how does that turn off the red LED?

 

See attached:
V2 = input. V1 = 5V supply.

 

See attached:
V2 = input. V1 = 5V supply.

I tested your circuit. If V2 = 5 v both LEDs are on. LED1 only shuts off when V2 is above 6 volts

 

Why is this so hard. Top pair of PNPs and two resistors limit current to 16mA (5v supply) to 18mA (50v supply). Bottom pair of transistors alternate the red and green LEDs at 16 or 18mA (depending on supply voltage).

 

Why is this so hard.

Who ever said anything about 100mhz signal to switch LEDs ? With that circuit both LEDs are visually both on.

 

Who ever said anything about 100mhz signal to switch LEDs ? With that circuit both LEDs are visually both on.

Your eyes respond very slowly. Note the Lower case "m" in milli-Hz. That is, 10 second cycle (5-second green, 5-second red). It is just an easy way to simulate a 5v signal being applied and 0V applied.

 

Note the Lower case "m" in milli-Hz.

I know that.