Working (don't mind my lack of protoboard skills - it's midnight)

But.... I just read this on another forum:

"You should never put LEDs directly on logic signals. They have a lot of capacitance and will make your logic signals very ugly. If you ever get a chance to look at it on a scope you will see what I mean."

 

See
View attachment 138285

This design would give me the third state.

 

But.... I just read this on another forum:

"You should never put LEDs directly on logic signals. They have a lot of capacitance and will make your logic signals very ugly. If you ever get a chance to look at it on a scope you will see what I mean."

Are you driving them at MHz or just low frequency switching (few few khz or less).

 

They are just for on/off control panel indication. They might change state once every 5mins !

 

They are just for on/off control panel indication. They might change state once every 5mins !

Capacitance will not be an issue for your project.

 

Capacitance will not be an issue for your project.

Thanks !

 

I'm sure 10mA - 15mA would be fine.

Since the LEDs are merely indicators, I'm sure you could use a lot lower current (5mA?) unless you'v got some really naff LEDs.

 

Since the LEDs are merely indicators, I'm sure you could use a lot lower current (5mA?) unless you'v got some really naff LEDs.

Agree - I just need to get the actual LED's I'm going to use and then do some testing.

 

Better schematic (I used KiCad this time):

 

You will only need D1 and D2 so you can have R1 and R2 different values. Otherwise only one resistor is needed and the diodes can be removed.
And I think a pullup may be better than a pull down. Some bus expanders have pullups included so if you have a pullup and pull down the result may be more undefined. Still, whatever works

 

You will only need D1 and D2 so you can have R1 and R2 different values. Otherwise only one resistor is needed and the diodes can be removed.
And I think a pullup may be better than a pull down. Some bus expanders have pullups included so if you have a pullup and pull down the result may be more undefined. Still, whatever works

In the schematic I made both resistors the same value but until I have the actual LED I am going to use I can't decide on the values.

I have to find light pipes first then I can choose an LED.

 

Some bus expanders have pullups included so if you have a pullup and pull down the result may be more undefined. Still, whatever works

I am thinking about just using the 74HC595 shift registers instead of bus expanders for ease of use. Haven't decided yet.

 

For original poster an for future reference, here is a solution that I had made after searching the interenet for a similar issue.
I have attached the PDF of a charging circuit, and here is a short video I made about it:

So in short, you can drive two leds with one pin.
In my case, I used a single inverter, in your case, you can use a 74ls04 hex inverter. You may need a few of them though

I know it is a very late reply, but might as well be added for prosperity.