Please, explain me, your questions are about post #24 or about post #33. I am confused.

Pretty sure he was responding to post #25 by electricspidey, not either of your schematics.

 

Good questions. It vas idea only. Now I finished simulation. Seems R5 = 1.2 k as current limiter is too big - current is 0.7 mA only.
When resistor R5 = 100 Ohm, LED's current is 20 mA.
View attachment 141136

According to the theory that the Vf of LED will be less than Vbr(breakdown), so when they connected with pin to pin and one of the LED is reverse the polarity, so no need two diodes, only need the diodes when the LEDs in series with a current limiting resistor and then in parallel together.

 

Pretty sure he was responding to post #25 by electricspidey, not either of your schematics.

OK. You can see how small LEDs current. And I used in simulation red LEDs. They have forward voltage 2V. How about 3...3.5 V for white LEDs ? I think you need increase voltage for LEDs feeding. Maybe up to 9...12 V.

 

Please, explain me, your questions are about post #24 or about post #33. I am confused.

There was a message replied to -- ElectricSpidey said: ↑
So that wasn't replied to you.
And I mentioned that because the circuit was too simple and could be damage the LEDs, specially when he didn't considering the voltage came from the inputs side.

 

OK. You can see how small LEDs current. And I used in simulation red LEDs. They have forward voltage 2V. How about 3...3.5 V for white LEDs ? I think you need increase voltage for LEDs feeding. Maybe up to 9...12 V.

I just thought about a simple issue, if the inputs current is enough to providing what the LEDs need then probably only need one resistor and two LEDS and it's done, what do you think about this point?

 

According to the theory that the Vf of LED will be less than Vbr(breakdown), so when they connected with pin to pin and one of the LED is reverse the polarity, so no need two diodes, only need the diodes when the LEDs in series with a current limiting resistor and then in parallel together.

You are right. But I follow rule of DickCappels. He said: "Some LEDs cannot tolerate any reverse bias without suffering long term degredation."
https://forum.allaboutcircuits.com/...ifferent-color-leds-with-2-wires-only.143034/

 

I just thought about a simple issue, if the inputs current is enough to providing what the LEDs need then probably only need one resistor and two LEDS and it's done, what do you think about this point?

I do not like it. Because for V forward=3V for white LEDs and V inputs = 3.3 V we need to put resistor R = (Vinp - Vled) / Iled then
R = (3.3 - 3) / 0.02 = 15 Ohm. In this case, if line will suddenly shorted we can have fried logic gates.
And more: I am trying to solve problem in general case. Tomorrow they will need to light 300 mA LEDs and my solution will help them.

 

I do not like it. Because for V forward=3V for white LEDs and V inputs = 3.3 V we need to put resistor R = (Vinp - Vled) / Iled then
R = (3.3 - 3) / 0.02 = 15 Ohm. In this case, if line will suddenly shorted we can have fried logic gates.
And more: I am trying to solve problem in general case. Tomorrow they will need to light 300 mA LEDs and my solution will help them.

What I thought was that if the inputs voltage are 5V, not 3.3V, because I can't setup the input condition, so it just a thought.

 

OK. You can see how small LEDs current. And I used in simulation red LEDs. They have forward voltage 2V. How about 3...3.5 V for white LEDs ? I think you need increase voltage for LEDs feeding. Maybe up to 9...12 V.

I have a 12V source, 3.3V or 5V only refer to the logic of my MCU.

 

The 1k resistor allows a microcontroller signal voltage to manage the PNP just fine.
The design above with a resistor below the bridge screws up signal control of the PNP

 

I have a 12V source, 3.3V or 5V only refer to the logic of my MCU.

Good. Then change R5 in schematic (post 39) to 510 Ohm for 20 mA which is nominal for LEDs 5 mm diameter.

 

If the current from uC are enough for the LEDs, probably this is the easy way to do.

 

I have a 12V source, 3.3V or 5V only refer to the logic of my MCU.

If you can connect directly to IO_A and to IO_B use this schematic:

 

I'm pretty sure he said he wanted to do this on the cheap...so to speak.

"I do want to keep the cost to minimum, so I don't really want to use a h-bridge, relay etc"

The cost of a single relay is dirt cheap.. usually less than $2 and done..
They have spent more time (= money) trying to figure out a way to not just spend the $2..
Makes no sense to me to not do it and be done..

 

The cost of a single relay is dirt cheap.. usually less than $2 and done..
They have spent more time (= money) trying to figure out a way to not just spend the $2..
Makes no sense to me to not do it and be done..

What kind of relay can be working on 100 Hz or even 80 Hz?

 

What kind of relay can be working on 100 Hz or even 80 Hz?

Good point. I had forgotten about that requirement. I was imagining one light at time being on, and I wasn't thinking about pwm or anything like that.

 

Good point. I had forgotten about that requirement. I was imagining one light at time being on, and I wasn't thinking about pwm or anything like that.

If all the conditions and requirement didn't write down on the schematic then we will miss this and miss that ...

 

I do want to keep the cost to minimum, so I don't really want to use a h-bridge,

Is this some kinds of commercial product?
If it is not, why you care so much about the cost since many circuits won't cost much?
How many mA that the uC could provides?
Did you see the posted #52, is it doesn't match your application, why?

 

...why you care so much...?

Let's turn that around. Why do you have more posts on this thread than the OP. Or, why do you care so much?

For him, the advice is free. What motivates him to NOT have us optimize his idea? Nothing.

 

Is this some kinds of commercial product?
If it is not, why you care so much about the cost since many circuits won't cost much?
How many mA that the uC could provides?
Did you see the posted #52, is it doesn't match your application, why?

It’s a prototype at this stage. We are just testing out different part of a design. Could lead to a commercial, I hope.

So the lower the cost, the better.

I totally understand why you suggest the circuit on post #52. In our application, we may need to drive 4 leds instead of 2. (Still two color, but 2 will be in serial). So I may prefer the h-bridge solution.

I can see what your suggested on post #52 is perfect for some other application.

Or maybe it’s the Chinese in me, I always want to do thing cheaper if possible

ps: we haven’t settle on a MCU yet