Tristated output to two common Base transistor issue

[Bruce]

Hi Russ,

(Did you set that up on a simulator?)

Yes. I ran it through Electronics Workbench. I would just go with some Alegro LED drivers,
but it does work if you have the board space.

[Luciano]

Hi,

This is the circuit posted by Bruce.

This version was tested on a breadboard with a microcontroller.
On the picture you can see the values of the resistors and the
type of transistors I have used.

Datasheet of the transistor BC558 (PNP)
http://www.fairchildsemi.com/ds/BC/BC558.pdf



Best regards,

Luciano

[flotulopex]

I think I now understand clearly the difference between an electrician (me) and you clever engineers

There's only one word to say: BRAVO!

... et merci 1000 fois.

NB: somebody talked about a "simulator". Is it really possible to simulate an electronic circuit that matches reality? Also with PICs?

[sayzer]

Ok; I removed my post.

[Bruce]

Nice work on testing/verifying all the various circuits Luciano.

I vote we keep this thread alive. I can't help but think there's
a better way to do this with fewer discreet components, and
even less quiescent current drain.

Seeing all the various circuit ideas is very interesting.

Maybe we should create a new topic category named Tips &
Tricks for hardware/software solutions similar to the Microchip
web forum & Tips & Tricks app-notes?

These spark a lot of interesting ideas/approaches to doing things.

[Acetronics2]

Hi, Folks

From the brainBoard ...

Et c'est la France qui repasse en tète ...

"The fingers in the nose" ... as we say here ...

Alain

PS : Tested ans Verified ... with 20 mA per Led ...

[RussMartin]

Bravo, Alain!

If you haven't seen it, here is Alain's tested circuit:

<IMG SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2007&stc=1&d=118952080 6">

(His PDF file is easier to read.)

The input is at 2.75 VDC, eliminating the worry about a floating input pin when the input is set to high-Z.

I think I mentioned the possibility of using MOSFETs several posts back. I was going to try it with Luciano's original circuit, something like this:

<IMG SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2008&stc=1&d=118952090 8">

Exchanging the positions of R6 with D1 and R5 with D2 in Alain's version will accomplish the same result, but without the voltage divider.