Tristated output to two common Base transistor issue

[Luciano]

Hi Bruce,

Here are the results:


When Tab is open the whole circuit uses 1mA.
I have used 3 transistors BC558.

Thank you!

Best regards,

Luciano

P.S.

Do not connect LEDs in parallel like that with just one series resistor!
If you need to connect LEDs in parallel, use one resistor for each LED.

This was just a quick test to see if 50mA were available.

[RussMartin]

What a coincidence, Bruce! --Last night, I started sketching something that came out kind of similar to your approach, except I was using NPNs. Yours is better. (Did you set that up on a simulator?)

And, Darrel, I think I was going in your direction. This was to be my next step:

<IMG SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1997&stc=1&d=118933392 4">

. . . with D1 and D2 generic small-signal or switching diodes (e.g., 1N914). I had long-forgotten about using a zener diode in that manner!

[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.

[Luciano]

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.

Hi Russ,

This is not possible because on the original board made by Roger,
the anode of one LED is connected to the cathode of the other LED.

The purpose of the voltage divider was to keep the board as it is.
(The voltage divider can be made by adding one wire to the board).



Best regards,

Luciano

[Acetronics2]

This is not possible because on the original board made by Roger,
the anode of one LED is connected to the cathode of the other LED.

Luciano

Hi, Luciano

In your great science, do you have an answer for that :

" But why does always Roger make boards before thinking to how they should work ...??? "

Will "Swiss precision" only be a legend ???

LOL ...


Hi, Roger ...

Try to tell us about your Projects BEFORE heating the soldering Iron ...

... so much time saved !!!

Just Jokin' ...

Best Regards

Alain

[Luciano]

" But why does always Roger make boards before thinking to how they should work ...??? "
Will "Swiss precision" only be a legend ???
LOL ...

Hi Alain,

He must be a musician! Did and redo...Didgeridoo. (Note the assonance).

* * *

See this document about the three input pin variations of a 16F87x:
http://www.basicmicro.com/downloads/...h_halfChp4.pdf

Best regards,

Luciano

[flotulopex]

As said, the first board I made was fitted with standard leds (picture in post #12).

But, following a good old swiss habit, I observe and think how to make things even better... and get into trouble.

Frankly, I thought this kind of question would have been common, maybe even boring.

A few days ago, I made a second prototype where I used my SMD NPN's and paired the leds. The visual effect is quite good (will make a video).

Now, if I have to make a third board with MOSFETs, this won't be so terrible (the iron is still hot).

And, please remember Leonardo Da VINCI: he invented so many things but built so few. I try to balance and do the opposite

Many many thanks to all.

NB: "Swiss precision" is not a legend and if you have a closer look to a chocolate bar, you'll notice that even the hazel nuts are lined-up! And yes, I'm a musician.

[sayzer]

Hey Roger,

I am getting a lot of good stuff via this post and all is free.

But, going back to your original issue, I was wondering why don't you consider using something like 74HC164 ? You can use three or four I/O pins and control cascaded 74HC164 ICs for 20 LEDs.

You can set all 20 LEDs with uS of times at once.

-------------------------------------

[flotulopex]

As you can see the image in my post#12, the led's PCB is quite small (narrow). It is ment to be put inside an existing stop-light case ("boîtier" in french).

I haven't enough space to put either the µc nor the power regulator on the led's PCB; this is why I made a second PCB for the "power & µc section". It is located outside the stop-light (still inside the car but not inside the case).

Finally, and this is why this all is about, I wanted to reduce the amount of wires between those two PCBs.

Voilà.

Another general info: I made my second proto with 15° leds; this viewing angle is to small, 24° must be better.