Question about connecting toghether 2 output pins on a 08M

[Andres Rodriguez]

I need to send output from two different pins to the same pin on a ULN2003 (see schematic). It will be Out 0 and Out 2 of a 08M. It will never be both at the same time. Which pin sends the output is determined by the position of a switch. I wonder what will happen to Out 0 when Out 2 is high (or vice versa)
I will include the following in the program:
dirs=%00010111

 

[eclectic]

Use a diode in each output line?

e

 

[Andres Rodriguez]

Thank you E,
I'm sure that it will work with the diodes, however. The problem is that the circuit will go in a radio controlled airplane and I have very limited space for the PCB. That is why I was wandering if I could get by without the diodes.
Andres

 

[MartinM57]

These small enough?
http://uk.farnell.com/multicomp/es1a/diode-ultra-fast-1a-50v/dp/1625028

Not sure why you want to do what you want, but:
- can't you do it in the software?
- why can't you put Out0 and Out2 from the 08M's into two different ULN inputs and attach the load (a LED?) to both of the open collector outputs - that will give you automatic OR'ing for free...
EDIT:e.g.
U1 Out0 -> ULN 1B
U1 Out2 -> ULN 2B
J3 pin 1 -> ULN 1C
J3 pin 1 -> ULN 2C
etc

 

[Andrew Cowan]

A SMD 1N4148 is pretty tiny...

Are you sure you cannot do the needed coding in software, rather than needing two outputs?

A

 

[eclectic]

And for more space-saving, the SMD ULN2003

http://uk.farnell.com/texas-instruments/uln2003aid/transistor-array-ic/dp/1543239

e

 

[MPep]

Not sure if this will work, but lets give it a go.

Why not have O0 and O2 go to an individual ULN2003 input. (Total of 6 inputs as opposed to the now 3 inputs). Then common each pair on the outputs. As the ULN2003 only drives low, can't see a reason why it wouldn't work.

Note: I have not tried this.


Just read that MartinM57 has the same idea.

 

[Andres Rodriguez]

Thank all af you

Thank you gentlemen for all the ideas. I tested on a breadboard the idea of using diodes and it worked. Also, Martin's suggestion worked fine. However, the sofware approach will save even more PCB realestate, I'm working on that approach now. Once I did that I'll make the final decision.
Thank you again