Re: About some parts on logical circuits

That would be correct as long as every input is accounted for. Older
TTL circuits would predictably float high, but that's not always the
case for CMOS. So an unconnected input to a CMOS chip should be tied
to the appropriate logic level.

My first PCB for the project took that in account though it doesn't show on
the schematic.

I didn't see the resistors that you were referring to. Was this by any
chance on some pushbutton switch logic? Often you will see a cap and
resistor in a debounce circuit.

Precisely, I wasn't aware of the pull-down resistor issue. They're the ones
I was thinking about.

The transistor part brings no interrogation (maybe it should...).

If you want to take a look at the schematic, here it is :
http://dr.gang.free.fr/test/Swtiching.pdf

The ICs are dual JK flip flops and a quad OR gates. The schematic shows
JFET
transistors but I'll use more common NPN ones.

There's a difference in the way that a bipolar loads the JK's output
pin as compared to a FET, but you probably won't have any problems.

That's something I can't figure out : what is the load seen by the JK's
output ? Since each transistor will have to feed a dozen of LEDs at 40mA
each, that makes a rather high current and I'm wondering if this won't suck
too much from the JK's output which will "see" the LED network through the
transistor's gate.
In the same idea, in a cascade of triode, what is the current going from the
first tube plate to the next's grid ? For me, a grid is a dead-end which
therefore can't draw current. I'm probably not seeing things the right way
but can't figure it out.

I suggest that you change a couple things on your schematics: Don't
bother snaking the +5 or ground lines around. They clutter the
drawing. Use a small filled-in up-arrow for +. Use a larger hollow
triangle pointing down for ground (like Fender schematics). Draw those
right at the chips or wherever. Actually you don't have to draw any
power connects to the chips if you're posting something for us. People
know they're powered.

Actually, this schematics comes from Multisim that I use for simulating
circuits. It's simply a PDF print.

And change to individually drawn FF's and gates. Rather than drawing
the package outline, draw the bullet-shaped logic symbols for AND/OR
and individual boxes for the FFs. It makes your intent more clear.

Indeed the circuit is messy if you stick your head in it for the first time.
Luckily enough, there are competent people in this NG. :)

Speaking of intent, what are you going for here?

I'm making a 3 channel amp. The switching scheme involves optocouplers. Each
channel has its own network of 5 to 8 optocouplers to turn on (while the
others would turn off) when switching to it. This schematics is the
footswitch pedal that'll allow me to change channels. There are mechanical
systems to switch between 2 channels but I've never seen anything fit for a
3 channel switch so I went logical.

Thanks for your answers/comments.


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