Acquiring digital inputs

Your signal range is not so great that you can't use a fixed input range of +/-10V with a programmable threshhold comparator. In logic state acquisition speed is usually much more important than level resolution, ditch the multiplexer. The 16-input circuit is only four quads. It would be simpler to use a common threshold, use a comparator designed for bipolar supply, and a type with 3.3V TTL output. These drive a latch or register clocked by your external trigger, which is also appropriately converted to TTL.

one way to get that wide input range is to slap an opto-isolator diode across it and drive a CMOS input from the transistor. We can do 5V to

40V that way,m and polarity becomes irrelevant.

David

Could you be more clear please?

Thanks Marco

just use your signal to drive the diode of an opto-isolator. the range of permissible currents can be large, which means a wide range of voltages can drive it.

Use the output transistor with as large a load resistor as you can tolerate, and put that into a CMOS input.

Oh, and close the box, because it will then trigger on stray daylight!

David

Ok,

Thank you very much! Marco

Thank you very much? It is unheard of to use optocoupler diode loading as a digital logic probe for several good practical reasons. And there "ain't" no way you're going make a variable threshold. Be suspicious of vulgarisms such as "slap" as in "slap an opto-isolator diode across it"- this usually means an untrained practitioner.

Mhhh... I'm confused...

If I use a comparator I also need to connect a switchable input, in case of the 1 corresponds to 5v, 10v, 15v.

Instead the use of a diode could avoid this trouble.

What do you suggest?

Many Thanks Marco

what is the purpose of the schmitt trigger?

it'll not be much use there.

nowhere have you stated what you want to use as a threshold voltage if +3V is acceptable in all cases an optoisolator with resistor suited to a

3-10V signal would do the trick, put a small-signal diode antiparallel to proctect the opto from reverse bias.

if you use an optoisolator on each imput it'll protect your setup from electrical faults,

it may be possible to matrix the optos output ends thus saving you on parts to do that... you'd need a circuit to select each row and possibly a buffer on each column unless you arrange it such that the column output is compatible with your 3.3v system.

If you don't need isolation on the inputs there's probably a better way.

Bye. Jasen

My suggestion is that I can design a circuit which will consider 0V to be a 0, and anything from 4 to 30V a 1.

That sounds like a solution to the problem as described.

Using an AC optocoupler I could make it accept -4 to -30 OR +4 to +30 as a 1

If you like it, use it. If not, do something more complex.

David