Hi,
It's been a while since i left but i got a small electronics problem and cant solve it..
Problem: I have a signal wire that is always set to HIGH (+5V) except when a switch is hit and it goes to LOW (mass) for the exact time the switch is pressed. Unfortunately i need sort of a delay for this circuit - so when the switch is hit the signal should stay low for a definable time. I could use an Arduino for this easily but would like to keep it simple as possible since the whole system consits of like 40 wires and gets extended all the time - and building an arduino for every 8 or so lines is not really my goal.. so i went for basic electronics.
I have a 555 as monostable circuit (see attachment) that works (also added a signal inverter on the Output). but only if i have signal as well as ground and VCC. This would be a good solution but i would like to fit it more to the environment of only having one wire to play with.
Has anyone here any idea how to add a delay to just one wire thats constantly HIGH except for when a switch is pressed? My best guess would be to add capacitors to act like sort of battery.. but i have no idea if thats possible at all.
So.. ideas?
As you haven't said what period you want you will have to play about with the R & C connected to pins 6 & 7
Try this:-
Monostable.pdf (16 KB)
Thanks for the idea Grumpy_Mike.
Thing just is the main idea is the following:
I have one signal wire which is HIGH all the time except when the switch is hit - it pulls it to LOW for an instant, afterwards it goes to HIGH again.
Now what i want to do is to put "some electronics" on that single wire that will lengthen the time the signal is LOW for a certain time (if possible definable by a poti).
I think that the 555 is less and less useful for me since it needs VCC and GND as well.. i thought about using a resistor, poti and capacitor.. but really cant get it to work 
I have one signal wire which is HIGH all the time except when the switch is hit - it pulls it to LOW for an instant, afterwards it goes to HIGH again.
Yes and for that you need a monostable. You can use a 555 or a 74LS121 or 74LS123.
I think that the 555 is less and less useful for me since it needs VCC and GND as well.
I don't know what you mean, it seems an odd thing to say.
i thought about using a resistor, poti and capacitor.. but really cant get it to work
No it won't work with just passive components.
You still haven't specified any times so it is hard to say if this delay has to be pico seconds or mega fortnights.
"mega fortnights" sound like a useful unit for that awkward bit between pre history and geological time..... 
I once worked it out to be just under 500 centuries I think. I used it in my astronomy lectures for a bit of a joke.
Interestingly enough, W|A will actually take mega fortnight as an input.
But back on topic, anything you use is going to have to have to have Vcc and Ground. If you get one of the CMOS 555s it will use less power, but wouldn't it be much less trouble to just use those extra wires to connect to Vcc(since either way, you'll have to connect both to a common GND) and not have to recharge and replace large capacitors. And getting a whole bunch of >1F capacitors won't be cheap. Plus, as the capacitor's voltage drops, so will the "HIGH" voltage from it. Eventually it will be LOW all the time from the Arduino's perspective.
I just woke up and I feel like I've typed something wrong, but I can't tell.
Edit: link fail
Grumpy_Mike:
Yes and for that you need a monostable. You can use a 555 or a 74LS121 or 74LS123.
...
I don't know what you mean, it seems an odd thing to say.
I thought i need a dedicated power and gnd line for the 555 that is indipendent from the trigger line?
Grumpy_Mike:
No it won't work with just passive components.
You still haven't specified any times so it is hard to say if this delay has to be pico seconds or mega fortnights.
The delay should be between "instant" (as input) up to a few seconds (5 or 10).. so nothing big.. Basically i can do this with a 555 - but dont understand to wire it up to just be driven on one wire
like:
switch ----------- "555 assembly" --------- sensor
Singnal from switch to 555 is like -------_------------
and should look like on the sensor -------________---
And currently i can wire up a 555 to do that, but the main problem right now is that i need VIN and CTL to be wired to some power and gnd wires..
So.. basically.. can you hint me how i have to wire up the 555 to just use the trigger line to work?
Man i am so far out of electronics that i dont even know anymore how to phrase questions and descriptions. I just hope it is somewhat understandable..
edit currently i use Circuit Simulator Applet
but dont understand to wire it up to just be driven on one wire
You can't.
You need power, ground, input trigger and output.
No way round that.