555 Monostable question

[theangrytomato]

Hi, I am trying to build a circuit that when a voltage is present on a line in one circuit it will momentarily trigger a switch (essentially push and release a button) on another circuit. I tried setting up a monostable 555 circuit, but if the trigger switch isnt released, the light I am using to simulate the relay that will be used to "push" the button just stays on indefinitely. I guess what I am trying to do is instead of using a momentary push-on to trigger the timer, I want to use a SPST relay but still have the output from the timer be a pulse and not just stay on. Is this possible? If this made no sense please let me know. Thanks!

 

[BrownOut]

Sounds possible. Why not post your circuit so we can see what you're doing?

 

[carbonzit]

The simplest pulse generator I can think of is a capacitor in series with the first circuit (the one you want to set the whole thing off). When power is applied, it will generate an exponentially-decaying pulse. Of course, you need to discharge the capacitor to prepare it for the next cycle; this can be done just with a bleeder resistor (a high resistance to drain of the charge gradually), depending on cycle time.

 

[theangrytomato]

Here is what I am trying to do, except the way it's set up the relay on the circuit furthest right would just stay on indefinitely and not momentarily like I want it to. Ignore the math on the top left, the voltages are arbitrary right now, and I haven't worked out exact timing yet so theres no values for the resistors or capacitors, but this shouldn't really matter at this stage. Thanks for the help.

**broken link removed**

 

[ericgibbs]

hi,
AC couple the 555 Trigger input, see modified circuit.

What is the specification of the relay coil.???