# Substitute a button for a timed event?

Disclaimer: I am a total newbie

I have something I bought that once is switched on does something each time I press a button, now, I want that to happen periodically(no accuracy needed) so I was thinking on substituting that button for something.

Is there any simple thing I could put there which would give me a periodic "button press"? Doesn't need to be accurate and I would be thinking on ranges from 5 secs to 30 secs, but anything is acceptable really, I would prefer non-ic alternatives.

Basically I want to swap something like this:

with a timed "push event"

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Can you be more specific about the thing ? –  Rocketmagnet Apr 24 '12 at 19:02
You will need to give us a lot more details. Is this button NO or NC? What voltages are used on it, is there a pull up/down resistor? Why no ICs? I think you are still very much in the brainstorming stage and haven't done enough research on your own to create a good question. –  Kellenjb Apr 24 '12 at 20:16
Kellenjb, I have no idea yet what the voltage is and not sure how to find NO/NC, I will try to extract that info from the device I have. –  Arkaitz Jimenez Apr 24 '12 at 20:54
I vote for the mechanical approach: a motor geared down with a cam attached to the shaft that pushes your button every time it makes a full rotation. –  Faken Apr 25 '12 at 1:12

What's wrong with ICs now??

Anyway, what you want is a astable multivibrator, which is often made with an LM555 (IC!), but you can also make it with a pair of discrete transistors:

The period T = time the button is pressed (t1) + time between button presses (t2), where

t1 = 0.69 $\times$ C1 $\times$ R3, and
t2 = 0.69 $\times$ C2 $\times$ R2

Use the output to drive a reed relay via another transistor. Place contacts of the reed relay parallel to your button. If a contact resistance of a few tens of ohms is OK (the reed relay will be milli-ohms) you can use a 74HC4066 as the switch. But then we're again using an IC...

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what did u use to draw that? looks cool –  Arkaitz Jimenez Apr 25 '12 at 15:42
@ArkaitzJimenez: found it here. Excellent site, by the way. –  Federico Russo Apr 25 '12 at 15:45

A microcontroller or FPGA could do this trivially. You would just need to put a loop counter and raise/lower the output at the desired times.

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Or a whole PC :-) –  Telaclavo Apr 24 '12 at 19:12
Or a servant :-( –  Rocketmagnet Apr 24 '12 at 20:50
Why the down vote? He wants something automatic to simulate pressing a button and either of these could. –  Brian Carlton Apr 24 '12 at 22:37
I didn't downvote. –  Telaclavo Apr 24 '12 at 23:22
@Brian: I didn't downvote, though I don't think it's a good answer. You should give more details of how you solve this using a microcontroller. –  Federico Russo Apr 25 '12 at 15:09
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Sounds a little like a time delay relay. They come with lots of different options, but here's an example:

http://www.smarthome.com/7279/Delay-Timer-Relay-ELK-960/p.aspx

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Can you give some more details in your answer? As it is now you are just recommending a consumer product where as you should be answering an actual electrical engineering question. That product is a circuit board and all, but it is specially designed to be used in smarthome applications which I consider to be consumer electronics –  Kellenjb Apr 24 '12 at 20:10
Still needs a pushbutton, and only gives 1 pulse, not something periodical. –  Federico Russo Apr 25 '12 at 14:47