Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 2 down vote favorite

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:

this

with a timed "push event"

share|improve this question
Can you be more specific about the thing ? – Rocketmagnet Apr 24 '12 at 19:02
1  
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
1  
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

3 Answers

up vote 2 down vote accepted

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:

enter image description here

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...

share|improve this answer
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
up vote -1 down vote

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.

share|improve this answer
Or a whole PC :-) – Telaclavo Apr 24 '12 at 19:12
2  
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
2  
@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
show 1 more comment
up vote -1 down vote

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

share|improve this answer
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

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.