Hi
I want to make an electronic timer that will sound an alarm like for in the kitchen, i want it to run off 9V and range from 1min - 30min if possible. have a Pot for ajusting it and a start push button, thanks

Chris

 

Here is a circuit:

http://www.eleinmec.com/article.asp?4

Replace R with a variable resistor and you will be able to vary the time cycle.

 

Hello,

One practicle tip: the resistor may not be larger than 15 MOhms.
See this page for more info:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

Greetings,
Bertus

 

Good point Bertus.

 

hey thanks guys finally i find what i wnated, so if i replace the resistor with a 10M pot how will i know what time it is on do i set it wait and mark it?, and another thing what value shoud the capacitor, im thinking 1000uf

 

You need to calibrate it. Use something erasable at first, set it then see how long it goes for a random setting (or space them out regularly). You can extrapolate the settings after several points.

Or you can use a DVM to set the resistor for a specific time setting, and put a mark there.

Did you read this?

555 Monostable