Rotary Switch to Variable Timing Circuit?

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• 03-15-2011, 09:21 AM
sdashiki
Rotary Switch to Variable Timing Circuit?
I need some EE help with a project I am trying.

What I need is a timing chip whose time(s) are set by rotating a dial.

Set the dial to 1sec. When you power the circuit (switch) you get a 1sec pulse of power to the output and then it stops.

Im looking to have a 10-12 position rotary dial connected to a timing chip. How the hell do I go about even starting this project? How does one get EXACT timed pulses from the chip...do I need to program it?

I need non-crazy times like 1s, 1/100th, 1/1000th etc.

So, to reiterate my ranting unintelligible self:

set dial to a certain time
power on the circuit
timing chip reads setting on dial and outputs appropriate amount of time in a power pulse

This will allow me to turn on/off a device with perfect timing I can set.

HELP!? Are there things already set up like this? Do I need to get a programmable chip and dev board?
• 03-15-2011, 05:17 PM
OldSpark
It all depends on the accuracy & delays you need.
A 555 timer is analog and uses resistor-capacitor combinations for fractions of a second to many 10's of minutes.

Otherwise there are programmable timers - check Jaycar.

Then there's the FB, Arduino, etc.
• 03-15-2011, 10:28 PM
sdashiki
Yes, the 555 Ive researched quite a bit. But, unfortunately if it requires different sets of res/cap for each setting on the rotary dial, it defeats the purpose of my project. Itll be too large for the small containing space.

I was hoping for a rotary dial which sends different "signals" for each different setting. Hexadecimal seems the only way to accomplish this because the 555 is the only other way, and using a normal switch between res/cap banks, isnt gonna cut it. A chip would read the "signal", i.e. setting, and output a pulse of power for a specific length of time.

Using a dev board, unless it lets me take some chip off and install it as I just described...will again be too big and much overkill.
• 03-15-2011, 10:44 PM
OldSpark
I reckon forget the coded switch.
It's the timer that will do the decoding (as per normal practice (for single-users)).

Maybe consider a digital up/down rotary instead (1+3 wire) so you don't need 1+12 inputs (or 1+4 bits) etc.
• 03-16-2011, 10:44 AM
sdashiki
I believe this is going to call for a programmable microcontroller I can feed input from a switch and output timed pulses...but what chip, how to program, who knows!!!?
• 03-16-2011, 10:47 AM
malcom2073
Well you could go with Arduino, they're cheap, and if you know C, you know how to program one. They're fairly easy
• 03-16-2011, 11:17 AM
OldSpark
That was gonna be my recommendation.
Cheap, and with common open source information.

But I prefer uPCs over PICs anyhow....

(And I still prefer assembler LOL!)
• 03-16-2011, 11:22 AM
sdashiki
But a dev board is gonna be too big. I need, literally, like a 555 chip thats not analog but programmable.
• 03-16-2011, 11:35 AM
OldSpark
Fine.
Build your own PIC (8 pin)
Or use a Stamp uPC.

There are digital chips that can count down from a binary value. But then you have the problem of providing the binary value....
You can use ordinary rotary switches with enough diodes - but do you really want that?
Hence a PIC to do the binary, in which case it may as well do the timing - ie, the lot.
• 03-16-2011, 01:13 PM
sdashiki
So, I can have a rotary switch, hexadecimal, which feeds values to a PIC and the PIC then pulses for a set period, sending power to another circuit for that period.

Dont suppose youve got a direction I could be looking for parts and a programmer?

The resistor bank with a ordinary switch has been tried, and while I am currently working on it to get it small and into the compact space where this goes, I wanted something less analog.
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