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timer circuit theory help

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warzo69

New Member
I have a need to build a timer circuit that is adjustable, I have always wanted to learn more about circuitry and feel this is a good project for me to learn with. I am not asking anyone to post a schematic for, as I would like to learn how to assemble and design the circuit myself. I understand very basic components and am a very fast learner. The ultimate goal of this circuit is to control a water pump in a water display in my pond. What I need to learn is how to vary seconds minutes hours on/off. I did some research and found a few schematics for timers that use 555 and 556 chip's but no sites that really explain the theory.

My wife told me I need to find a hobby and when I looked back at the things that I wished I'd learned, basic circuitry was at the top of my list.
 

BrownOut

Banned
This sounds like an excellent way to start with electronics. I suggest you start with THIS TURTORIAL It's the best one I've found on the web. Study a few of the schematics, and ask any questions you have in this forum. You'll also need some basic transistor thoery, because the timer most likely won't drive your water valve by itself, and you'll end up connecting a power BJT or FET. Good luck.

PS: also found these TRANSISTOR TURTORIALS on Tony Van Roon's website.
 
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MikeMl

Well-Known Member
Most Helpful Member
Looks like Tony's web pages are no longer available at the Univerisity...
 

BrownOut

Banned
Nope. He retired in August. I've had the devil of a time trying to find them. Finally, I found the notice that his site moved. Fortunately, the site is still available in it's entirty.
 
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warzo69

New Member
so basically what im reading is that a simple timer can be made from a 555ic a resistor and a capacitor. The duration of the pulse is controlled by the capacitor and resistor ratings. I know I may be getting ahead of myself here(I usually do), but does anyone have a link that would show me how to read and display the numeric value of the pulse on an lcd or small LED display.
 

BrownOut

Banned
Best to beg, borrow or steal an oscilloscope if you want to know the pulse width. A 'scope is the most useful instrument on any electronics bench.
 

ericgibbs

Well-Known Member
Most Helpful Member
so basically what im reading is that a simple timer can be made from a 555ic a resistor and a capacitor. The duration of the pulse is controlled by the capacitor and resistor ratings. I know I may be getting ahead of myself here(I usually do), but does anyone have a link that would show me how to read and display the numeric value of the pulse on an lcd or small LED display.

Thats a fairly big step.:)

You could calibrate a potentiometer and dial to enable easier setting of the ranges.

Why do want to display the period.?
 

BrownOut

Banned
Also, you can simulate your circuit in LTSpice ( free software ) The package include the 555 timer in its library, and has a graphical display you can use to view the output pulse. There is lots of support available on this site for this package.
 

warzo69

New Member
basically my goal is to create a timer with variable cap's/resistor's and display the math as I change the values of the components so my wife can alter the water display without a calculator or me for that matter! Again this is about me learning first and less things for her to complain about second!
 

ericgibbs

Well-Known Member
Most Helpful Member
basically my goal is to create a timer with variable cap's/resistor's and display the math as I change the values of the components so my wife can alter the water display without a calculator or me for that matter! Again this is about me learning first and less things for her to complain about second!

I would opt for a 10 turn pot and counter dial.

Using the 555 formula for your required time periods with a fixed cap and 10 turn pot would be accurate enough.

As your electronics experience is a little rusty, making a timer period display would be difficult.
 

warzo69

New Member
Your idea is only a few minutes old, and already suffers from "feature creep."

I understand, however I am an aggressive learner and my ability to stay focused requires an increasing level of difficulty. With the help that everyone has provided so far I will have this circuit designed by this evening and will be looking for the next addition to my skill-set.

Thanks you again for everyone's help and support!
 

ericgibbs

Well-Known Member
Most Helpful Member
I understand, however I am an aggressive learner and my ability to stay focused requires an increasing level of difficulty. With the help that everyone has provided so far I will have this circuit designed by this evening and will be looking for the next addition to my skill-set.

Thanks you again for everyone's help and support!

hi,
When you have finished the circuit, post it.;)

If possible use a CMOS version of the 555 timer.
 

warzo69

New Member
hi,
When you have finished the circuit, post it.;)

If possible use a CMOS version of the 555 timer.

I fully intend to, I was hoping to get criticism on what I may be able to make it a cleaner circuit. i know my first timer will probably be a little clumsy but so far everyone here has been great and I hope to continue to benefit from everyone's knowledge here.
 

KMoffett

Well-Known Member
....What I need to learn is how to vary seconds minutes hours on/off. ...
One thing to understand from the beginning concerning 555 timing is that they will not work well for long periods like many 10's of minutes to hours. There are other ways to do that, but playing with 555's is a great way to start, and may be sufficient for pump on-times.

Ken
 

warzo69

New Member
For my first attempt I am aiming for a 5 minute on and 15 minute off cycle. However in the future I would like to create one that I can vary over a 24hr period. How would you suggest that I do this?
 

ericgibbs

Well-Known Member
Most Helpful Member
For my first attempt I am aiming for a 5 minute on and 15 minute off cycle. However in the future I would like to create one that I can vary over a 24hr period. How would you suggest that I do this?

hi,
If you can get these ic's they make very long timers.
 

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BrownOut

Banned
I had an idea about how to make a digital readout very easily for a timer project. It will not be challenging enough for the O/P, but I decided to post it for us mortals. Let's say the equation for pulse width is .693*R*C. So, use a 100K resistor and 144 uF capacitor ( not a typical value, use a 100uF and 47uF.... close enough) For the resistor, use a 100K, dual ganged, and connect the "other" resistor to 10V. Then, go to Harbor Freight Tools ( or some other Cinese product distributor ) and buy a cheap, $5 DMM. Wire the DMM to the wiper of the resistor you connected to 10V. Read out the timer value (seconds) in volts.

Edit: Changed my values.
 
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