Hello Friends,
Since this is my first post; I should introduce myself. My name is Jeffrey and I live in Houston, Texas. My college degrees are in marketing, M Business Administration and M International Business. I wish I had taken engineering, because I am fascinated, curious, excited and frustrated, but determined to learn, understand and create. I have spent countless hours reading All About Circuits and the forums, Wikipedia Electronics and a vast number of hyper-links across the industry to datasheets, tutorials, etc. I am willing to spend my time studying/learning, seeking and researching so that I can make something with my own hands. I don't want someone else to do the work for me, but I realize that at some point it is time to ask for help. I have done the necessary footwork (mouse clicking) so that I can ask the right questions and understand the answers.
Borrowing the Sir Isaac Newton quote: "If I have seen further, it is by standing on the shoulders of giants". I need some help from the giants here.

Goal: Create IC that will switch on motor for 20 seconds (Distance*time) once every 24, 36, 48 or 72 hours (Cycle Time).
I discovered the 555 chip timer at my local electronics shop as part of a kit from Ramsey electronics ($10) that comes with a PCB and the basic resistors, capacitors and pot to make a timer with an output. I got a relay to start the 12v motor with the output of the kit. The next requirement is to trigger the timer (Dt) on a desired cycle time (24, 36, 48 or 72 hours).
The 555 kit is inexpensive, so I plan to purchase another for CT. However, I am in development and open to suggestions. That said, how do I trigger timer Dt with timer CT? So that timer CT provides the pulse required to trigger Dt and then restart CT timing period for the next cycle?
I have created and attached a labeled circuit diagram that is modified from the original diagram that came with the kit. The Philips Electronics Data sheet mentions a method called AC Coupling and shows a diagram that involves two inputs: one 10k resistor and a .001uF with another 10k resistor. I have drawn a copy of their diagram next to the Dt trigger.

 

Hello Friends,

Another possible option, but a temporary one, is using my patio lights programmable timer (PTimer) as my Cycle Timer (CT) with a 12V adaptor. (My wife is going to ask what happened to the timer) Problem with that is, PTimer will provide voltage for one minute, which is longer that the 20 second event that is being triggered. How do I stop the current after supplying the pulse trigger to Dt?

 

http://www.zen22142.zen.co.uk/Circuits/Timing/ivt.htm

The time range posibilities goes out to 32 hours, but could probably be stretched to 72.

How accurate does your timer have to be? Like a clock? Or can it be off a few minutes or an hour over 4 days?

Ken

 

Hello Ken,

Thanks for the reply. It can be accurate to within +/- 30 minutes or an hour at 72 hours, without any problem. Accuracy not critical for the cycle timer.

Jeffrey

 

For accurate 72 Hour timing, nothing beats a 32.768KHz crystal with CD4060(s).

 

L.C.,
But, he's going to need another 4060 and a whole bunch of AND gates to decode exactly 24, 36, 48, and 72 hour outputs.

Jeffery,
Is this timer going to be triggered be an event and run one cycle-time and then stop? Or stop and wait for another trigger? Or, continually repeat-cycle at the set time? I wasn't too clear on that.

Ken

 

L.C.,
But, he's going to need another 4060 and a whole bunch of AND gates to decode exactly 24, 36, 48, and 72 hour outputs.

This is what I'm thinking about.

Arrange another 4060 to produce a 12-hr pulse and feed it to a 4017. Combine the various 4017 outputs to trigger a 20 second 555 monostable.

 

My thought now is: the output of a new plug-in 24 hr wall timer with trips at 12 and 24, converted to DC to trigger a 20sec monostable, that clocks a 4017. The selected outputs of the 4017, if AND'ed with the monostable output, would provide 20 sec pulses at 12, 24, 36, and 72 hours with the accuracy of a standard clock.

Ken

 

Hi KMoffett,

Your idea using of a 24-hr standard mechanical clock timer to generate the 12-hr signal is more elegant and simpler than mine.

One can simply use either a AC relay with mains rated coil voltage or an opto-coupler to interface the 12-hr signal to clock the 4017.

 

Hello KMoffett,

The Event is a one shot, 20 second drive DC12v motor stop. I have a 555 timer kit and a relay to run the motor for 20 seconds. Cool thing about the kit is the R3 Potentiometer which has a wheel to select between 100 to 250k ohms, so I can adjust if 20 seconds is too much or not enough.

I want the Event to happen once a day or every other day, or once every three days. So, the cycle is going to be at least 24 hours, would like to select between 24 and 72 hours. I need a 3 second or so pulse trigger for the 20 second event.

 

Ken,

I have a very cool, digital programmable timer that will do the cycle timing. It is 120AC 60 meant for timing the patio lights. The shortest on/off time is one minute, which is problematic for triggering a 20 second event. How could I stop the input from this after 3 seconds? Or, since I have one minute of power, can I set up a resistor/capacitor to pulse trigger after 50 seconds? (providing the final 10 seconds of power to trigger 555 timer)

The very cool timer is also expensive, that is why I am looking for a solution using a 555 chip design or something similar. Is there some way to create a multiplier of the 555 kit timing so that R3 100k ohms= 24 hours and R3 250k ohms = 72? The diagram above is kit. I can can change R4 and C1.

 

555's just aren't very good for long time periods. Cheap 24 hour timers, even with on-to-off minimum times of 15 minutes will work. The AC output would be coupled to a 20-second 555 monostable. The monostable only reacts to the turn-on, not the on-time. The turn-on would also "clock" a counter, advancing it one position each 12 hours. You would select the output that coincides with the time you want. After that period it outputs a 20 second signal and resets the counter.

Ken

 

Ken,

Sent you a PM...

 

555's just aren't very good for long time periods. Cheap 24 hour timers, even with on-to-off minimum times of 15 minutes will work. The AC output (of the timer?) would be coupled to a ("a" or "the") 20-second 555 monostable. The monostable only reacts to the turn-on, not the on-time.

If the output of the cheap 24 hour timer on/off is (say 15 minutes) less than the output of the 555 monostable, then all is well.

The turn-on would also "clock" a counter, advancing it one position each 12 hours. You would select (x unit = 12, 2x =24?) the output (what device? a second 555?) that coincides with the time you want. After that period it outputs a 20 second signal and resets the counter.

Ken

Ken,

My state of confusion is clearing somewhat...

This is what I think you are saying: "The" 20 second monostable 555 runs a 12v motor. (Jeffrey nods "yes")

The 24hr timer can be set for every 12 hours creating X unit that is counted as 1x, 2x, 3x. The (or "a" ?)device counts input X and triggers output when selected value of X is achieved (2x or 6x)(24hrs or 72hrs).

Question: Does the 24hr timer create X units, count X, 2x, 3x, and then output A (which is then coupled to trigger 20sec/mono/555?), or do I need another device/component?

 

Ken,

Here is a link to the Intermatic Digital Switch timer. It has 7 on/off settings per day, and also allows different settings for each of 7 days (Monday-Sunday).

http://www.intermatic.com/?action=prod&pid=9232&did=5&cid=43&sid=112

 

I agree the prebuilt time is the easier option. They don't switch times that easily, but are reliable and accurate.

If you are feeling adventurous a couple of 4060's (I figure 3) with a couple of inverter chips for logic decoding would do the trick, followed by the 555 would do the trick. 30 minutes accuracy in 24 hours is still pretty tight, so you would want to use the crystal option.

Part of the reason everyone recommends the 4060 is it is pretty simple. I haven't build with it yet, but this is redrawn out of the datasheet.

The crystal option shown will output 2Hz out it lowest freq, but you can feed this into another 4060 X2.

 

Thanks for the input Bill... I was hoping you would have a look here!

 

Bill,

The datasheet you linked me to from TI, says the product is discontinued?

 

Jeff,

After our phone conversation I have a better picture. The digital pool timer will take care of the 24/36/48/72-hour timing. You needed a power-up, 20-second monostable, powered by the pool timer and outputting to a relay controlling the 12VDC motor. The Ramsey timer will work as shown. C1 needs to be a 220uF/16v for the 20 second timer.

Ken

 

http://www.zen22142.zen.co.uk/Circuits/Timing/ivt.htm

The time range posibilities goes out to 32 hours, but could probably be stretched to 72.

How accurate does your timer have to be? Like a clock? Or can it be off a few minutes or an hour over 4 days?

Ken

LM555 IS VERY STABLE.