# Digital Circuit

Discussion in 'The Projects Forum' started by pbhuter, Sep 17, 2012.

1. ### pbhuter Thread Starter New Member

Sep 17, 2012
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Quite some time ago, as an undergraduate student, I took a course in Digital Circuits. It was a very interesting course, but looking through the textbook (I would look at my notes if I could find them...), I am unable to solve this problem I have:

I want to design a circuit that will apply an electric current for a period of time (controlling the length of time would be nice...), then "open a switch" (either on the IC or through a diode or something) to allow an electric current to flow for a period of time (again, control here would be nice).

Does that make sense?

I'd like to keep things simple: IC(s), wire, battery (and maybe diode). I will need to know what kind of IC(s) to use, and how to hook things up/program things.

In advance - Thank you for any/all assistance.

2. ### wayneh Expert

Sep 9, 2010
12,151
3,058
Not one bit!

Details matter, so be as specific as you can. Voltage, current (into what?), timing (frequency? repeating or one shot?), lay it all out in detail. Off hand it sounds easy but no one can tell without the details.

pbhuter likes this.
3. ### pbhuter Thread Starter New Member

Sep 17, 2012
8
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For the initial "experiment" of this project, I intend to use a 9V battery. For sake of providing details (keep in mind, I'd like to be able to experiment with the following to come up with an optimal solution): five second of "on" for the current (from the 9V battery), five second "wait", five seconds for the current to pass back (through the diode or whatever). This three-phase cycle will be repeated until shut down.

Does that help?

4. ### Dodgydave Distinguished Member

Jun 22, 2012
4,999
745
I would use a 555 timer clocking a CD4017 decade counter set to 3, the 555 will be clocking at 5 sec cycles, then you will have three outputs from the decade counter each will go high every 5 seconds.

Does this help?

5. ### Austin Clark Member

Dec 28, 2011
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What do you mean by "five seconds for the current to pass back"? Either way, are you looking for some sort of digital oscillator? Where, in essence, the power is turned on for five seconds, turned off for five seconds, turned on for five seconds, etc; and used to drive something?

If so, there are quite a few options. Astable multivibrator or a 555 timer, for example.

6. ### wayneh Expert

Sep 9, 2010
12,151
3,058
+1
Take your output by comparing digital out pins 1 and 2. On the count of 1, current can flow from 1, which is high, to 2, which will be low. On the next tick of the clock, the polarities reverse. Compare 1 to 3 to get a pause on 2, since 1 and 3 will both be low at that point. Reset the timer on 3 or 4 depending on what timing you want.

If the 4017 can't handle the current you want, you'll need to amplify with an op-amp.

7. ### pbhuter Thread Starter New Member

Sep 17, 2012
8
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I realized that what I really need is a two-step cycle: Current on (for a variable period, but say five seconds for now); allow other current to move (five seconds, again?).

I see lots of part numbers, for ICs I assume, but I was hoping for some more help. I'm an Aerospace Engineer, I took a single Electrical Engineering course and the aforementioned Digital Circuit course, but that was about 10 years ago. So, any help to help me actually design and build this circuit would be appreciated.

Thanks for the help so far, and any future assistance.

8. ### wayneh Expert

Sep 9, 2010
12,151
3,058
I still don't get this. What is the "other" current?

Turning something on and off at 0.1Hz (5 seconds on, 5 off) is easy, but we don't understand what happens throughout the cycle. And you still haven't said how much voltage and current is applied while "on", let alone "off".

9. ### crutschow Expert

Mar 14, 2008
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A simple circuit diagram showing switches configured to do what you want would be helpful. We can then tell you how to control the switches.

10. ### elec_mech Senior Member

Nov 12, 2008
1,513
193
I'd suggest you write step-by-step how you'd like the circuit to operate. Based on the information provided so far, it would look something like this:
1) Turn on circuit.
2) Circuit provides power to something rated at X (AC or DC) volts and X current for 5 seconds.
3) Circuit disconnects power to same something for 5 seconds.
4) Steps two and three repeat indefinitely until circuit is turned off.

We'd like to know what that something is - a motor, light, etc. - and what is it rated at (voltage, AC or DC, current). We'd also like to know what the max and min delay time you'd like ultimately, e.g., 5 seconds to 20 seconds?

11. ### pbhuter Thread Starter New Member

Sep 17, 2012
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1) Turn circuit on (probably just connect 9V battery)
2) Circuit runs current through a coil of wire (I know I said for 5 seconds, but really - since electricity is instant - time doesn't really matter)
3) Stop running current through coil
4) Allow "discharge" from other side of circuit (through diode?)

So we have two sides, one connected to a coil, one just connected to a wire. I'm thinking a rechargeable battery would work here, so the "discharge" has somewhere to go.

12. ### elec_mech Senior Member

Nov 12, 2008
1,513
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There is a misunderstading here somewhere. What do you mean by "discharge"? Perhaps if you could post a simple drawing of what you are picturing, we can explain this better.

Steps 2 and 3 don't quite make sense. The power has to be applied for some amount of time whether that be 1 second or a week. By your description, it would be like flipping a light switch on and off as quickly as possible - you may see the bulb flicker in that half second, but it won't be turned on. If you're just sending a brief high signal to something, that's fine, but we have to know what it is you are doing.

You say put electricity through a coil of wire. Again, what is it you intend to power? What is its purpose?

13. ### pbhuter Thread Starter New Member

Sep 17, 2012
8
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Not sure if this explains things.

I want to build a negative electric field, which will cause a shift separating protons and electrons, and I will discharge the electrons.