# non electronic person needs help

Discussion in 'The Projects Forum' started by Hutch01, Jun 30, 2011.

1. ### Hutch01 Thread Starter New Member

Jun 30, 2011
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I am not an electronics person, although I have a basic understanding of gates, transistors, etc. I would like to make a circuit that would have an incoming voltage of 24v 1amp and switch the output to one of two outputs each time the incoming voltage goes high or low. ie: input high output to A, input is off no output to either Outputs A or B. Input goes high again output goes to B. input goes off and output switches to off. the output would be 24v 1amp same as the input. this would be a repetitive cycle between outputs A and B. Thanks in advance.

2. ### #12 Expert

Nov 30, 2010
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The alternating part is what needs to be designed. One way is to use a flip-flop chip and have that choose between 2 relays or SCR's. I don't think you can buy an alternating relay. Some of the younger people will instinctively go for a microcontroller chip and try to program the function. I suppose it could be done with discrete design (single transistors), maybe even several relays!

The problem is, you can't just order an 24 volt alternate switcher and plug it in.

3. ### ifixit Distinguished Member

Nov 20, 2008
639
110
Hi Hutch01,

Here's a circuit idea using transistors and some CMOS logic. It still needs work, but it is a start.

Is this the function you want?
Is it something you think you can build?
What is the minimum ON time expected?
What is the maximum OFF time expected?

Im guessing the logic control circuits need to be powered from the toggling 24V input. Is that correct?

It would be better if there was a +5V power source that is always present so the toggling can be consistent, even if the OFF time is very long.

Anyone have any simple solutions on how to remember a logic state without power on?

Regards,
Ifixit

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4. ### Ron H AAC Fanatic!

Apr 14, 2005
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Can you define the on and off times? Are they periodic, or random?

5. ### CDRIVE Senior Member

Jul 1, 2008
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The TIP42 has a max hFE of 75. It could be a low as 20. Since the OP needs to source 1A those 2K resistors are too high to garantee saturation. The general rule for saturated transistors is Ib=Ic/10.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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A 10V or 12V zener and PMOS switches would be a better solution, but we need to know about the times involved before we can know if that scheme will work.

7. ### Hutch01 Thread Starter New Member

Jun 30, 2011
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Ok here is the senario, I have a programable controller. I want to use 1 field wire to controll to items. The controller has more outputs available than there are field wires. adding more field wires is not possible but adding devices to be controlled is possible. So, I jumper from lets say output 7 to 8 and from 8 to the field. lets say 7 goes high for 20 minutes every other day. Next 8 goes high for 20 minutes every other day, (same days). The rest of the time they are off. From the one field wire would come the source of the single input going high for 20 minutes, then low, then high again for 2o minutes, then low for the next 48 hours. when it goes low I want to swith outputs to the next output. These are just expample times off and on, they may be lower or higher. It is an irrigation application. There are devices like what I want for sale but pricy. I have the ability to make something myself just need some guidance. Thanks

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8. ### strantor AAC Fanatic!

Oct 3, 2010
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you can set the timer relay to something other than 500ms, I just chose that because it sounded like a good number, enough time to energize the coil.

Last edited: Jul 1, 2011
9. ### ifixit Distinguished Member

Nov 20, 2008
639
110
Hi Strantor,

I like the simplicity of your relay design, the OP can likely build this easier if it works. However, I think it will oscillate the way it is wired now. Perhapes a single-coil latching relay might work better, it has a rotating mechanical device to hold the state after the coil is de-energized.

My circuit will need a battery or something to keep the logic powered so the state can be remembered for days. Back to the drawing board.

Regards,
Ifixit

10. ### strantor AAC Fanatic!

Oct 3, 2010
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I neglected to mention that the time on the time delay relay should be set as low as possible- to where the dual coil relay energizes exactly one time, to prevent oscillation. I've never tried it, but it seems sound in my mind. I cannot picture what you mentioned about a single coil latching relay - never seen one, but I will look into it - may be much better.

11. ### strantor AAC Fanatic!

Oct 3, 2010
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Taking this idea, I read up on all the types of relays, specifically latching ones. I came across this writeup and read about the Impulse Relay. Seems to satisfy the requirements in one package. It is designed to have a pulse, but from the way I read it, it shouldn't matter if the signal is maintained, because the switching happens when it tranistions from 0 to 1.

I searched for impulse relay on newark and got this. 24V for 45\$. I think it will do the trick.

just do like so:

Ah, but apparently you can!
Ironically, It's a plug-in type

looks like yes.

12. ### #12 Expert

Nov 30, 2010
16,705
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Keep this handy. I've seen dozens of people looking for something like this, and in your travels, watch for impulse relays that count to 3,4,5 and more.

It would also be nice if they could be bought for less money!

Jul 17, 2007
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14. ### strantor AAC Fanatic!

Oct 3, 2010
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but then you would need another relay to reverse the current, right? which is a similar scenario I proposed in post #8.

15. ### ifixit Distinguished Member

Nov 20, 2008
639
110
Hi Strantor,

Well done. I like it so far.

Hutch01 wrote:
I agree with the OP that it would be best if the state change was during the OFF period, or as least during transition to OFF. This would avoid glitches that will occur if done during the transition to ON. If glitches are okay then it doesn't matter. We need input from the OP.

Is there an impulse relay that operates as power is being removed?

Regards,
Ifixit

16. ### strantor AAC Fanatic!

Oct 3, 2010
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From the write-up:
So, I guess to get the operation that you are suggesting, it would have to have a capacitor to store enough charge to energize the coil after power is gone.
I don't understand why detecting & switching the state when power is applied makes it any more prone to glitches than otherwise. Would they market a relay that is glitchy? The way I see it, it's simpler to do it the way it's being done.

Jun 30, 2011
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It's 24v AC

18. ### Hutch01 Thread Starter New Member

Jun 30, 2011
7
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Keep in mind this circuit is 24v AC

Oct 3, 2010
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Jun 30, 2011
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