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Make electronics : experiment 8 problem

harley quinn

Jul 23, 2015
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Hi, I was wondering if you could help me ?.
I built this circuit and D2 stays lit while D1 flashes while I press the button .Is this what is supposed to happen?.
I am new to this if you could explain that would be cool.
upload_2015-7-23_15-58-7.pngThank you.
 

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Minder

Apr 24, 2015
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Usually the bottom two of the relay is the coil, you appear to have the connections mixed up?
M.
 

Minder

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You need to identify the actual relay used, some also have the common for the contacts in different positions.
M.
 

harley quinn

Jul 23, 2015
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You need to identify the actual relay used, some also have the common for the contacts in different positions.
M.
This is the relay in my circuit M.
upload_2015-7-23_21-44-1.png
Any ideas ?
 

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Minder

Apr 24, 2015
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I agree, the circuit does not make alot of sense?
Where did you come up with the circuit?
Also the relay part No is a 5v version, instead of 12v.
M.
 

harley quinn

Jul 23, 2015
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First of all, what is the circuit supposed to do?????
Hello Colin,
When you you press the button, D1 is supposed to light up.Then it goes out when the coil charges in the relay which switches on D2 .The capacitor is supposed to give the coil an extra boost to keep the switch to D2 on for about a second after which the relay goes back to NC, charging the capacitor and charging the coil and lighting D1.
My problem is D1 stays lit and D2 flashes , I would like to know why D1 stays lit.
 

harley quinn

Jul 23, 2015
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I agree, the circuit does not make alot of sense?
Where did you come up with the circuit?
Also the relay part No is a 5v version, instead of 12v.
M.
Yes , Sorry my relay is the 12v version. Well observed. The circuit comes from Make electronics book, experiment 8.
 
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harley quinn

Jul 23, 2015
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Someone beat this horse to death more than three years ago in this thread. Also Google has a lot to say about it.
HI hevans1944,
I have seen the flogging of this horse, which included problems an autistic man was having with this circuit .The thread
was very long and did not answer why the first led stays lit while the second one flashes. I checked your google link. Thank you.
Again I found no answers .Only another person with the same problem. http://www.davissemi.com/2013/08/make-electronics-experiments-7-and-8.html. Just a quick explanation. Why does the first led stays lit, while the other flashes. Would be good if you have any ideas ? .Thanks
 

KJ6EAD

Aug 13, 2011
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harley quinn

Jul 23, 2015
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First of all, what is the circuit supposed to do?????
I've attached the relevant images from the text. Which one represents your current problem?

When using that book, keep this link handy and check it for errors in each experiment before starting them.

http://www.oreilly.com/catalog/errata.csp?isbn=9780596153755
Hello there,
mkel_02_065.pdf and mkel_02_066.pdf represents the circuit .I checked the errata, couldn't find any explanation of the problem of one led staying lit while the other one flashes. Any ideas KJ6EAD ?.
 
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hevans1944

Hop - AC8NS
Jun 21, 2012
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Hi, I was wondering if you could help me ?.
I built this circuit and D2 stays lit while D1 flashes while I press the button . ...
...
My problem is D1 stays lit and D2 flashes , I would like to know why D1 stays lit.
So which way is it? Does D2 stay lit and D1 flashes, or does D1 stay lit and D2 flashes?

This circuit doesn't really teach you much of anything about electronics, does it? Except, maybe, it's not a good idea to try to energize a relay through its normally-closed contacts, because that is an unstable configuration.
 

KJ6EAD

Aug 13, 2011
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I suspect that you have a simple wiring error. Be sure that you're working from a correct pinout for the relay you have, not just blindly following a pictorial diagram. Use a meter or even a simple improvised test light to verify the relay contact form.
 

Colin Mitchell

Aug 31, 2014
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I have redrawn the circuit to make it much easier to see what is happening.
D1 remains lit all the time after the button is pressed because when you push the button, the current goes around the circuit, through the top relay contacts and then through the LED and through the 680R resistor.
During this time the 1,000u charges and when it has a certain voltage across it this voltage is also passed the the coil and it produces magnetic flux that pulls the clapper towards the image of the relay on the circuit and this changes the contacts. The result is the other LED illuminates.
No here is the clever part. The positive voltage from the switch does not go to the first LED and you would think it goes out.
But the voltage across the 1,000u takes over and supplies voltage and current to both the LED and relay to keep them both activated.
After a short period of time the voltage drops to a point where the relay "opens" and the second LED goes out.
This voltage is too low to keep the relay activated but it will still keep the first LED illuminated a small amount.
The relay changes to the other set of contacts and now the voltage from the switch takes over to keep the first LED illuminated and the cycle repeats.
This is all clearly written in the mind of the author of the book, it is just unfortunate that he did not put it on paper.


Relay-1.gif
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Thank you @Colin Mitchell for that clear and succinct explanation. One should also realize that after pressing the switch a certain pull-in current appears in the relay coil and that this pull-in current is always greater than the drop-out current, below which the contacts revert to their de-energized position. As you said, this holding current, whose level is between the pull-in and drop-out current levels, is provided by the charge stored on the capacitor.

I should also mention that this circuit has almost zero application in real, practical, electronic circuits. There are much better ways to make a relay coil energize and de-energize on a repetitive basis at consistent and predictable intervals. Can we bury this horse again?
 

harley quinn

Jul 23, 2015
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So which way is it? Does D2 stay lit and D1 flashes, or does D1 stay lit and D2 flashes?

This circuit doesn't really teach you much of anything about electronics, does it? Except, maybe, it's not a good idea to try to energize a relay through its normally-closed contacts, because that is an unstable configuration.
D1 stays lit ,D2 flashes.
 

harley quinn

Jul 23, 2015
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I have redrawn the circuit to make it much easier to see what is happening.
D1 remains lit all the time after the button is pressed because when you push the button, the current goes around the circuit, through the top relay contacts and then through the LED and through the 680R resistor.
During this time the 1,000u charges and when it has a certain voltage across it this voltage is also passed the the coil and it produces magnetic flux that pulls the clapper towards the image of the relay on the circuit and this changes the contacts. The result is the other LED illuminates.
No here is the clever part. The positive voltage from the switch does not go to the first LED and you would think it goes out.
But the voltage across the 1,000u takes over and supplies voltage and current to both the LED and relay to keep them both activated.
After a short period of time the voltage drops to a point where the relay "opens" and the second LED goes out.
This voltage is too low to keep the relay activated but it will still keep the first LED illuminated a small amount.
The relay changes to the other set of contacts and now the voltage from the switch takes over to keep the first LED illuminated and the cycle repeats.
This is all clearly written in the mind of the author of the book, it is just unfortunate that he did not put it on paper.


View attachment 21153
Thank you. I think I understand. When the relay switches on and the power is cut to the coil, the capacitor powers the coil for about a second keeping the switch on but it also powers D1, so it looks like D1 stays lit. Is that it ?. I hope i have understood your very good explanation. I think the book should have been clearer.
Thanks again.
 
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harley quinn

Jul 23, 2015
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Thank you @Colin Mitchell for that clear and succinct explanation. One should also realize that after pressing the switch a certain pull-in current appears in the relay coil and that this pull-in current is always greater than the drop-out current, below which the contacts revert to their de-energized position. As you said, this holding current, whose level is between the pull-in and drop-out current levels, is provided by the charge stored on the capacitor.

I should also mention that this circuit has almost zero application in real, practical, electronic circuits. There are much better ways to make a relay coil energize and de-energize on a repetitive basis at consistent and predictable intervals. Can we bury this horse again?
I only persisted with trying to understand because the book ' make electronics ' didn't explain that this would happen. I am trying to learn and i hope the book is a lot clearer in the future .If not , i may have to ask a question, i hope that is ok .I will try not to dig up any
horses that have been beaten to death. Thank you all.
 
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