harley quinn
- Jul 23, 2015
- 11
- Joined
- Jul 23, 2015
- Messages
- 11
How would I change the connections Mr Minder?Usually the bottom two of the relay is the coil, you appear to have the connections mixed up?
M.
Hello Colin,First of all, what is the circuit supposed to do?????
Yes , Sorry my relay is the 12v version. Well observed. The circuit comes from Make electronics book, experiment 8.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.
HI hevans1944,Someone beat this horse to death more than three years ago in this thread. Also Google has a lot to say about it.
First of all, what is the circuit supposed to do?????
Hello there,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
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 . ...
So which way is it? Does D2 stay lit and D1 flashes, or does D1 stay lit and D2 flashes?...
My problem is D1 stays lit and D2 flashes , I would like to know why D1 stays lit.
D1 stays lit ,D2 flashes.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.
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.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
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 anyThank 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?