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Will this circuit work out of curiosity? Answered

I saw a question, https://www.instructables.com/answers/Need-help-with-the-wiring-diagram/ that asked about making a relay circuit that is capible of moving or rotating something to one extreme, then stop, and reverse direction to go the other way, but what intresting is that there is also supposed to be a delay in it, so it goes all the way in one direction, stops for a moment, and reverses direction and stops, then reverses... you get the idea. That question intrigued me, as I like really basic and elegant solutions that do not use a raspberry pi to do such a demeaningly simple task!

I can see something like that being used for an automatic door w/ one button operation, and I decided to see what I can come up with on my own with a few relays on paper. Here was my solution. However, although I have traced it all out and it seems to be functional, can anyone else verify that? When I get the parts, I will actually try to build a scale model to and see how well it works (after all, thats the best way to discover problems! The physics engine of real-life is never wrong :) ). I may modify it so it just uses a "open" and "close" switch instead w/ the limit switches. (a bit more practical for that use.) But I wanted to challenge myself with those requirements instead.

The idea here is that I have 2 DPDT switches, the 1st one will be a latch, and the second one will change the polarity of the motor. There is a giant RC circuit on the output of the 1st relay which delays the changing of polarity to the motor using the 2nd relay (as an H bridge), and the limiting switches control power to the motor in one or the other direction, (so when one limit is hit, the power cannot continue to flow through the into the motor, so it does not keep trying to push the switch off, but still must allow the polarity to be reversed and let the motor travel the other direction to the other side, so it does not freeze up right there. Thats needed because the same RC circuit which delays the polarity switching is 'laggy' and the capacitor takes time to discharge, and it will continue to try to press that motor into the switch until the capacitor has discharged fully though the relay coil. Just not good engineering practice.) 

2 Replies

-max- (author)2015-03-22

I am having trouble figuring out what you have changed, it looks perhaps a bit enhanced with MS paint, but other than that, I cannot see any electrical difference.

Or are you showing the process for which it works? I have done that in the image showing all the blue and red arrows on my note 3, although I only uploaded the final thing after lots of scribbling.

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-max- (author)2015-02-24

I figured that relay latch should work, but what about the H bridge portion of it? What can cause it freeze up in some steady state and not work?

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