Hi folks. I hope it's OK to post this question as my first post to the forum. I have no electronics skills (that will be quickly apparent!) but I do have a basic understanding of DC circuits and can manage a soldering iron.
My main hobby is traditional (darkroom) photography and I need a timing device that will power a gadget to rotate my film developing tank for me. I need to be able to reverse the direction of rotation at set intervals, and I need to allow the motor to come to a complete stop before reversing the direction.
The gadget is built, and works, powered by a 12v 4rpm geared motor that according to the specs draws 200 ma. I've tested reversing the motor manually with a DPDT centre-off switch wired for reversing polarity. Now I wish to automate the process of reversing the polarity.
The cycle of operations I want is as follows:
Timers 2 & 3 are configured to deliver 12v DC to the motor in different polarity, thus reversing the direction of rotation. The motor needs a 2-second OFF time between changes in direction. Timers 2 & 3 are each set to cycle ON (27 seconds) - OFF (5 seconds) - ON - OFF - continuously while powered.
Timer 1 controls switching between Timers 2 & 3 through the SPDT relay. Timer 1 is set to cycle ON (30 seconds) - OFF (30 seconds) - ON - OFF continuously while powered. Note that this ON cycle is shorter than the total ON-OFF cycle time of the downstream Timers. Timer 2 will complete its 27-second ON time and 3 seconds of its OFF time before it loses power as Timer 1 switches power across to Timer 3, which repeats the same cycles but outputs with reversed polarity.
Now my questions:
First - will this work? (Assuming I have understood what the timer does.)
Second - do I need to put a diode into each of the + wires between the timers and the motor, to protect the dormant timer from + current flowing into the timer from the wrong direction? If yes can you please suggest a value or specification (or better yet a Jaycar part numbr ).
I understand there must be smarter / more elegant / cheaper ways to do this, but due to my total lack of electronics knowledge I have to make use of parts I understand and can put together to suit my needs.
Sorry for the long post - thanks to anyone who can take a look and advise me. Cheers!
Chris.
My main hobby is traditional (darkroom) photography and I need a timing device that will power a gadget to rotate my film developing tank for me. I need to be able to reverse the direction of rotation at set intervals, and I need to allow the motor to come to a complete stop before reversing the direction.
The gadget is built, and works, powered by a 12v 4rpm geared motor that according to the specs draws 200 ma. I've tested reversing the motor manually with a DPDT centre-off switch wired for reversing polarity. Now I wish to automate the process of reversing the polarity.
The cycle of operations I want is as follows:
- Switch on
- motor runs clockwise for 30 seconds (or thereabouts)
- motor stops for 2 seconds
- motor runs anti-clockwise for 30 seconds
- motor stops - and the cycle repeats for as long as I leave the whole thing turned on, usually 20 minutes to two hours (manually controlled, because I have to be there to empty the tank immediately the time period is up).
- ability to set a suitable time interval independently for ON time and OFF time;
- ability to reprogram different times for both ON and OFF cycles as I experiment with the gadget and different films and developers; and
- ability to set the ON - OFF cycle to repeat continuously.
Timers 2 & 3 are configured to deliver 12v DC to the motor in different polarity, thus reversing the direction of rotation. The motor needs a 2-second OFF time between changes in direction. Timers 2 & 3 are each set to cycle ON (27 seconds) - OFF (5 seconds) - ON - OFF - continuously while powered.
Timer 1 controls switching between Timers 2 & 3 through the SPDT relay. Timer 1 is set to cycle ON (30 seconds) - OFF (30 seconds) - ON - OFF continuously while powered. Note that this ON cycle is shorter than the total ON-OFF cycle time of the downstream Timers. Timer 2 will complete its 27-second ON time and 3 seconds of its OFF time before it loses power as Timer 1 switches power across to Timer 3, which repeats the same cycles but outputs with reversed polarity.
Now my questions:
First - will this work? (Assuming I have understood what the timer does.)
Second - do I need to put a diode into each of the + wires between the timers and the motor, to protect the dormant timer from + current flowing into the timer from the wrong direction? If yes can you please suggest a value or specification (or better yet a Jaycar part numbr ).
I understand there must be smarter / more elegant / cheaper ways to do this, but due to my total lack of electronics knowledge I have to make use of parts I understand and can put together to suit my needs.
Sorry for the long post - thanks to anyone who can take a look and advise me. Cheers!
Chris.
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