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Delay ON, using a 555 and 12v motor

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JeremyA

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Hey guys,
Please bare with my ignorance, but I have been searching for an easy to make circuit for something I am working on, but I have had no real luck finding a good explanation on how it works, or a good schematic. Here is what I got.
I have a 12V DC motor. I have cross-wired a DPDT toggle switch so I can reverse the motor. What I need is a circuit that will have a variable time delay before the motor starts running in the opposite direction. I have a 10K potentiometer that I would like to use as the time delay. I am shooting for 15-20 seconds of power off time before the motor starts again. I would like to have a 0-60 second time delay but I can work that out when I understand this circuit better. I have a few 555 chips and a box full of components. I have read that the chip is safe running at 12v, but I am not sure how the circuit would work or look once the current is reversed. Can someone help me to understand? Thanks in advance.
 
How much current does the motor draw when stalled?
 
These are one of those times where I will thank you in advance for not getting annoyed with my lack of intelligence on electronics, but I am not sure what you mean "when stalled". I would assume the motor draws 0 current, but I also realize I know nothing about all of this. Here is the motor I have. Amico DC 12V 0.07A 3.5RPM High Torque Gear Box Electric Motor 37mm.
 
Welcome to ETO, JeremyA!

A "stalled" motor means a motor that, while powered, cannot turn. This creates a situation where the current through it is at a level considerably higher that its normal "running" state (200-600mA value listed for that motor). alec-t asked the question since the stall current dictates some of the design of the timer circuit. The stall current also reflects the current the motor draws when first powered up, also higher than the normal run current level.

The various vendors I checked did not list a stall current. I'm going to assume 1A (65% over-current).

To introduce a delay, ... (I'm working on it - unique problem) :woot:
 
I really appreciate the effort and the explanation. I googled stalled current after I posted and it sort of explained. I tried to find the motor spec, but no such luck. You explained it perfect. Does that help determine what size of resistors and capacitors required?
 
Thanks for the welcome also. I have received so much knowledge from this forum in the past, I figured all of you would be the best to ask.
 
Hi Jeremy. Can you state the problem in full? How long does the motor go forward? How long in reverse? Are you using limit switches? Does the motor repeat e.g. forward x0 seconds, wait x1 seconds, reverse x2 seconds, wait x3 seconds, forward x0 seconds, wait x1 seconds, ... etc. ?
 
My limit switch should be the toggle. I realize it might take (2) 555 timer chips. I will try to explain the situation. I have a 3.5 rpm 12v dc motor. I want to run the motor forward to infinity at start up. Once it hits the limit of distance (toggle opposite), I want a 0-60 second delay (potentiometer). So the motor stops or waits to reverse for the time my pot... Is dialed to. Then it runs to it's other limit of distance (infinity till toggle forward) and delays again for the same amount of time as first delay. It will be completely automatic unless there is loss of power. In that case, the toggle dictates in which direction the motor runs. I'm sorry if this is confusing.. it's difficult to explain something I have no clue about.
 
That clarifies your requirement and gives us a better starting point, but I don't think your DPDT toggle switch (which I assume is a manually-operated switch?) will be part of the solution if you want this system to run automatically.

It will be completely automatic unless there is loss of power. In that case, the toggle dictates in which direction the motor runs.
Surely loss of power means the motor won't run at all?
 
This works:
555 Delayed Rev Motor.JPG


... I want to run the motor forward to infinity at start up. ...

To achieve this start-up condition (NO delay at initial system 'Power-up"), one or the other of the "Start" push buttons (depending on the position of the toggle) must be pressed. This simply terminates the initial delay at power up. After that, the motor will continue, reversing rotation (following any delay set by either of the two potentiometers) after each DPDT toggle switch change.

Any power up after a power loss, regardless of the toggle switch position, is the same as a start-up, so the above action(s) will be necessary if a delayed start is not acceptable.

<EDIT> Assuming CW rotation of the motor with appropriate polarity observed, upper timer is CW delay circuit and lower is CCW delay circuit. DPDT toggle is shown in CW start position.

This is DPDT SW in alternate state:
DPDT SW.JPG
 
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If it makes it easier, I can replace the DPDT toggle with a push button. I wanted to use the toggle because it reverses the DC motor and power was always on. Let me try to explain what I am doing. My Dad is a model train fanatic. He has made this large scene downstairs and I wanted to help him make a backdrop. I am using Unistrut and I have already bought the motor, and made the motor enclosure. I mounted this box with some roller bearing above it, so the motor shaft raises up inside the channel, and using a small wheel, mounted to the tip of the shaft to drive the motor carriage one way or the other. My vision on this is to have the motor carriage get so far to one end, hit some sort of stop (toggle opposite), then have a delay of time (variable), then start in the opposite direction till it hits the other end stop. There it will pause on a delay before reversing again. etc. etc. over and over until my dad turns off all the power to the scene. I have no problem going down to the shack and buying some push button switches, just was not sure what to get and I already have a toggle wired up.
 
OK cowboybob, now we are getting somewhere! I am assuming the potentiometers are at the 1m location? So I would have to set both pot. controls, one for either direction? also, why is there a 4m resisitor on the bottom and not the top chip?
 
Here is the motor carriage as it would appear mounted with unistrut. I can bolt or attach an angle to either end of the strut so when the motor gets that far, it trips the toggle the opposite way and then the delay/pause happens, motor reverses. This sequence happens over and over again. Hope this helps to explain myself.
 

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sorry, yes alec, loss of power means motor is not moving. I am running this from a 12v power adapter from my wall. No battery back up or anything. fyi.
 
Also, is there a certain size of diode I need? (I am assuming D1 & D2 are diodes). Are those "Start" forward and reverse buttons momentary buttons? So they should NOT lock in on a push and unlock with another push. Are they there just to let the circuit know which way run? Thanks again for your help guys.
 
Oops.
Corrected schematic (no 4M resistor [capital "M" for MEG Ohm]):
555 Delayed Rev Motor.JPG


Diodes can be 1N4004. "Start" switches are momentary push-button types. Their use terminates the delay period timer they're attached to.
 
great. I will work on getting the components I do NOT have tonight and hopefully test this out on my breadboard. I will let u know how things progress. Thanks a ton Bob.
 
Please note schematic change:
Start Sw Mod.JPG

Minor, but improves delay termination.

Midrange on a pot will produce a delay of approximately 55 seconds.
 
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Bob,
I have a question for you and I am sure you did it your way for a reason, but I wanted to know why to better help me understand circuits.. Take a look at my .pdf... What would happen if we eliminated the lower 555 and tied the diode in this way?
 

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Jeremy, your modified circuit won't be able to retrigger (the 1uF capacitor on the trigger pin will remain high after the initial relay activation). You could try something like the following mod. It relies on the DPDT switch being a break-before-make type, which will allow a small low pulse to be fed into the trigger pin when the motor hits an endstop and toggles the switch.
upload_2014-4-17_21-52-30.png
 
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