Reversing motor circuit

Thread Starter

Mikel333

Joined Jan 28, 2013
6
I built the circuit suggested by SgtWookie in 2007 for the purpose of running a motor in one direction until it hits a limit switch then after a short interval reversing the motor until a second limit switch is reached. I used the 555CN for the timer circuit. The motor runs in one direction but when it hits the limit it stops and that is it? I am not sure if anyone would be familiar with this project but I could really use some help.

Thanks
 

antonv

Joined Nov 27, 2012
148
That's a long time ago. Does it use a relay to control the motor? If you have a schematic you can post that will be good.
 

praondevou

Joined Jul 9, 2011
2,942
With RLY1 energized , does the motor turn in the direction to activate (open) S1? Is it possible you inverted the switches? Is the 555 ON time about 37s?

The ON time is fixed and doesn't depend on the position of the switches, maybe it's just too long for your application?
 

BillB3857

Joined Feb 28, 2009
2,547
Can you post a link to the 2007 thread. Something doesn't look right. When S1 opens, and the output of the 555 is LOW, there is no path for bias to turn Q3 on, unless I'm missing something. It looks like you need a resistor from Q1 Collector to +12
 
Last edited:

praondevou

Joined Jul 9, 2011
2,942
Can you post a link to the 2007 thread. Something doesn't look right. When S1 opens, and the output of the 555 is LOW, there is no path for bias to turn Q3 on, unless I'm missing something. It looks like you need a resistor from Q1 Collector to +12
Yes, correct.

This is the sequence:

Motor not activating none of both switches.
555 out = 0
Q3 and Q2 conducts, RLY2 is energized, motor turns
S2 is activated, motor stops
555 out = 1
Q1 conducts (Q3 and Q2 do not conduct), RLY1 is energized, motor turns in other direction
S1 is activated, motor stops
555 out = 0

Now S1 is open, everything stops.

Do what BillB suggested.

The original diagram was posted here:http://forum.allaboutcircuits.com/showthread.php?t=61897
 

BillB3857

Joined Feb 28, 2009
2,547
Remove the 555 from its socket. Temporarily connect Pin 3 of the socket to Vcc. R1 should pick up and the motor run until it hits the FWD limit. At that time, R1 will drop out. Now connect Pin 3 of the socket to Gnd. The R2 should pick up and the motor reverse. Let us know the results. It almost sounds like your limit switches are in the wrong legs and your motor is simply stalling.
 

Thread Starter

Mikel333

Joined Jan 28, 2013
6
When connected to Vcc the motor ran to the first limit and stopped but when connected to ground nothing. I have voltage at relay2, I will check in the morning to make sure the relay is good.

Thanks
 

tubeguy

Joined Nov 3, 2012
1,157
It wouldn't hurt to have one, but wouldn't the Emitter/Base junction of Q2 provide that function?
With no pullup Q3's collector and Q2's base will be in a floating, indefinite state when Q3 is off. The circuit might work but IMO it's good practice to use a pullup to be sure that Q2 is fully off when Q3 is turned off.
 

Thread Starter

Mikel333

Joined Jan 28, 2013
6
I'm not sure I follow on the "pullup"? Let me explain a bit, I'm a machinist helping some high school students to construct a platform that slides into a pipe 12 inches, stops for about 30 to 60 seconds and then returns to start. It needs to do this once every demonstration not continually. I am very limited in my electronic skills. Could you explain what I need to put the "pullup" into the circuit?

Thank you very much.
 

BillB3857

Joined Feb 28, 2009
2,547
The circuit we have been describing will cycle as long as there is power. If you want it to make one round trip, then stop there will need to be some modifications. First, to answer you question about Pull Up resistors. The resistors in RED are called Pull Up resistors because they Pull the base or collectors of their attached transistors UP to the +12V level, but at the same time, limit the current. In that way, a signal can be seen on the collector or a signal can be developed on a base.

It may be that a more simple approach would be to use relays to control the entire cycle. One push button to start the sequence, it runs one time and stops until the button is pressed again. Is that what you really need?
 

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