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What I want to do...

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TCLynx

New Member
I want to make a controller that can trigger a linear actuator. The actuator needs about a .2 second pulse. 12 vdc pulse to extend and -12 vdc to retract.
I would like to have the controller repeat the cycle as long as it has power and to reset and start over when power is applied.
positive pulse then wait a period of time then negative pulse and wait a different period of time repeat as long as power in applied. I would like the time periods to be adjustable from around one minute up to about an hour but the adjustment doesn't need to be very fine. (I can work out adjustments on a bread board before I lock in what ever is best or I could set up dip switches if I want to keep it adjustable.)

Anyway, that is essentially what I want to do. What should I be searching for when I go looking for plans, tutorials, schematics and such to do this? I've been trying to search but I don't know the best terms to use and therefore am spending days wading through totally unrelated links.

It is kinda like a repeat cycle timer but with the twist of needing to set a positive pulse then a negative pulse and the time periods will need to be different. Unfortunately, I don't have a pic programmer and don't want to spend a huge amount of money on this project.

Please aim me in the right general direction. I'm getting sick of needing to manually flip the switch up and down all the time. This would really like to be automated.
 

Mr RB

Well-Known Member
Sounds like you have 3 separate timed periods;
1. +on -on (same time 0.2 sec)
2. adjustable pause after +on
3. adjustable pause after -on

I would use a DPDT reversing relay to simplify the +/- 12v part. Then to do the time delays without a PIC...

555 timers etc will struggle to do an hour.

Maybe you could use something like an 8bit CMOS binary counter IC do do the sequencing. A 555 timer to clock the counter. Another 555 to generate the 0.2 sec which I'm sure needs to be fine tuned. And some simple logic gates from the binary counter to sequence the +12v cycle and the -12v cycle.

It really would be so much easier with a PIC. :)
 
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TCLynx

New Member
Ok, then for that I think I found some one to help me out with a pic and a kit. Will likely be several weeks till that happens though. Sigh.
 

TCLynx

New Member
If you say what the secret device does... Then people might offer more suggestions on an easy way you can make it work!
:)
I'm using a two wire car door actuator to open and close a low pressure valve.

It needs a .2 second 12 vdc positive pulse to move the actuator one way and a .2 second 12 vdc negative pulse to move it the other way.

I want to be able to open the valve
wait a period of time
close the valve
wait a period of time
open the valve and so on..............repeating.
 

Mr RB

Well-Known Member
See? That's really helpful. You can get car door lock actuators that have end of travel limit switches built in. There is usually one of that type in each set of 4 actuators (that also controls the other 3).

So you don't need to time the power to the actuator, you just connect it to +12v and it operates, and it's limit switch cuts the power.

And 40 mins later you connect it to -12v and it moves the other way, then that limit switch cuts off.

You just need a 555 timer to operate a reversing relay (DPDT) to send +12v or -12v to your actuator. The end of travel limit switches have diodes across them (or you can add a diode to each switch) so that when they cut the power it still allows the reverse power. That's generally how they are wired in the car anyway.

You whole project just got real easy.
 

TCLynx

New Member
trick is, I already have the actuator and there is no limit switch. It is a two wire actuator.

I wasn't really planning to buy a whole 4 door kit with controller for this project.
 

TCLynx

New Member
It seems to me as though this could be managed like a couple of delay timers though.

When power comes on, one of the delay timers gives out a + pulse and the second delay timer waits a longer period before giving a - pulse. I just need to figure out how to wire it up so the one set of wiring doesn't cause issues with the other set. (I believe this can be done relatively simply, I'm just not well enough versed with electronics to be able to work all of it out myself with no help.)
 

Sceadwian

Banned
Will the device you're using be damage if the linear actuate extends too far, or retracts too far? Without feedback if you don't get the timing right you'll either damage your setup, or not extend/retract far enough, limit switches would be far simpler and easier to implement.
 

TCLynx

New Member
The only danger is if the device is energized for too long, it will heat up and quit working. I believe .2 seconds is how long it needs to reach full extension. I've not burned one up when using a momentary switch on it even when I know I've held the switch for a full second. The situation does not require super accuracy, just short enough to avoid melting down the motor.

I've managed to hook up a little timer that when I supply power, the 555 will deliver a short pulse so I've manage to get one half of the function working.

Now I just need to work out how to wire up another little timer that will wait for a while before delivering it's pulse. This should be pretty easy if I have enough parts for it.

Finally I have to figure out how to have these two timers operate something like an H-bridge or a few relays so that the one gives the positive pulse and the other gives the reverse polarity pulse.

Then I can hook the whole thing to a 15 minute on, 15 minute off mechanical timer and I will have something that can close my valve for 10-15 minutes every half hour.
 

TCLynx

New Member
A PTC fuse / resistor should do the trick.
Which bit would this do the trick for?

I have the initial pulse sorted out with a 555 circuit.

I'm working on the delay before pulse timer now.

I was thinking that perhaps a DPDT relay could take care of the H-bridge part of it.

If some one has an idea of how to diagram how I should wire it all together and hook up the relay to be able to reverse the polarity to the actuator, I would love to see how that should be drawn. I'm trying to figure out how best to diagram what I've done so far and what I plan to do in a way I could post here, but I don't really want to spend 48 hours messing with that when I have plenty of other things I should be doing.
 

TCLynx

New Member
A PTC fuse / resistor should do the trick.
Still at a loss here, how would a resettable fuse help me in this situation?

Also, I've been searching and searching but not having much luck finding examples of circuits to help me in my tinkering. I've been successful at making an adjustable interval timer and used the knowledge I gained from that kit to successfully make a one shot pulse that happens almost as soon as power is applied.
Yay, that is step one.

Still searching for a way (and this all needs to be when power is applied since I can't hang around 24 hours a day to push a button)
A way to have a delay before a second pulse is triggered. I'm thinking this needs to be some circuit with perhaps two 555 chips (I have like 4 or 5 of these things around)(I also have a couple 14 stage ripple counters, a dual D type flip flop, a mc14093bcp though I don't know what use that will be for this, and a LM324N though I couldn't even manage to download the data sheet for that.)

I've found some reference about using one 555 timer to trigger another but it talks about AC coupling and I don't really understand what that means and looking it up on google didn't really help me much (sorry, I do have a headach at the moment so it is making me a bit impatient with searches that return oodles of completely non related matches.) Could some one give an explanation about how this AC coupling is done to make one 555 able to trigger a second one?

Finally, I've picked up an assortment of DPDT relays. I'm wondering how best to wire them up to achieve the polarity swap first pulse positive from the initial one shot and second pulse negative from the delayed one shot.
I had figured this part would be easy after I had managed to wire up a switch for triggering the actuator but I guess that is just because I managed to find the right switch for the job- It happened to be a momentary center off DPDT switch so it was pretty easy to wire so pushing the switch one way would actuate up and pushing the switch the other would actuate down.
Any tips here would help me loads.

Thanks, now I think the headach is gonna put me to bed.
 

KMoffett

Well-Known Member
This link is for a recycling, 3-stage 555 monostable circuit. By add in another stage, I think you will get the sequence you want: Fwd...delay...Rev...delay...Fwd...delay........

LM555 Timer Circuits

The attached is for a relay H-bridge. One relay coil would be connected to the output of the first 555. The other relay coil would be connected to the output of the third 555.

But, like everyone has said, a timed auto-reversing actuator, without limit switches or over-run detection, will eventually creep in one direction or the other and jam.

Ken
 

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Mr RB

Well-Known Member
Those door lock actuators are pretty tolerant. They use a little "toy style" DC motor but a 12 volt low current version, and strong gearing and mechanicals that are not damaged when they hit the end stops at full power. And the motor has a fairly low stall current, they are quite tolerant of stalls at least for short periods.

They are quite low force actuators though... It might not be enough to operate a rotary valve reliably.
 

TCLynx

New Member
Those door lock actuators are pretty tolerant. They use a little "toy style" DC motor but a 12 volt low current version, and strong gearing and mechanicals that are not damaged when they hit the end stops at full power. And the motor has a fairly low stall current, they are quite tolerant of stalls at least for short periods.

They are quite low force actuators though... It might not be enough to operate a rotary valve reliably.
No they definitely would not operate a rotary valve. It is really only lifting and lowering a flapper type backwater valve that is placed in line backwards. So the water pressure actually keeps the valve in the closed position and a spring helps keep it in the open position. The actuator just assists in changing the position.

Anyway, got ahold of a friend that used to dabble in electronics. Went over to his place the other day with the junk I've collected and we went through his junk drawer. He came up with something for me to build and I've got it out running the valve.

It consists of a 555 repeat cycle timer controlling the coil on a DPDT relay.
The output of the 555 timer is also going to a couple circuits on a 4093 chip which has some little Resistor/capacitor timer circuits hooked up to control the pulse length and the output of that goes to a 4071 chip which is driving through a 680 K ohm resistor to a Transistor who's output is controling the coil on a SPST relay.

So, the SPST relay contacts control the path to ground for the motor power and is connected to one of the NC contacts on the DPDT relay and to the diagonally opposite NO contact. The positive power for the motor connects to the other contacts on the DPDT relay and the motor is run from that DPDT relay and though I don't entirely understand the 4093 and 4071 chips so well, the circuit is built. I tinkered around with resistor and capacitor values till I got the time range that will work for the purposes and it is out running a valve on the Aquaponics system as I sit here typing.

I would post a diagram but at the moment my scanner is refusing to speak with my computer and I got too much other stuff to do so I can't look into it at the moment. Perhaps I'll take a photo of the diagram and circuit later but kinda busy after having to replace my well pump and all the wiring to it the other day.
 
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