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Help with a three-way switching system

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Hi all,

First of all I should make clear that I am relatively new to this so please bear with me.

I'm trying to design a circuit which has 3 'push-to-make' switches all linked to the one solenoid. I would like the solenoid to run for a set amount of time and then turn off - even if the switch is still in the 'on' position. The time should vary depending on which switch is pressed.

I am having trouble getting my head around this - I am pretty sure it will require the use of a capacitor and various resistors to determine the different amounts of time the solenoid will stay on but I'm not sure how to approach it.

Once I've figured out the basics of this circuit I would maybe like to add an LED which will come on when a button is pressed and stay on for a duration after released.

If anyone could point me in the right direction I would be grateful.

Thanks,

Stuart
 
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First of all, you'll need three separate monostable triggers. I've a link here that describes a monostable circuit with the 555 timer. I haven't checked what happens if you click two or more times on trigger-button rapidly.

To prevent trigger pulse being longer than just a very short pulse, you could always do the NAND/AND with a inverter on one input (atachment).

You haven't told what should happens if two triggers being activated simultaneously (or wery close at same time).
 

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First of all, thanks for replying. I hadn't said what should happen when switches are pressed simultaneously because I hadn't even thought about it. :eek:

I'll spend some time familiarising myself with the link that you provided. It will probably take me some time to get my head around all of this - I am doing it strictly as a hobby.

When I get to the stage of drawing up a schematic I will post it here and you can point out all of my amateur mistakes.

Thanks again.
 
Ok, I've been spending whatever free time I've had reading up on 555 timers and such. It's going pretty slow as I am a complete beginner at this and I don't have much free time anyway.

I've come up with a schematic which suits my needs - as far as I can tell - but I still have a few questions. Have a look at the attached image.

The circuit itself consists of 3 buttons which light the first set of LEDs for a different amount of time each, the second set should come on simultaneously and remain on for approx. 30 seconds.

When getting to grips with the schematic, for simplicity I left out the solenoid (it's actually a solenoid valve) I originally wanted. I would like to add the solenoid in series with the first 2 LEDs which will run for the same time as them. Can I simply add that in or will I have to go back to the drawing board?

I have not even looked at solenoid valves to buy - will the type of solenoid I use greatly affect my design (supply voltage/resistors/etc)?

The timings for each button are just estimates so that I could visualise the process - I still have to work out the exact values of my resistors/capacitors. Have I made this more complicated than it has to be? Do I have anything where it shouldn't be?

I am trying my best but I am beginning to feel a little out of my depth. It's time to consult more experienced people than me.

There is one more stage to the circuit which I will add once I am completely comfortable with the current stage. Any help is much appreciated. Feel free to give suggestions - I am not looking for someone to do this for me, but another point in the right direction would be great.

Thanks.
 

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Timers

How about a picture to get us all on the same page.
Here is a circuit with 3 different timers.
You can push and hold and they will time out.
They ar "OR'ed" together so 1 or 2 or 3 will energize the solenoid.
If 2 are pressed at the same time the longest will "win".
Plots are input (switch), output of that timer, and out to solenoid/led.
 

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There is a picture attached to my last post in PNG format - I have re-attached it as a GIF in case there was an issue with the format.

It's a different set up from the one you posted but I think the general idea is the same - although I am a complete novice so if I have done something ridiculous I wouldn't know.
 

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Almost the same thing. There are a couple of "buglets":
The logic gates will need another supply. If you go this way use the 400X family instead of the 74SXX so you can run them off the 12 volts.
The pulse generated by the 74s04 and the and gate will only be a propagation delay wide (10 ns.) which is not long enough to be a good trigger for the 556's. You could use the RC with diode clamp like the other circuit or stretch the pulse with an RC.
The first 2N1711 needs a resistor base to emitter to turn it off because the diodes block the input in the negitive direction.
The base resistor could be a little smaller to ensure the transistor is saturated. Usually a gain of 10 is used. So if you want 12 ma at the output you should have 1.2 ma at the input.
I would move the LEDs to the collector side so the trigger signal has the full voltage swing instead of being two drops above ground. It will work the way it is but will have more noise margin the other way.
You can remove the 9K.
You can remove the 1N4001 from the base of the second 2N1711 or add a base emitter resistor like the other one.
Need to add a 1k to limit the LED current in the second circuit.
If the timing tolerance isn't important we could make a simple one with just logic gates. Does it matter if the timing is 1 second or 2 seconds?
 
Thank you for your reply - I have taken your advice with everything I could.

The logic gates will need another supply. If you go this way use the 400X family instead of the 74SXX so you can run them off the 12 volts.
I am using the trial version of multisim and I could not find any other family of NOT gates- I only seem to have the 74sxx in my database. I replaced them with the generic NOT gate for now and will keep what you said in mind when/if I manage to start building this.

The pulse generated by the 74s04 and the and gate will only be a propagation delay wide (10 ns.) which is not long enough to be a good trigger for the 556's. You could use the RC with diode clamp like the other circuit or stretch the pulse with an RC.
Are you saying that in reality the circuit would not work as the pulses generated would be too short? I have not had time to look into this just yet but I will read up on the RC and diode clamp - thanks for the advice.

If the timing tolerance isn't important we could make a simple one with just logic gates.
Unfortunately the timing is the most important part of the circuit. I know that the 555 timers may not be wholly accurate (depending on the capacitors?) but as I mentioned before I plan on adding a small solenoid valve in with the first set of LEDs and hope to set it to release three reasonably accurate amounts of liquid based on the timing (when I work out the exact values of my resistors and capacitors).

I have taken on board everything else that you have advised. However, when I added a 1k resistor to the second LEDs they failed to turn on - I have added a 500Ω resistor instead. This was based on the maximum resistor that would allow the LEDs to function in the multisim simulation.

I have added an image of my up to date schematic.

I just want to say thanks again for your help and advice - I really appreciate the support I have received in trying to learn something new.
 

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3 way

Oooppps, my bad. The LEDS should be in series to work the best. If the forward voltage drop from one to the other is much different one may "steal" all the current and the other not turn on. So if they have say 2 volts drop at 20 ma you could put them in series and use a 400 ohm (390).
Here is a picture of the RC network.
 

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