Sequential delay Circuit

[snooprob]

All,

I am a general novice working through a design for a circuit to use in my home theater rack. I would like the 12v out from my pro-processor to to turn on 5 amplifiers one second apart. It seems I am doing pretty well on the bread board with christmas lights as dummy loads but my primary problem seems to be turning them off.

So what happens thus far.. i have power applied to circuit and all loads are off. When i apply 12v to the input phototransistor (right name?) the loads turn on one second apart. All is well, except how to I get things to turn off? Seems the 555 timers are one shot (monstable?). Do i have to use the reset pin or something? How can i do that when the 12v input goes away (but not the 12v circuit supply).

Right now only way to turn everything off is remove the 12v circuit supply (bench power supply). Insight on my approach would be appreciated!

Thanks.

**broken link removed**

 

[Mike_2545]

I don't have that answer for you but one thing crossed my mind when seeing the triacs. What sort of wave pattern are you going to be feeding your home theater? Some of that stuff only likes pure sine wave. It may be better to consider relays, or at least driving relays with the triacs.

 

[MrDEB]

One problem is the 555 circuits

they are not configured as one shots
To have each triac come on one second apart then all shut off at same time is pretty easy is my first thought.
A 4017 as a count to N (5 triacs so N=5) is my first idea but need to work on it.
D flip flops might even work??

 

[ccurtis]

To turn the whole shebang off, connect a switch across U1's diode.

Of course, the caps will take a while to discharge. So, better yet, connect one end of three resistors to the top of the caps, connect the other ends together to a switch to ground.

 

[snooprob]

Curtis : power to u1 goes away when reciever is off (on the left side, not the right).. but the 555's continue to pull pin3 to ground keeping the triacs on. I would prefer not to have an additional switch involved.

MrDeb : sorry but i didn't follow you at all. Some sort of logic gate??

Mike2545 : do triacs mess up the power signal? I probably don't want that as it would probably make noise. Good to know.. i might have to switch to relays if that is the case. Still have my 'turn off' problem.

Thanks for the thoughts all. Keep 'em coming.

 

[Mike_2545]

Mike2545 : do triacs mess up the power signal? I probably don't want that as it would probably make noise. Good to know.. i might have to switch to relays if that is the case. Still have my 'turn off' problem.

Yeah, they make a saw tooth wave if memory serves me correctly.
That why you don't put your stereo on a dimmer to adjust the volume.

 

[ccurtis]

I would prefer not to have an additional switch involved.

What did you have in mind to determine when to power down the three units you are sequencing without shutting off the power?

 

[ccurtis]

Oh, I think you mean you want to turn the proprocessor off and leave the other +12 volts on. Your schematic does not make a distinction between the proprocessor power and the other +12 volts, so they look like they comes from the same source.

 

[snooprob]

ccurtis: Yup the +12v are different sources. The receiver is only good for like 20ma or something. Trying to isolate it from the circuit as well so if i jack something up i don't wreck my reciever

 

[snooprob]

Mike: Again I am a noob, but please bear with me. For the triac if I am doing off/on and no in-between PWM where i would expect a sawtooth do you think the output will still be non-60hz smooth sine wave? I don't have a scope and google was surprisingly ineffective turning up details - most applications are dimming as you noted.. other than 'large' SSD's for motor relay type work. Thanks!

 

[Mike_2545]

Yeah, It definitely changes the wave form. Inductors, lights and things of that nature don't care but its like vinegar in the milk to computers & stereos. I've got one here on the bench, I'll give it a test and see if my memory is any good.

 

[ccurtis]

Okay, how's this. Connect a diode across each of R3, R11, and R10, with anode toward the capacitor. Connect a resistor from the emitter of Q1 to ground to bleed off the capacitors when Q1 turns off.

 

[Mike_2545]

snooprob,

I have a MOC3011 optocoupler driving a 2N6073a triac full on. this is turning on a relay. Here is a picture of the scope.

As you can see not pure sine but not as bad as I remember either. I would still operate off relays.

 

[Mike_2545]

Another reason to go with relays is that you need to design a triac circuit for either resistive or inductive load. You may have a mixture in stereo equipment but I suspect that it is mainly inductive.

Relays all the way...

Oh and you will need to redesign the triacs you have to run relays. I have a reference book if you want to go that route. You may want to drive a transistor to turn on a low voltage coil relays.

 

[snooprob]

Mike: thanks for the quick benchwork - greatly appreciated! I'll probably ditch the triacs and run relays right off the 555 .. seen plenty of schematics on how to do that. Need to order some relays though, don't have any on hand.

Ccurtis: I'll give the diode approach a shot tomorrow when i get a chance. Thanks for the recommendation. It is entirely possible i was just not patient enough for the capacitors to run off their charge .. assuming it would "never" turn off

Thanks again to the both of you for your prompt replies. And of course if you see an easier approach overall than the one I am taking let me know!

 

[ccurtis]

It is entirely possible i was just not patient enough for the capacitors to run off their charge .. assuming it would "never" turn off

It is guaranteed to turn off without any modifications. U2, U6, and U7 will be pretty quickly starved of power once the capacitors discharge enough. The capacitors won't completely discharge though for quite a long while after that, affecting your power-up sequencing time when you turn on the pro-processor again.

 

[Mike_2545]

Mike: thanks for the quick benchwork

Just tell me where to send the bill...

 

[ccurtis]

And of course if you see an easier approach overall than the one I am taking let me know!

There is likely an easier approach overall, but you already went through the work of constucting what you have, so it seems to me that a modification is the better route.

 

[MrDEB]

This is what I had in mind

I don't see how your circuit goes in sequence?? I am missing something??
the attached is just what I was thinking. needs lots of work - rest set pins, transistor resistors etc.
the 555 is configured to pulse every 1 second. when the count reaches X then disable the clock inputs and reset the D flip flops and all the relays shut off all at once (the Q outputs go low)
I know it looks unprofessional but its just a start.
how long do you want the amps on after the 1 second ON event??

 

[snooprob]

ccurtis : the diode/resistor modification did the trick. I did a 1k to ground and the 555's output goes back high after about 1 second. Seems i am good to go!

mrdeb : the 555 has 1k extra resistance in the r/c circuit than the one above it adding a second (or so) before changing the output to low turning on the load (amp in my case). Theory is when my receiver is turned on.. the 12v trigger output through phototransistoer (right name?) sets things on motion and my amps will turn on sequentially. They should stay on until the 12v source goes away and ccurtis' addition drains the caps and they turn off. Thanks a lot for taking the time to offer an alternate (and probably better) design.. but this one is now working and i understand it!

I'll post pics of the completed contraption after i get relays. Assuming it works of course! Thanks all.