Pyrotechnic Timing Device

[4pyros]

Hi;
I would like to make a timer for a DC motor driven pyrotechnic wheel.
It will be triggered from a pyrotechnic firing system at the right time in the show. The system has a 24 volt output of unknown polarity and will be lighting the pyrotechnic devices on the wheel.

After lighting the devices I need a short delay about 1/2 sec. Then I need to start the motor and a varible timer to shut the motor off after a 1/2 min. up to 2 mins.

I was thinking of sending the 24 volt fire power of unknown polarity to a bridge rectifier feeding an opto 4N35? then to a RC circuit that starts a 555 varible timer after the short delay. The 555 will power a relay that turns the motor on and off.
The hole thing will be running off a 6 or 12 volt battery.

Any other thoughts for the simplest way to get this done?
Would somone be willing to draw this up for me?

Thanks Andy

 

[alec_t]

(1) You could go solid-state and use a MOSFET instead of a relay.
(2) What current does the motor need at start-up?

 

[4pyros]

Thanks Alec; I thought of going with a SSR but the pyrotechnic wheel will only be used a few times a year and the use use of a SSR may not be justifyible. Maybe down the road, but right now we just want to see if this thing works and if its a crowd pleaser.
If you would like to look into it for me we will be using two car power window motors. Thay are 12 volts but we may run them at 6 volts. At 6 volts one that I pulled from a Dodge Ram was drawing 1.8 amps, may start at 10 or so amps I dont know.
We will run proto types for a year and then deside if it is worth it.
Andy

 

[KeepItSimpleStupid]

INMO, 555 timers are unreliable. I'd have to locate a kit for a timing module that works off of 12 V. There is a timer that I'm thinking about that might cost about $30 and has a relay output. Otherwise, look at timing relays from www.ssac.com. I'd say a ball-park price might be about $70.

If you don'e need much in terms of variable speed an AC synchronous motor could be used. It's not that hard to design a 12 VDC circuit to drive it at a variable speed. I've done it for a telescope for an acquaintance. He built it from my schematic.

In a final version this could be an embedded micro project. Just a thought.

 

[4pyros]

INMO, 555 timers are unreliable. I'd have to locate a kit for a timing module that works off of 12 V. There is a timer that I'm thinking about that might cost about $30 and has a relay output. Otherwise, look at timing relays from www.ssac.com. I'd say a ball-park price might be about $70.

If you don'e need much in terms of variable speed an AC synchronous motor could be used. It's not that hard to design a 12 VDC circuit to drive it at a variable speed. I've done it for a telescope for an acquaintance. He built it from my schematic.

In a final version this could be an embedded micro project. Just a thought.

Thanks for your input. But I think a 555 should be fine. It just needs to turn off sometime after the pyro is done. No presice timing needed. It needs to be simple and inexpensive.

Can anyone think of somthing simpler that will not cost alot?

Andy

 

[KeepItSimpleStupid]

I'm trying to find the timer that I think I might use, but here are two possibilities.

https://www.techtronics.com.au/p/108936/KITS_MISCELLANEOUS/NoBrand/K6140.asp

and

**broken link removed**

the manuafacturer's site didn't have any instruction manual.

So, you can get some almost ready made cheap solutions.

I'll keep looking for the other one.

 

[KeepItSimpleStupid]

Here is the timer I was thinking of:

https://www.electro-tech-online.com/custompdfs/2011/11/multimodetimer.pdf

 

[alec_t]

Can anyone think of somthing simpler that will not cost alot?

How about this? Cheap as chips. Timing won't be very precise (but you said you don't need that) and it can be built for just 2 or 3 $$. The components aren't critical and the MOSFET should be ok without a heatsink if a low Ron type is used. R1*C1 determines the start-up delay and R2*C2 determines the motor 'on' time.

 

[4pyros]

Here is the timer I was thinking of:

https://www.electro-tech-online.com/custompdfs/2011/11/multimodetimer-1.pdf

Thats nice but whare can I buy it?

 

[4pyros]

How about this? Cheap as chips. Timing won't be very precise (but you said you don't need that) and it can be built for just 2 or 3 $$. The components aren't critical and the MOSFET should be ok without a heatsink if a low Ron type is used. R1*C1 determines the start-up delay and R2*C2 determines the motor 'on' time.

OK do you think I can get a minute out of the R2-C2 combonashoin?
Could I do the timing with transistors and R-C combos instead of the chip?

 

[mbarazeen]

you can do it with 555, just trigger a latch by a limitted (can use a zener) direct input after rectifying the unknown polarity. make a RC delay for 1/2 sec & trigger a monastable 555 to give you adjustable off time. either you can reset your latch when 555 returns (off) or it can be reset manually by a micro switch... you can skip the latch if the system gives a long duration signal.

 

[alec_t]

OK do you think I can get a minute out of the R2-C2 combonashoin?

Easy. In a simulation the component values shown for R2 and C2 give a run time of ~90 secs. Just increase R2 and/or C2 for longer.

Could I do the timing with transistors and R-C combos instead of the chip?

That would be tricky with bipolar transistors, because they need significant base current which means much bigger capacitors. Why not use one CD4093B chip? It runs on nano/microamps, costs only a few cents and contains all three gates for the suggested circuit !!

 

[4pyros]

you can do it with 555, just trigger a latch by a limitted (can use a zener) direct input after rectifying the unknown polarity. make a RC delay for 1/2 sec & trigger a monastable 555 to give you adjustable off time. either you can reset your latch when 555 returns (off) or it can be reset manually by a micro switch... you can skip the latch if the system gives a long duration signal.

opps, The fire signal is a short pulse, so a RC combo before the timer would not work. It would hve to latch.

 

[4pyros]

That would be tricky with bipolar transistors, because they need significant base current which means much bigger capacitors. Why not use one CD4093B chip? It runs on nano/microamps, costs only a few cents and contains all three gates for the suggested circuit !!

I was just wondering.
The other side of the story is I would like to proto type it with parts I have on hand. I dont have any 4093s but I do have 555s, transistors, and relays.

 

[alec_t]

Ok, back to the drawing board.

The fire signal is a short pulse

Can you be more specific? Polarity? Duration? Magnitude?

I would like to proto type it with parts I have on hand

Sounds like me!

 

[4pyros]

Ok, back to the drawing board.
Can you be more specific? Polarity? Duration? Magnitude?
Sounds like me!

The output of the firring system is 24 volts of unknown polarity for long enough to fire an e-match, 1/2 a sec. or so. I would like to run this off other firring systems as well, some what universal.
The voltages can vary from 9 to 36 volts at differant pules lenghts. I don't know exactly how long but I can find out.
I know I may not be able to run the hole range but as much as posible would be nice.
Andy

 

[alec_t]

How about this then? Simulation gives a 1/2 sec delay then a 2 min 'on' period with the components shown. The opto gets 10mA with a 24V firing pulse (I haven't checked what it should be for a 2N35). Increase/decrease its series resistor for use with greater/lesser pulse voltages if necessary, to stay below its specified current max.

 

[KeepItSimpleStupid]

9 to 36 V we can deal with. I know a nice circuit that will work for 3 to 30. It can be modified slightly.

 

[4pyros]

9 to 36 V we can deal with. I know a nice circuit that will work for 3 to 30. It can be modified slightly.

Sounds good can we see it?

 

[4pyros]

How about this then? Simulation gives a 1/2 sec delay then a 2 min 'on' period with the components shown. The opto gets 10mA with a 24V firing pulse (I haven't checked what it should be for a 2N35). Increase/decrease its series resistor for use with greater/lesser pulse voltages if necessary, to stay below its specified current max.

Thanks alec; I will try it soon.