8 replies to this topic

[The Swedish Scientist]

I was looking for a remote firing system, and was shocked when I saw the prices on these things.

The principle is very simple; a transmitter, a receiver and an amplifier. For the transmitter there are very many alternatives out on the market. For example circuits from ordinary RC toys could be used safely, as long as a few modifications are made. By adding an oscillator circuit and buttons to the transmitter and appropriate circuit wired to the receiver circuit should do.

Another alternative is a cell phone. By wiring a circuit to the loudspeaker's wires you could use the keys of any other phone to trigger the circuit. Using a walkie talkie is of corse also an option.

As for the amplifier, something reliable is needed. I think that something that does not trigger the output until the input reaches 2/3 of the power source. By connecting the amplifier's input to the ground via a resistance you'd avoid static buildup triggering the pyrotechnis.

Are there any blueprints available, or does anybody have ideas about how to build this?

[Richard H]

Do you not think that you are overlooking the safety implications of implementing a solution by the above?

[MFX]

I was looking for a remote firing system, and was shocked when I saw the prices on these things.

There's probably a good reason for the cost, engineering it safely, Liability Insurance, niche market etc. etc.

The principle is very simple; a transmitter, a receiver and an amplifier. For the transmitter there are very many alternatives out on the market. For example circuits from ordinary RC toys could be used safely, as long as a few modifications are made. By adding an oscillator circuit and buttons to the transmitter and appropriate circuit wired to the receiver circuit should do.

Hm using off the shelf RC gear is not to be recommended unless you know what you're doing most of this type of gear uses very simple coding and the recievers/transmitters are built for cost rather than quality.

Another alternative is a cell phone. By wiring a circuit to the loudspeaker's wires you could use the keys of any other phone to trigger the circuit. Using a walkie talkie is of corse also an option.

A CELLPHONE for setting off pyro !!!!!!!!!!!!!! I don't think so! (well OK there are ways it could be done safely but why would you want to !!!)

As for the amplifier, something reliable is needed. I think that something that does not trigger the output until the input reaches 2/3 of the power source. By connecting the amplifier's input to the ground via a resistance you'd avoid static buildup triggering the pyrotechnis.

Now you've really lost me!

Are there any blueprints available, or does anybody have ideas about how to build this?

Don't know about blueprints (If you can't design your own you shouldn't really be playing with this) but yes I have ideas as I build them professionally but sorry I not about to publish my designs. I you dont FULLY understand what your doing leave it to someone who does!

[pyromaniac303]

As for the amplifier, something reliable is needed. I think that something that does not trigger the output until the input reaches 2/3 of the power source. By connecting the amplifier's input to the ground via a resistance you'd avoid static buildup triggering the pyrotechnis.

Its fine preventing static buildup on the input, but if an object with any capacitance comes into contact with it (i.e. person, tree/plant, plastic bag blown by the wind, just about anything!) it will still apply a voltage until it is fully discharged.

You can buy small transmitter modules but these tend to work in the same band as garage doors and are subject to interference. If you come up with a really safe coding system that guarantees safety then they would be ideal. I've had a small radio module about 3 years now, only cost £10 back then, and im sure prices have reduced since then, but have been reluctant to put it to any pyro use.

Also the way you explain the above it seems like your planning to have a system where once anything is recieved, it triggers the ouput

The high cost is due to the testing needed to get a firing system approved, and that they are a fairly specialised item so therefore not suitable for mass production which would reduce costs.

[The Swedish Scientist]

A CELLPHONE for setting off pyro !!!!!!!!!!!!!! I don't think so! (well OK there are ways it could be done safely but why would you want to !!!)

Using a cell phone to set off pyro is the safest way, because there are no other radio transmitters that can interfere with the receiver. You can even block out all incoming calls but from the number you will be calling from.

Now you've really lost me!

If you don't know what an amplifier is, you really shouldn't say that on this forum. It is what amplifies the signal from the receiver into a current strong enough to set off the igniter.

As for the safety. By using multiple frequencies, like you get when pushing a key on your phone (not multiple carrier waves) you would get a safety level near what you have in remote triggers used for standard charges. The saftey on most pyro grade remotes is more basic than that. Usually the on/off switch is the entire saftey system.

I posted this thread to get new ideas about how to make this project come true. That is why I just gave the basics on constructing remotes instead of writing detailed instructions on how to build the kind of remotes I'm used to. I really don't think that a military engineer needs lecturing about safety and liability.

Edited by Eld i berget!, 26 May 2007 - 09:52 AM.

[MFX]

Using a cell phone to set off pyro is the safest way, because there are no other radio transmitters that can interfere with the receiver. You can even block out all incoming calls but from the number you will be calling from.

There are far better, cheaper and more reliable transmitters and receivers to use than cell phones. This is a forum for discussing display pyrotechnics and rocketry. The only occasions I can think of where someone might want to connect explosives to a cell phone are generally illegal and not for discussion here! Cell phone networks introduce unknown delays and dropouts which make them totally unsuitable for firing displays.

If you don't know what an amplifier is, you really shouldn't say that on this forum. It is what amplifies the signal from the receiver into a current strong enough to set off the igniter.

Of course I know what an amplifier is and yes there is one at the output stage of many firing systems (even a simple relay is technically an amplifier) however you wouldn't normally call it an amplifier in this case, generally it would be called a "switch" as it only has two states off and on. Amplifier implies something with multiple input levels and multiple output levels (e.g. A mosfet can be used as either an amplifier or a switch so it's fairly important to get the distinction right to avoid confusion). Where are you getting your figure of "2/3 the supply voltage" from? what defines that as "safe"? As it happens I have output stages that are switching 24 Volts from a 5 Volt input signal this doesn't conform to your 2/3 rule but is perfectly safe.

As for the safety. By using multiple frequencies, like you get when pushing a key on your phone (not multiple carrier waves) you would get a safety level near what you have in remote triggers used for standard charges.

If you mean DTMF, that is one signaling method yes, but it's not used in any commercial systems I know of for the simple reason that it's very slow. It can take up to 250ms to decode a single digit. Say for sake of argument you had a 16 digit security code, that would take 4 seconds to decode and that's without sending any actual firing information (which would also need to consist of multiple digits for safety). You can't simply rely on single DTMF digits for safety particularly as DTMF is an "open standard" i.e. anyone could be using it on any frequency for any purpose.

The safety on most pyro grade remotes is more basic than that. Usually the on/off switch is the entire safety system.

I think you'll find there's rather more than that going on behind the scenes! If there isn't then it shouldn't be used for pyro!

These are most of the things that need to be considered in a remote (and some wired) systems :-

Receiver end :-
On power on, test output switches (at this point the receiver must have disconnected the pyro from the output stage) If any are Live indicate a fault condition and prevent arming. This is more important than with wired systems as most wired field boxes are unpowered and hence safe until they get their power from the desk, however a wireless system must have a battery to operate so you don't want to turn on the receiver and have the display go off in your face!.

Also on power on check to see if valid information is being sent from the transmitter. If it is prevent arming and "go safe" because at this point the transmitter shouldn't be on because you've got the key round your neck (or in your pocket if you don't mind losing it on site ;-)!

Some people advocate a local arm switch with a "get away delay". Personally I'm not a fan of this and can see no real purpose for the delay, if it can go off unexpectedly while you're walking away then there is a major design problem somewhere! A two stage arming system is probably better, simply an arm key on the receiver which instructs it to wait for an arm signal from the desk. It could be argued that a separate arm key on the receiver is unnecessary as it can only be armed by a secure signal from the desk which we've already checked is switched off. But that's down to personal preference and many people like the comfort an arm key even if it isn't strictly needed! A nice bright arm led on the receiver that's visible from the firing position is recommended. The receiver should check periodically for valid data from the desk and if this is not received then it should disarm itself.

Transmitter end :-
On power on check to see if any of the firing buttons are faulty (stuck on) if so indicate a fault and either lockout that channel or refuse to arm completely. Also check to see if the arm key is on (it shouldn't be at initial power on) if so indicate a warning and remain un-armed until the arm key is switched off and back on again. When armed send periodic arm signals to the receiver (note it's VERY antisocial to constantly transmit as there may be other people on site using radio to control lights or sound, your system must be designed to operate in harmony with them and you shouldn't do anything that might screw up their systems, so only transmit when needed. It's also a good idea to have a "survey receiver" so you can check for problem signals and switch channels if needed.)

There are other complications such as do you go for a simplex or duplex system, remote continuity checking (needs a duplex system) etc. etc. Also some of the safety measures described can be left out or modified depending on what the system is actually going to be used for.

[dr thrust]

hi thinking about cheapo remotes can u not just use the guts out of a remote car and have the steering servo push a switch? keep it simple, and whats wrong with a long wire? ha ha

[MFX]

hi thinking about cheapo remotes can u not just use the guts out of a remote car and have the steering servo push a switch? keep it simple, and whats wrong with a long wire? ha ha

If you've ever done anything with radio control gear you'll know that servos can twitch at random for any number of reasons, also no security.

[dr thrust]

sorry about the , bad "idea" i will stick to long wires! and stop talking about things i know jack about, should of known better