233 replies to this topic

[Andrew]

The wafers used in logic chips are small, but every little helps. There is a much smaller amount of semiconductor in an SOT-23 package for example. Many people do not understand the economics, and no that doesn?t mean money! Copper will rise in value at least 10 fold within our lifetimes, perhaps even 100 fold, this is because it will soon be cheaper the recycle it rather than mine it due to dwindling deposits. Everyone bangs on about fuel cells and how they are going to give cheep and clean battery replacement. This is not the case, there are no known deposits of platinum and rhodium large enough to go around. We will have exhausted all the material in the earth?s crust long before we make enough fuel cells to go in all the mobile phones, let alone all the cars, base stations and other applications. Most people believe that hydroelectric dams are a very green way of producing electricity, it has recently been shown that a dam will produce more carbon emissions per unit of energy than a coal-fired plant will. That is why there is renewed political opposition to China?s proposed dams that will cover the area of the UK, not because of the displaced people.

As you said Alan, it?s not really that much of an issue how much silicon is used. No one gives a blind man?s binoculars about the amount of silicon, it is the second most abundant element in the Earth?s crust, and we will never run out of that. One of the largest issues is the energy consumed, but a larger issue is the waste and pollution. Thousands and thousands of tonnes of waste material is produced each year, hundreds of tonnes of solvent emissions are created each year.

[Andrew]

Damp test leads are not really an issue. Once you have injected enough charge into the line the entire line is of a higher potential. Once this has been achieved, the MOSFET?s gate leakage is the only current being drawn, this is typically nanoamps or less. One of the two resistors required limits the initial surge current into the line. The initial surge is due to the potential rising across the capacitance of the line and then the gate capacitance in the MOSFET. Technically you do not need any loop current to test for connectivity, just a small charge dump to cause the rise in potential that is seen at the other end.

My reason for suggesting using a MOSFET is safety. Most commercial ignitors have a guaranteed blow current of say 500mA. That means that some will blow on an order less than that. But to be conservative say 100mA. To have an acceptable margin of safety, you would want to have at least two orders less than that, perhaps even three. You want at least two orders below because one order is simply not good or safe enough. Say it takes 0.2 seconds to heat the ignitor so that it blows using 100mA. It would still blow on 10mA, but after around 3 or 4 seconds.

There will be a threshold where the heat energy produced by resistive heating, is transferred away at the same rate it is produced. To calculate this you need to know the resistance of the Ignitor Bridge, from this you can calculate the power that will be applied. You then need to know the volume of the bridge wire, and it?s specific heat capacity. Using these and the power you can work out the rate of temperature change. Then you need to know the thermal conductivity of the heat sink, i.e. the powder, and the thermal conductivity of the interface between the powder and the wire. With this and the previous calculation, you can calculate the threshold using a bit of calculus and an iterative solution. The threshold needs to be, as you can imagine, below the ignition temperature of the powder. But it also needs to be well below a temperature where the wire will start to corrode. When this happens, the resistance increases and the power dissipation goes up, thus it seems to gets hotter for no apparent reason.

Most home made ignitors will blow on 100mA or less. Ones that I have made before, from Stainless Steel wire from a 400# sieve and 60# to 80# grain powder, blow on 80mA instantly and even 10mA after a few seconds. If you apply a safety margin of just one order below this, your maximum test current you want to use is just 1mA. To light an LED, you want at least 5mA, usually more like 20mA. You are dicing with danger if you put a battery, the ignitor, a resistor and an LED in series. Using a bipolar transistor as a current amplifier is only just acceptable. On a cheep low power NPN transistor you would need a gate current of 200 micro Amps to drive an LED, which isn?t even two orders below the current what it can blow on after a few seconds.

From experience, if it has not blown after 10seconds your OK-ish. A MOSFET design would allow around 10 nano Amp of continuous loop current. And say for 200m of bell wire and a typical SOT-23 MOSFET, with a 1Mohm resistor, your maximum current will be 3 micro Amps, and it will fall to 10 nano Amps within a thousandth of a second. Well within anyone?s safety expectations. If you really wanted to be ultra safe, you could even charge the gate of the MOSFET prior to checking the line.

stay safe, also there is nothing more annoying than setting of fireworks out of the display.

[alany]

There is a much smaller amount of semiconductor in an SOT-23 package for example.

My understanding is that the die size is identical in most modern devices, SOT or DIP, or anything else.

Copper will rise in value at least 10 fold within our lifetimes, perhaps even 100 fold, this is because it will soon be cheaper the recycle it rather than mine it due to dwindling deposits. Everyone bangs on about fuel cells and how they are going to give cheep and clean battery replacement. This is not the case, there are no known deposits of platinum and rhodium large enough to go around.

Copper has always been rare, but I'd argue there is a lot of accessable Cu left in crustal rocks, and we are getting exceptionally good at working with poor quality ores. How much copper do we really need? Aluminium can replace it in power transmission lines, but for smaller electronics copper is much easier to work with. Refining either takes a hell of a lot of Faradays so I doubt one is really much better than the other Environmentally.

You can make fuel cells without Pt or Rh, they aren't as good, but organic polymers are getting better all the time. Fuel cells are a bit of a joke anyway, they are not very robust, so easy to poison and need very precise construction and exotic materials. Hydrocarbons are still the most practical fuel, we should concentrate on biodisel style schemes. Using carbon to carry around hydrogen is a heap easier than metal hydrides or cryogenics. Even exotic schemes like Boron burners need enhanced oxygen processing to work, methanol will burn nice a clean in a virtually unmodified internal combustion engine. Methanol even works in fuel cells with less exotic components. Biodisels burn great in gas turbines and can be cracked into just about anything, just like oil. The only problem is ponds of skum dry out easily and need lots of surface area, genetic engineering might offer enhanced photosynthesis in the future to help out. Photovoltaics are a joke long-term.

It is all a question of cheap energy, once you've got that pollution is a non-issue, you can easily reform wastes into useful or at least harmless stuff. Nuclear energy is by far the most practical source if the greenies really dislike releasing carbon into the atmosphere that much. Nuclear is quite expensive because of the cold-war fears that breed insanely excessive safety codes, but the basic technology is simple, cheap and exceptionally clean. There are fail-safe reactor designs available now, and nuclear electromechanical batteries look promising for cellphone/PDA use if the regulators would just get out of the way.

Anyway, back to the topic...

The problem I see with potentional driven devices like MOSFETs as continuity testers in a shooting circuit is they only need to have the gate charged to conduct. The time constant of the capacitance of a few hundred feet of wire and the gate insulation resistance is probably an hour or more! That's the only way you can achieve nA practically, any referencing to the rails to reduce the gate circuit capacitance problems will make it difficult to stay in the nA region with a reasonable time constant. With a bipolar device (or a LED) you need a real modest current to inject carriers, its a DC test not an AC one and the currents are large enough that the leakage capacitance of the line is no issue.

The no-fire current of commercial matches is usually at least 30 mA if not 50 or 100. LEDs glow plenty bright at 10 mA. If you look at my capacitive discharge box on my website (and posted in the "My System Worked" thread) you'll see that its testing current is 150 uA because it uses a neon as indicator element. At higher voltages gas discharge lamps become quite practical low-current indicator devices.

A couple of hundred uA is probably a good figure if you insist in complicating the continuity testing circuit. That is easy to achieve with bipolar or FET devices.

Edited by alany, 10 March 2005 - 04:50 PM.

[Andrew]

The problem I see with potentional driven devices like MOSFETs as continuity testers in a shooting circuit is they only need to have the gate charged to conduct.  The time constant of the capacitance of a few hundred feet of wire and the gate insulation resistance is probably an hour or more! 

Below is an acurate estimation to the rise/fall times. A thousandth of a second is a little bit shorter that one hour. The gate capacitance of a MOSFET is around 80 picofarads, You can charge the gate in a picoseconds if you want.

say for 200m of bell wire and a typical SOT-23 MOSFET, with a 1Mohm resistor, your maximum current will be 3 micro Amps, and it will fall to 10 nano Amps within a thousandth of a second.

[alany]

That's fine if the e-match is in fact good. What about if it isn't?

You'll have a large capacitance, perhaps several hundred nF in series with the gate resistance (and your 1M resistor). When the bridge is there the parallel wires in the shooting wire are shorted with about 1-3 Ohms, but when it isn't you have a large capacitor.

I can't be stuffed drawing the circuit, but it is just plain obvious that such a high-Z input will misbehave with a 200 ft floating antenna hung off it.

[Andrew]

You would probably add a resistor to have a weak pull down, I had thought of that and the noise potential. Anyway, "If it works it works". right!

[pyrotechnist]

Thanks for all the help guyes made a more electronic but basic fireing system that times out fireworks i am not going to use it it is just for my marks lol, i am going to get A+ for it .

[PyroKid]

Hi everyone,

I am looking to purchase an electronic firing system and am unsure as to what system to go for.

I currently have my eyes on either a 96 cue systsm from MLE Fire by wire, which will cost approximately ?600 for a 16 channel starter system or a PyroMate mini 96 firing system, which will come to approximately ?450 for a 12 channel starter system complete with internal 24 volt power supply.

The URL for the Pyro Mate system is as follows:

Pyromate Mini 96

I was wondering if anyone can give me some advice as to going about purchasing an electronic firing system such as any pointers on when to use electronic ignition over traditional hand - ignition ?

I understand that the use of electronic ignition can further broaden a pyrotechniciens level of creativity, however i am unsure whether to stick with hand ignition or to go electric.

I would also be greatful if you could view the above documentation and inform me as to what system would be more suitable?

[Richard H]

Why not build a DIY system? All you really need is a nailboard and a lead battery. Build a 96 channel system for probably less than ?30!

[PyroKid]

I had previously thought about doing something along the lines of this.
My only concern is that would such a system be acceptable in the firing of professional displays?

[Arthur Brown]

Creativity is in the MIND not in the tools. Design your show then work out how to do it, There are several ideas and circuits on here that will help you starting with the nail board and going right up to the sound-track on PC with all the cues back-timed to allow the burst to happen on the beat. Spend the money on fireworks, they are what the client sees!.

Rev Ron Lancaster states clearly that he started electric shows with a nail board, and his shows are OK!!!!!!!

Edited by Arthur Brown, 23 May 2005 - 11:01 AM.

[Richard H]

I can tell you now that large professional companies still make use of a nail board! How do you think that a large company might fire say 12 electrical shows on one night? I would doubt they buy 12 seperate pyromate etc systems.

[lodervsm]

Hi anybody has a nice fireing system circuit for me to build. I am in electronics therefore I can understand well
Bdw the most system that I liked using was the Fire One http://www.fireone.com/

I'd like to build a system like that since it costs many $$$


10x

[BurlHorse]

I can tell you now that large professional companies still make use of a nail board! How do you think that a large company might fire say 12 electrical shows on one night? I would doubt they buy 12 seperate pyromate etc systems.

I agree Richard, The only thing Lacking is Continuity testing, But if One pays close attention to the setup a nailboard is the best way to go.......additionally, there is a huge learning curve with the fireone system, I've been learning more every shoot from John Sagaria, But to get the cues right and learning the basics of timing shells and getting exact enough to have musical heartbeat hit right when the shell is a 1/3rd of the way open........really is rocket science!.

Best Regards,

Stay Green,

Bear

[KC Blast]

Hey everyone. This is my first post, since I didn't know where to begin I thought this looked like a good spot. Anyway, I just finished building a 20 cue firing panel that was on a user's website. I'm sure some of you know whom I'm talking about but since I don't know the "legallities" of posting of other's web sites I will omitt it for now. Anyway, I have a question regarding the wiring. Currently I have 100' of 22ga speaker wire. I was looking through fire fox's wire and saw that they had 24 AWG - THREE PAIR SHEATHED/COLOR CODED COMMUNICATION CABLE but dind't know if that would do me any good or not? I want to run 20 lines about 25 - 50' each. I thought that this type of wire would be easier since I can bundle them better. My firing system is powered by a 12v 7.5amp battery that I used to use for my astronomy telescope. Has anyone had any expereince with this type of wire or should I stick with the 22 ga speaker wire? Thank you everyone! Take care!

Eddie