Continuity tester

[FrankRizzo]

The shunt wire is not an issue. The main filament is fairly low resistance (~2.2 ohms in the brand I use), and the shunt is an order of magnitude larger. As long as your current limiting resistor is sized correctly to allow just the bare minimum amount of current necessary to light an LED, the extra resistance offered by the shunt will limit the current to a point where the LED does not light.

[patsroom]

" At that point, heat caused by current flowing through the shunt burns off the coating and reduces the shunt's resistance. (A typical bulb has a resistance of 7 to 8 ohms through the filament and 2 to 3 ohms through the shunt once the coating burns off.) "

 

This is of course is a qoute from the site:

http://tlc.howstuffw...mas-lights1.htm

Reading this external link will save some question as to why the Christmas-bulbs work and why the shunt does not interfer with what we are using it for.

It is possible that the shunt could be activated during the firing of the ignition, but in most cases I do not think that there is enought volts and amps maintaining the circuit through the shunt to do this. I am not saying that it can not happen, but the likley hood of it occuring is very low.

 

I personnally can say that I have never had a problem using Christmas-bulbs as igniters.

 

I would love to hear from others that have used Christmas-bulbs as igniters and what they did to prepare them in making igniters from them.

As for myself I just break the glass tip ensure that the BP is in contact with the filament and use as is with a 12 volt car battery most of the time.

[Updup]

I would love to hear from others that have used Christmas-bulbs as igniters and what they did to prepare them in making igniters from them.

As for myself I just break the glass tip ensure that the BP is in contact with the filament and use as is with a 12 volt car battery most of the time.

 

Take A look at the X-mas light igniter thread in the members TUT section... Some people had some interesting stuff/methods to share there.

[patsroom]

Updup Thanks for the lead. I will have a quick look over there a see what others have done......Thanks again..............Pat

[Updup]

Updup Thanks for the lead. I will have a quick look over there a see what others have done......Thanks again..............Pat

 

Anytime.

 

I tested some of my E-matches from last year, and a few didnt work, I'm thinking if I diped and sealed my matchs the filament would hold up better

[dave321]

I found the original files back, including the PCB design. It uses a red/green dual LED with common cathode. When red, the igniter has been fired or isn't working properly. When green, the igniter is conducting. Probably way too fancy for most of us, but heck it looks cool.

 

Schematic.pdf

Silkscreen.pdf

Transfer.pdf

 

I later added a 10k resistor between pin 3 of the opamp and the V+ connection. This prevents your opamp from hitting the rails, prolonging its life expectance significantly.

 

For members knowing how to use Cadsoft Eagle, I got the files attached below.

 

FiringBox_.zip

re the schematic pdf, what are the 3 items in the top right hand of the drawing ?

are they part of the actual testing circuit or the firing side of things ?

 

forgive me I am no electronics guru.

 

on a separate note why would a tester like :-

http://www.wizard-devices.com/dsl.shtml

 

cost $60 ???

when its probably just got one resistor in it limiting the current to a safe level

[deer]

Besides just limited current, I'd like to point out, that safe continuity tester would limit total power delivered to igniter in all ways - current, maximum voltage and use of very short pulses.

 

You could design something like that using digital logic, that latches the led on and cuts off current to igniter as soon as continuity is detected.

 

Otherwise with e.g. 100ohm igniter, even if you limit the current to, say 5mA, but deliver e.g. 24V - that's 0.12W which is basically enough to overload a surface mount resistor. Keep it encased and overloaded for long enough and it'll burn. If you limit both, voltage and current (e.g. 5mA @ 3V), you'll never go past 0.025W and are less likely to cause voltage related effects (material breakdowns etc).

 

Even when using multimeter, make sure it measures resistance with low current. Be especially careful with analogue ones.

Edited April 17, 2015 by deer

[50AE]

Modern LEDs are so sensitive! My own continuity tester is designed at 4mA of test current, but still glows a bit when I close the circuit through my body by pressing both hands on the terminals. If there is a microamp leakage current somewhere, especially in whet/damp condition, the tester detects them and confuses my colleagues.

Edited December 15, 2015 by 50AE

[Arthur]

In real firework conditions (on wet ground ) it's easy to get false continuity through a drop of water in a connector.

[lloyd]

There might be a chance that you could burn through the oxide and make the final connection of the shunt. But I think that we push the voltage at a lower requirement and for a very short time that the shunt lacks the current needed for the connection to by pass the destroyed filament.

-------------

That shunt wire is almost "magic". As supposed, there is an oxide layer on the wire that prevents contact from being made at the low voltage (typically 3-6VAC) at which each bulb operates.

 

If any bulb opens, though, suddenly the voltage across that one bulb rises to 120VAC, arcing through the oxide, and forming a weldment between the filament risers and the shunt.

 

And the voltage on all the other bulbs in the string now rises by their 'share' of the now-shorted bulb's supply. So, if there were - say - 20 bulbs in a normal string, each would normally be operating at 6VAC. Short one out. Now there are 19 bulbs operating at 120VAC, so each gets 6.316 volts. That's why it's good practice to replace a burnt-out bulb as soon as you notice it.

 

They really make very BAD electric matches. You'd be far better off to buy bare match heads from someone like ODA, and dip your own.

 

Lloyd

[BaxieBull]

What are the specifications of this continuity tester?

What is the priciple behind it? Does it use any induction method or any other method?

Also what are the details of the all of the hardware components?

[lloyd]

I've been reading this with a little (non-insulting) amusement. Before starting my pyro career, I was an EE. This made the conversation interesting for me.

 

An e-match continuity checker is a simple thing (schematically), and can be safe while not giving any 'false continuity' results.

 

Unless your environment, matches, and the checker are filthy with combustion debris from prior shots, there's no way a properly designed checker would give a false-positive due to hands touching the electrodes or a droplet of water across the leads. Although mineral-content water is slightly conductive, it nowhere near represents the low resistance that a match would.

 

A checker must be designed with a particular match (or at least 'style' of match) in mind. One checker will not properly inspect MJG matches and home-made ones made from busted-up Christmas tree lights. The maximum 'safe' current of the match must be known prior to designing (maximum no-fire current), and the circuit should be designed to never put more than 25%-50% of the safe current through a match.

 

Further, it must be robustly built from components that cannot fail from mishandling or testing shorted leads. Otherwise, the max-safe specification might be exceeded due to a mechanical or electronic failure.

 

The simplest circuit is simply a relatively high internal resistance battery in series with a resistor that positively prevents more than that safe-range current to flow through the LED. However, that three-component tester won't prevent a good LED from glowing a little with a high-resistance across the test leads. For that, we need a little more 'processing' in the tester.

 

An inexpensive Norton amplifier along with a couple of resistors to form a voltage reference comes to the rescue. Then, instead of directly measuring the current through the match, we can measure (and compare) the voltage across the match to the reference voltage. With that scheme, there are no 'false positives'.

 

We can even take that a bit further, and make the tester see a 'window' of voltages, so that it will flag a short as well as a good match.

 

When MJG was making a LOT of shorted and open matches shortly after they moved production to Mexico, we had to make up such testers to identify both conditions. It was - in essence - a 'digital' version of a Wheatstone Bridge, but instead of a "null meter" it lighted lights to indicate either good or shorted conditions.

 

The design is proprietary to my past employer, so I can't share the schematic, but with the info above, any competent tech could whip up an equivalent in an hour or so.

 

Lloyd

Edited December 15, 2015 by lloyd

[MadMat]

Lloyd,

If I get it right, you are basically creating a wheatstone bridge (voltage dividing resistors)

with the norton amp hooked up as a voltage comparator... right?

[lloyd]

Correct. I went a step further and used three of the amps in the one package to determine "high resistance (maybe open?), low resistance (maybe shorted), and in-range" (just because I could, and because the folks using it wouldn't necessarily be able to interpret simpler signals).

 

It took only a little toying with the input resistance to the amps to not disturb the balance of the bridge... but not much, because a couple-hundred K-ohms input resistance won't swamp the low-ohms resistance of the match's bridge wire.

 

Lloyd

[MadMat]

Hmm I imagine you could also add a few digital gates (or, invert) to feed some indicator LED's for Good, Short, or open.... Hmmm it's got me thinking.....

[lloyd]

Two reds and a green did it without any extra gates!

 

I should add that a Norton, correctly-configured, can act as a gate, too. And one did! <G>

 

Lloyd

Edited January 24, 2016 by lloyd

[MadMat]

It's been a LONG time since I did any electronics work (my test equipment has a big layer of dust on it!), so I had to dust out the cobwebs from my memory. That circuit sounds great! It would need very little current (high impedance) so there would be little worry about accidental ignition from checking the continuity of the ignitors. If designed properly it would be rather accurate as well!

Edited January 24, 2016 by MadMat

[Huggy]

Would anyone be able to show any schematic for this, I was trying to build my own firing system at one point but stopped due to a few reasons but mostly I wasn't able to figure out the test circuit.

[Arthur]

A typical ig will "not fire" at 50ma, but will fire at 500ma. A Typical LED will show enough light at 2ma to indicate continuity or not. Sometimes professional systems cycle through lots of channels at say 1millisec each and produce a display from this.

 

Ultimately if you have lots of cues the continuity check can eat a LOT of power from the batteries and endanger your ability to actually fire the cues.

 

1000 cues at 2mA is two whole amps and this is too much for most dry batteries, and leave the continuity on for an hour and the batteries may not fire the cues.

[lloyd]

"...1000 cues at 2mA is two whole amps and this is too much for most dry batteries, and leave the continuity on for an hour and the batteries may not fire the cues."

-----------------------

Arthur -- just Fooey!

 

If there's a system out there as poorly engineered as to light up 1000 cue lights all at once, it and the purchaser both deserve to "have their batteries die". What a bunch of silliness!

 

In fact, large systems that support a lot of cues almost always test them in groups of 16,32,or 64, with those groups addressable as 'modules'.

 

A maximum of a module's cue lights would be on at a time, and then only in that sort of module where there IS a light per cue. Most large systems use a text or graphical method of examining cue conductivity. And most systems don't apply test current unless you're actually testing! In fact, they don't apply current to more than one cue at a time, doing their tests 'round-robin style' (we called it 'polled' testing, but I have the feeling this conversation is already beyond your actual field experience with real firing systems, Arthur).

 

And last -- Who the hell would rely upon dry cells to fire a fireworks show with 1000 cues? (or forty, for that matter...). Virtually all professional firing systems are equipped with internal gel-cell lead/acid batteries, and almost all of them permit attachment to an external automotive-style battery for backup. If you drain a typical car battery with a 2A load in less than something like 50-100 hours, you have a significant problem with the battery.

 

Lloyd

[mikeg]

Hi,

 

I'm new to the forum and having trouble viewing the attached files, Any ideas what I'm doing wrong ?

 

Schematic.pdf 9.27KB 55 downloads
Silkscreen.pdf 8.05KB 22 downloads
Transfer.pdf 7.7KB 24 downloads

 

EDIT : Now I've made a post it has let me view them !

 

Thanks,

 

Mike

Edited February 20, 2018 by mikeg

[patsroom]

Hi,

 

I'm new to the forum and having trouble viewing the attached files, Any ideas what I'm doing wrong ?

 

Schematic.pdf 9.27KB 55 downloads

Silkscreen.pdf 8.05KB 22 downloads

Transfer.pdf 7.7KB 24 downloads

 

EDIT : Now I've made a post it has let me view them !

 

Thanks,

 

Mike

It may be that you are not opening them but saving them. Make sure you check the correct choice to view them as you have the choice to open or save with each PDF.....Pat

[MrB]

EDIT : Now I've made a post it has let me view them !

 

Thats just how the forum works. You have to have made at least 1 post, to be able to download files from the forum.

[Charles1987]

Hi,

 

I'm new to the forum and having trouble viewing the attached files, Any ideas what I'm doing wrong ?

 

Schematic.pdf 9.27KB 55 downloads Silkscreen.pdf 8.05KB 22 downloads Transfer.pdf 7.7KB 24 downloads

 

EDIT : Now I've made a post it has let me view them !

 

Thanks,

 

Mike

Is there a way to check multiple e-match at one go?

[dave321]

can someone explaine the purpose of the two switches in the above schematic ?

 

are TP 1 + AND TP1- the test pads.

 

where does the top end of r4 connect to,

 

(i'm not very good with some circuits)

Edited February 24, 2020 by dave321