Netduino home hardware projects downloads community

Jump to content


The Netduino forums have been replaced by new forums at community.wildernesslabs.co. This site has been preserved for archival purposes only and the ability to make new accounts or posts has been turned off.
Photo

Pyrotechnic Sequencer


  • Please log in to reply
8 replies to this topic

#1 Matt Taylor

Matt Taylor

    Member

  • Members
  • PipPip
  • 15 posts

Posted 05 July 2011 - 04:56 PM

Hi All, Here's the first actual thing I'm doing with the Netduino. I'm working on a short film, and we need to do a shot where I get shot in the shoulder. We did a trial run of the pyro side of the effect this afternoon, and now I'm working on the best method of sequencing the real effect. What the scene requires is that I will be running away from the bad guys, when I get shot through the sholder, with a small blood pack on the back, and a larger one on the front as entry/exit, and then maybe another dust/sparks pack on a wall about 6 feet in front of me. The camera will be wide, from the side of me, So I want to sequence the blood/dust packs so it looks like the shot goes in my back, out my front and then hits the wall. Here's the circuit I'm planning to build to trigger the blood/dust packs (called Maroons in the UK). I'll have 3 of these all running off the same safety key, I just drew one cos i'm lazy :D I would appreciated some feedback on the circuit design, and the project as a whole. I'll add a vid of the test as soon as I get it, and put up code/hardware as I design it. Thanks for reading! Matt

Attached Files



#2 Mario Vernari

Mario Vernari

    Advanced Member

  • Members
  • PipPipPip
  • 1768 posts
  • LocationVenezia, Italia

Posted 05 July 2011 - 05:59 PM

That's intriguing!...This forum is somewhat amazing for the several applications! First off, I don't understand WHAT is, or WHO is (or even in WHICH way) the circuit will be actually triggered. Is it a switch within the gun? Secondly, there is another post, similar to the your's, involving hi-speed photography. That guy had to trigger a still-camera a bunch of millisecs after a photocell reveals a bullet, a drop, etc. The problem wasn't the circuit, but the precision of timing with Netduino. Well, the real problem is that Netduino runs "managed" code, which is garbaged, and there is some background work. That means you cannot be sure to delay 1 or 3 ms, for example. The actual delay is unpredictable. There is a third point also about the circuit, that could be a lot simpler. I don't know the characteristics of a "maroon", but I think the R3 is totally useless. Then, you choice to use a mosfet is great, but you may connect the gate of the mosfet directly to the Netduino output, without be scared. I may even point out that your circuit could have a problem: there's no any real way to pull the gate to the ground to inhibit the mosfet. I'd simply avoid the transistor and all the resistors. Just connect the gate to any output. Only an exception. The Netduino output gives +3.3V, that could be not enough for the mosfet. Well, it depends on the mosfet threshold. In this way, you may consider to drive the Netduino output as "open-drain", with a pullup to +5V. Hope it helps. Cheers
Biggest fault of Netduino? It runs by electricity.

#3 Matt Taylor

Matt Taylor

    Member

  • Members
  • PipPip
  • 15 posts

Posted 05 July 2011 - 07:16 PM

Hi Mario, thanks for your feedback!

First off, I don't understand WHAT is, or WHO is (or even in WHICH way) the circuit will be actually triggered. Is it a switch within the gun?

I'm trying to design this as a general timer for pyro. In this instance we will be using a push-button that I will have in the palm of my hand that will go into one of the DIO pins on the board (probably carried in a belt-pouch). This will have an event attached to it in code that will trigger each squib/maroon in succession, with pre-programmed delays.

Posted Image
Here's the set-up we used to test the blood pack with today. It's a push button with a 9V battery. This is a prety common setup for doing single shots in film and theatre, as it can be hidden up the actor's sleeve.

Pushing the button connects the squib/maroon across the battery. A cool thing was using a detachable battery connector, so I could hold my hand over the battery pins while we were setting up to make sure the circuit could never bee made until we were ready to go hot. Safety first :D

In future though, It may be useful to have either something on a gun to trigger it, or even some sort of audio/visual count-down timer that we can use to sync up everything. This would depend entirely on the scene being shot.

The problem wasn't the circuit, but the precision of timing with Netduino.


That's DEFINITELY interesting to know. I'm not sure what delay the squibs/maroons have themselves, and the variability in that.

I'm hoping to be able to experiment with that to determine if this is even the best option.
Last night I talked to a member on the forum chat, who is doing a similar system for launching rockets. He suggested that I should not expect any accuracy under 20ms, due to the variance in the igniter. (please correct me if I have miss-understood this).

The stunt we are planning is to have the entry/exit very close together, maybe 50ms, and then the wall hit around 100ms after that. We're not aiming for massive realism here as far as speed and timing, more to create the illusion that the shot has passed through and hit the wall.


As for the circuit, this is an initial sketch, and I'm interested in any feedback.

but you may connect the gate of the mosfet directly to the Netduino output

The MOSFETs that I am using for this were originally brought for a motor driver that I decided to replace with a single IC, as they were way over-spec for the motor I eventually ended up using.

I tested a few different circuits, and found that the voltage required on the gate is too high to drive them right out of the Netduino DIO pins, which is why i've opted to use the first transistor (just a generic low power NPN type). I was not sure how well the smaller transistor would conduct, So I've opted to use R2 to lower the voltage there a bit. This may not be required.

I'd simply avoid the transistor and all the resistors. Just connect the gate to any output.

In this particular application I wanted to be definitely sure that the base on the first transistor is pulled down to ground, because if that went high for whatever reason (and in experimentation we found that just static from someone touching the breadboard could do that without a pull-down), the charge would go off, which could result in anything between the annoyance of having to re-set everything or a ruined take, up to someone loosing a finger or even worse :P

If it would be a good idea to also pull the gate on the MOSFET down to ground, then I would definitely want to do this too.

I don't know the characteristics of a "maroon", but I think the R3 is totally useless

Agreed there, I don't either :D

R3 is there because currently I don't know the resistance of the squibs (my multimeter is on loan to my brother). I added that in provisionally to limit the current, as I don't want to damage the MOSFET or anything else when the squib is triggered. Triggering should essentially create a short-circuit between the battery and ground for a few fractions of a second.

Once I'm able to measure the resistance through the squib and MOSFET, I'll re-evaluate this part of the circuit.

Thanks for your feedback, I'd rather someone tell me off for failing at electronics now, instead of setting light to my hair or something in front of a camera crew :D

#4 Mario Vernari

Mario Vernari

    Advanced Member

  • Members
  • PipPipPip
  • 1768 posts
  • LocationVenezia, Italia

Posted 06 July 2011 - 04:21 AM

Matt, now the things are much clear! Well, I'd use the schematic as the attached one. Please do not consider the mosfet model: the editor has its own models and I won't change them. Also, the inductor coil stands for the maroon. Since the maroon contains an inductor (i.e. an electro-magnet), I'd add a normal diode. That's for prevent extra-voltages and spikes that could damage the mosfet. So, the mosfet threshold is higher than 3.3V... Well, you circuit is not able to pull the gate voltage over 3.3V. I'd say that the voltage is even lesser, because the base-emitter voltage drop. Moreover, there's not anything pulling the gate low. I'd suggest a more complex circuit, using two kinds of transistors: one is NPN (e.g. 2N2222, BC237, BC337, etc) and the other is PNP (e.g. BC307, BC327, etc). Basically the circuit is an amplifier. The capacitor is useful to prevent unexpected behaviors during the transient. I mean as the safety switch is turned on: obviously the maroon should NOT blow! Finally, it's important to avoid to left floating the gate of the mosfet, as in your schematic. The mosfet works by a charge of electron feed on the gate: no current, only charge. Any electrostatic charge could be enough to polarize the mosfet, so the maroon will blow. About the timings...I guess there's no problem if you need many millisecs of delay. The 20ms reliability is absolutely right. Hope it helps. Cheers PS: looking forward to see the film!

Attached Files


Biggest fault of Netduino? It runs by electricity.

#5 Matt Taylor

Matt Taylor

    Member

  • Members
  • PipPip
  • 15 posts

Posted 06 July 2011 - 06:52 PM

Cool, thanks for your help. I'll simulate it and breadboard it out later this evening and share how it goes. I finally got the raw footage of the single squib test back from the camera guy and uploaded it to youtube. I think that I need to work on the positioning a little bit, and also my own timing, I think I was way too quick on the draw.

#6 Matt Taylor

Matt Taylor

    Member

  • Members
  • PipPip
  • 15 posts

Posted 14 July 2011 - 06:12 AM

Hi All, Apologies that this project has gone quiet, I've been really busy with other work, and only this morning had a few hours to get back to this. I've simulated the circuit you sent over Mario, I'm happy with how it's working. I need to order in some components, and I'll prototype it and test it with a few squibs. I've attached a screenshot of the simulation. What is a good open-source simulator? for little projects, I've always used Yenka (was previously called Crocodile Clips) that I still have a student licence for from school .. 10 years ago. If there's an open source sim that anyone would recommend I check out,that would be great. As you can see, there's only 0.2 micro volts across the squib when the key switch is closed, and 9v when the netduino DIO goes high.

Attached Files



#7 Mario Vernari

Mario Vernari

    Advanced Member

  • Members
  • PipPipPip
  • 1768 posts
  • LocationVenezia, Italia

Posted 14 July 2011 - 06:56 AM

Matt, I didn't comment your trailer: my apologies!
It's simply great!...But is it anything serious? I mean, will we see anything on the big screen/TV?

I am happy that the circuit fit your target.
I know Yenka, but it's too restrictive as licensing, IMHO.
Here are a couple of free simulators, both very powerful (at least for hobbists):

From Texas Instruments here is Tina. In the truth it's a Hungarian company, named DesignSoft. This sim is *very* well done.

From Linear Technology here is LT Spice. Not at the level of Tina, but surely enough even for a circuit designer.

Cheers
Biggest fault of Netduino? It runs by electricity.

#8 Matt Taylor

Matt Taylor

    Member

  • Members
  • PipPip
  • 15 posts

Posted 15 July 2011 - 01:22 PM

Cool, I'll check those out.

We are gradualy putting bits for the film up. All the indoors scenes will be filmed infront of an audience at a local theater, and we will ahve some demponstrations/workshops showing off things like editing and makeup effects.

Here's a rough edit of what we shot last weekend as a trailer,
http://www.youtube.com/watch?v=8s1CoDm9HDg

Unfortunately we did not shoot any pyrotechnics, as we were filming on public land.

You can follow the project on our website.

#9 Stuart Crawshaw

Stuart Crawshaw

    Advanced Member

  • Members
  • PipPipPip
  • 60 posts
  • LocationLeeds, United Kingdom

Posted 15 July 2011 - 04:22 PM

I've always used Yenka (was previously called Crocodile Clips) that I still have a student licence for from school .. 10 years ago. If there's an open source sim that anyone would recommend I check out,that would be great.


Just for info, If you didnt know already, Yenka has a free license for Home users
Intelligent People Aren't Afraid To Ask For Help.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

home    hardware    projects    downloads    community    where to buy    contact Copyright © 2016 Wilderness Labs Inc.  |  Legal   |   CC BY-SA
This webpage is licensed under a Creative Commons Attribution-ShareAlike License.