Large Club Control Panel

Looks great so far John

Not sure if this will help or hurt. Attached is the wiring diagram for my 17 pad controller. When I started this project I had no idea where I was going with it, only a very basic idea of how things work. I knew I needed a Satellite system that could handle more then a dozen pads, and wanted an automatic count down option. This thing was designed before affordable digital electronics were the norm...LOL! and this system is also 12/24volt because of the electro-mechanical stepping relay. I have to say it was a Great Leaning experience and great fun as well
If this does nothing but give you an idea of what might be done, I hope it'll show ya don't have to be an electronic guy to design a system.

John,

Here's a schematic for a simple relay launch controller I built a few years ago. It's for a single pad, but it can be easily scaled up to multiple pads. I put a beeper at the pad instead of at the controller. I thought it was more important to hear the "armed" alarm at the pad then at the launch control point. I use a 4-wire telephone cord to connect between the launch controller and the pad.

If the beeper is placed at the launch controller only one wire in needed per pad plus two wires for power and ground. A 4-wire cable could handle 2 pads, and an 8-wire cable could handle 6 pads.

I'll bring my launch controller the next time I make it to a launch.

Dave

Micromeister said:

Looks great so far John

Not sure if this will help or hurt. Attached is the wiring diagram for my 17 pad controller. When I started this project I had no idea where I was going with it, only a very basic idea of how things work. I knew I needed a Satellite system that could handle more then a dozen pads, and wanted an automatic count down option. This thing was designed before affordable digital electronics were the norm...LOL! and this system is also 12/24volt because of the electro-mechanical stepping relay. I have to say it was a Great Leaning experience and great fun as well
If this does nothing but give you an idea of what might be done, I hope it'll show ya don't have to be an electronic guy to design a system.

Click to expand...

Thanks.

For me, the learning experience is a big part of this. My club doesn't need 1/10th of what I have in mind but I want to try it.

DaveHein said:

John,

Here's a schematic for a simple relay launch controller I built a few years ago. It's for a single pad, but it can be easily scaled up to multiple pads. I put a beeper at the pad instead of at the controller. I thought it was more important to hear the "armed" alarm at the pad then at the launch control point. I use a 4-wire telephone cord to connect between the launch controller and the pad.

If the beeper is placed at the launch controller only one wire in needed per pad plus two wires for power and ground. A 4-wire cable could handle 2 pads, and an 8-wire cable could handle 6 pads.

I'll bring my launch controller the next time I make it to a launch.

Dave

Click to expand...

Thanks Dave. Please do bring it. I'd like to see it.

When I get that far along, I want to pick your brain about continuity at the pad. Thats something that is on my list, both at the pad and at the controller.

OK. This is just a baby step forward. I only added a piezo electric buzzer for continuity. I think I have it right here. Wiring continuity is going to get more complex as this develops but lets see if I can get the kindergaden stuff down first.

Since I'm frequently bit by the just build it bug, I recently built a new controller. Nothing fancy. Gets the job done. It was built with parts from my electronics junk box. There is no arm pin/key. It was not built to be used by children. Although with supervision it's kid friendly.

As it is built:

- a common arm switch (momentary)
- led continuity for each launch circuit
- two launch switches (again momentary)
- AA battery built in project box
- 2 standard audio jacks for lines out to pad

Launch procedure:

The use of momentary switches is an important safety feature.

1) Press the arm rocker switch (you must physically keep this switch pressed. If you let go, the system is disarmed)

2) Red led indicates continuity

3) Press appropriate launch switch (launch circuit will only be completed if both switches are pressed concurrently)

4) Release pressure on switches and they automatically return to the disarmed position. (The system can not be accidentally left in the armed position. Hands off, system is disarmed.)

Lines to launch pad is standard lamp cord.
Clips use quick connects so they can be easily changed in the field as needed.

It is imperative that there be an arm/disarm pin at the launch pad. The pin should be removed when anyone is loading a rocket. The launch officer will note there is no continuity while people are at the launch pad. The last person will arm the pad when all is clear.

Next thread for future plans.

I'll go way out on a limb here, without a safety net.

The only real option for a club sized multiple pad launch control system is Handeman's option 3.

A few of option 3 benefits:

1) cost savings
2) ease of setup
3) ease of use
4) safety
5) flexibility

In a nut shell it might look something like this:

A microcontroller based arm/launch device system talks to a microcontroller based launch pad management device via a serial link over a single cheap twisted pair/speaker wire. (Better yet use a radio link. No cables to trip over.)

Arm/launch device tells launch pad management device which pad to activate.
Launch pad management device activates proper relay to launch specified rocket.

Two way communication between the devices handles everything from continuity checks to launch pad status (all clear signaled from pad) to arming proper circuit to etc.

Microcontrollers are cheap, easy to program and robust. I like Atmel chips. Check out www.atmel.com for a look at these amazing things. 8 bit chips are all that's need. There is even enough code examples out there that would require only a little tweaking to make it work as a launch controller.

This is really much easier than I may make it sound. I'll post a more detailed look at this most excellent option in the days to come. This may be the impotence I need to get off my butt and get to work.

Disclaimer: I know, the HoMR sates that remote control should not be used in launch systems. This system would use a robust software based communication protocol. Not a hobby car/airplane remote control.

Here's another couple of questions I'm going to toss out. This assumes that battery means the 12v automotive type.

Would there ever be any advantage to hooling up a pair of batteries in series to boos the voltage to 24v?

Would there ever be an advantage to hooking up a pair of batteries in parallel to supply more amps?

This assumes I remember the terms correctly.

JAL3 said:

Here's another couple of questions I'm going to toss out. This assumes that battery means the 12v automotive type.

Would there ever be any advantage to hooling up a pair of batteries in series to boos the voltage to 24v?

Would there ever be an advantage to hooking up a pair of batteries in parallel to supply more amps?

This assumes I remember the terms correctly.

Click to expand...

Let's look at batteries in parallel first.

Batteries are rated in terms of amp hours or how many amps they can continuously deliver over a 1 hour period. The more amp hours a battery can deliver the more rockets it can launch. So, two identical 12v batteries in parallel can theoretically launch twice as many rockets as one alone can. Why is this so?

Let’s start by running a few thought experiments (Albert Einstein loved thought experiments. Actually he didn’t do any experiments himself, he came up with the mathematical explanations of natural phenomena and challenged others to prove him wrong experimentally) using pitchers of water.

Imagine you have two identical glass pitchers. At the bottom of each pitcher is a small hole with a valve. You fill pitcher A with 8 oz of water and pitcher B with 16 oz. You then open both valves simultaneously. Water flows out of both pitchers at the same rate, but the pitcher A runs dry before pitcher B. Indeed pitcher B takes about twice as long to run dry. Pitcher B has a greater capacity to hold water and can deliver it over a greater period of time if the flow is equal.

In battery speak, this is why a 1.5 volt D battery lasts longer than a 1.5 volt AA battery. It has more capacity.

The average D battery is rated at 12 amp hours (or 12000 milliamp hours)
The average AA battery is rated at 2 amp hours (or 2000 milliamp hours)

Now let’s take two 8 oz pitcher A’s and connect them in parallel so they both flow out of one valve. Pitcher B is again filled with 16oz. Both valves are opened simultaneously. This time they take the same amount of time to empty. The two smaller pitchers in parallel (8 oz + 8 oz) have the same capacity as the one larger pitcher (16 oz).

In battery speak, 6 AA batteries in parallel are equivalent in capacity to 1 D battery.

And why two identical 12 volt batteries in parallel can launch twice as many rockets as a single battery. Together they have more capacity than one alone.

(disclaimer: current draw is a story for another time.)

John:
The very short answer is NO; a single 12volt wet cell or high amp/hr Gel-cell battery is more then needed for LARGE club size launches.
Narhams is one of the larger clubs around, averaging over 100 flights per month at our sport launches sometimes double or triple that depending on the crowd. We use one HD wet cell battery for all launch control power and a second HD large gel-cell to drive the PA. These have Never been even close to drained. On occasion we've run day long launches with a couple hundred flights from a single 26 amp/hr gel-cell on the same equipment as well. I mentioned 24volts on my 17pad satellite system only as it's shown in the diagram, there specifically to run the 24volt coil in a stepping countdown relay that was the only choice I had at the time the panel was built Today it would be straight 12volt.

Bone Daddy said:

I'll go way out on a limb here, without a safety net.

The only real option for a club sized multiple pad launch control system is Handeman's option 3.

...

A microcontroller based arm/launch device system talks to a microcontroller based launch pad management device via a serial link over a single cheap twisted pair/speaker wire. (Better yet use a radio link. No cables to trip over.)

Arm/launch device tells launch pad management device which pad to activate.
Launch pad management device activates proper relay to launch specified rocket.

Two way communication between the devices handles everything from continuity checks to launch pad status (all clear signaled from pad) to arming proper circuit to etc.

...

This is really much easier than I may make it sound. I'll post a more detailed look at this most excellent option in the days to come. This may be the impotence I need to get off my butt and get to work.

Disclaimer: I know, the HoMR sates that remote control should not be used in launch systems. This system would use a robust software based communication protocol. Not a hobby car/airplane remote control.

Click to expand...

BD, I would love to see your design concept for this system. Ground controllers is one of my favorite rocketry subject areas.

I designed and built a 32 pad fully MCU controlled relay system for our club and for NSL 2008 and it worked great. in fact Tripp Barber was the very first LCO to launch from it. Our club continues to use it on almost a montly basis since. With 32 pads in clusters of four we have a lot of flexibility in how we set up our ranges. It's pretty much fool and idiot proof (lol). I'll look in my archive and post a pic of it later.

For the last year or so I have also been working on a new wireless system that is designed to support 64 or more pads, though it's hard to imagine ever needing more than 32. The performance goal is 2000' range over the ground for the wireless even almost all of our launching is from 200' or less.

With the first system I dealt with the issue of safety in a remote control system by keeping the master arm and the launch initiate circuits hardwired to each of the relay boxes, while putting all the other functionality such as pad select, pad enabled, continuity, etc. into the datacomm protocol. This allows us to run just a simple cat5 cable between the controller and the relay boxes.

We lose that hardwired safety advantage with full wireless of course so to compensate I added full AES encryption and CRC checks to the comms. There are also very specific hardware and software related safety protocols that must be met before the remote MCU will allow a launch to take place. All this combines to make an unintended launch a highly unlikely event.

This new system is completed and working on my bench, I just need to get it into some enclosures and do some field testing. Software is about 98% complete. I had posted a block diagram of the system some months back. you can probably find it if you seach my username. I should post some photos.

But back to the OT, yes building a large club controller is a complex project whether you are hardwiring switches to relays or putting it all under remote control. But it's a worthwhile project and the flexibility it enables really gives the club a lot of options when setting up and running a launch. Best wishes and good luck to anyone doing or considering a project like this. And keep posting -- I love to read about this stuff.

flight4 said:

For the last year or so I have also been working on a new wireless system that is designed to support 64 or more pads, though it's hard to imagine ever needing more than 32. The performance goal is 2000' range over the ground for the wireless even almost all of our launching is from 200' or less.

Click to expand...

When we hosted LDRS in 1996 and 2000, we ran 65 pads

Rocketjunkie said:

When we hosted LDRS in 1996 and 2000, we ran 65 pads

Click to expand...

Well there you go. Not so whacko a design parameter after all.

So why does a single 12v car battery launch so many rockets? Here’s more of the long answer, if you’re interested. (See disclaimers) (adapted from rocketry unit lesson plan)

The launch circuit you are designing can be reduced to a battery (B), 2 wire leads with clips, a switch (S) and an igniter (I). It looks something like this:

(+) ------------- S ---------------------}
B I
(-) --------------------------------------}

When the switch is open, it prevents the flow of current (electrons) from the (+) to the (-) terminal, it’s an open circuit. When the switch is closed current flows, but there is very little resistance and the battery sees this as a dead short (short circuit). It is this “very little resistance” that is important to us. It is the dead short that the battery doesn’t like.

Let’s start by looking at igniters. An Estes igniter is a little more complex than it appears.

(see image)

It’s that thin bridge wire that’s important to us. When you throw the switch, there is a rush of electrons trying to get from one terminal to the other. When they hit that bridge wire, there is bottleneck. As the electrons fight their way through the bottleneck, they produce heat causing the bridge wire to glow red hot. The hot wire ignites the pyrogen which ignites the motor. Eventually the fighting electrons produce enough heat that the bridge wire melts. The melted wire acts like an open switch and current flow stops – the electrons can no longer get from one terminal to the next. This takes about 1 second or so with 9 v battery.

(more to follow)

Disclaimer 1: I’m going to use conventional electrical flow where current flows from the positive terminal to the negative. In reality this is backwards. Current actually flows from the negative to the positive terminal. But it really doesn’t matter here does it? If you think it does, then go complain to Benjamin Franklin. It’s his fault anyway right?

Disclaimer 2: igniter image scarfed from the www.

Disclaimer 3: Electrons are fabulous things. The scenario above is only for discussion purposes. PM me if you want to know what those wily little electrons are actually doing.

Bone Daddy said:

So why does a single 12v car battery launch so many rockets? Here’s more of the long answer, if you’re interested. (See disclaimers) (adapted from rocketry unit lesson plan)

The launch circuit you are designing can be reduced to a battery (B), 2 wire leads with clips, a switch (S) and an igniter (I). It looks something like this:

(+) ------------- S ---------------------}
B I
(-) --------------------------------------}

When the switch is open, it prevents the flow of current (electrons) from the (+) to the (-) terminal, it’s an open circuit. When the switch is closed current flows, but there is very little resistance and the battery sees this as a dead short (short circuit). It is this “very little resistance” that is important to us. It is the dead short that the battery doesn’t like.

Let’s start by looking at igniters. An Estes igniter is a little more complex than it appears.

(see image)

It’s that thin bridge wire that’s important to us. When you throw the switch, there is a rush of electrons trying to get from one terminal to the other. When they hit that bridge wire, there is bottleneck. As the electrons fight their way through the bottleneck, they produce heat causing the bridge wire to glow red hot. The hot wire ignites the pyrogen which ignites the motor. Eventually the fighting electrons produce enough heat that the bridge wire melts. The melted wire acts like an open switch and current flow stops – the electrons can no longer get from one terminal to the next. This takes about 1 second or so with 9 v battery.

(more to follow)

Disclaimer 1: I’m going to use conventional electrical flow where current flows from the positive terminal to the negative. In reality this is backwards. Current actually flows from the negative to the positive terminal. But it really doesn’t matter here does it? If you think it does, then go complain to Benjamin Franklin. It’s his fault anyway right?

Disclaimer 2: igniter image scarfed from the www.

Disclaimer 3: Electrons are fabulous things. The scenario above is only for discussion purposes. PM me if you want to know what those wily little electrons are actually doing.

Click to expand...

I appreciate the physics refresher. I understand what you say like I understood it as an undergrad. I just don't have a feel for it. NOTHING is intuitive and when I think a circuit makes sense, I find I've accidently burned down a major city,

When you get around to it, I would be interested on your take on a series connection of batteries. As I recall, that would give me a 24v system instead of 12v, like lining up the D cells for a bigger flashlight. I wa just curious as to whether that might ever have any type of advantage.

A picture is worth a thousand words so here are a few.

This circuit supplies only 5 volts. The offshoot of this is that bridge wire continues to glow rather than melt. This is not good for my power supply so I turned it off.

I tried a few other things:

A single AA (1.5 v) will not set off the igniter.

2 AA in series (3.0 v) will set it off.

Pic 1: Igniter on my breadboard.

Pic 2: Switch is flipped, pyrogen burns. The heat (energy) from this reaction ignites the motor.

Pic 3: Pyrogen is all gone, but bridge wire continues to burn, drawing still drawing 4 amps or so.

(Looks like one of those resistive heaters doesn't it? Or the filament of a light bulb? Not a coincidence)

Pic 4: Bridge wire intact. 9 v and up this is melted. It does show though that it is not the pyrogen that melts the igniter.

Since nobody commented on my previous schematic, I am going to assume that it posed no major problems and go ahead with the next step...or several steps.

1. I added another launch button in parallel with the other one. This may seem silly but there is a reason for it. I plan on a panel mounted push button but we currently use a pistol grip button made from a remote ignition starter. I can see places where having the option to do either might come in handy. Also, if the concept is sound, my supposition is that another ignition switch, (ekectronic countdown) could be added in the same way in the future.

2. I added a voltmeter to measure the potential at the head of the circuit, coming out of the battery. The main reason is that I wanted one but I reason that in trouble shooting, it might be nice to know if I am really starting out with the voltage I think I am.

3. I added a pilot lamp in parallel with the voltmeter. When lit, the system is getting power, even if it is not yet being sent to a pad or cluster.

4. I replaced the micro clips and igniter with a jack icon I drew up.

5. A switch has been added to turn on the pad. right now it seems silly since there is only one pad to turn on but I looking at concept here before I draw more.

6. An led has been added for continuity in parallel with the switch mentioned above.

Do I have it right so far so that I can expand to the next level.

My confidence level up to this point has been relatively good and I feel on safe ground even though I would not be surprised to hear otherwise. Its the next level where things get dicier in my experience. ie unintended consequences.

It matters little but it really only takes a few tens of milliseconds to heat and melt the bridge wire, igniting the pyrogen. Of course this is just the beginning and the ignitor will usually burn for about a second and light the motor.

The only point is the high current flow is usually very brief. Unless of course your ignitor clips touch as they fall away from the motor which happens a lot. Then you have a short circuit. A heavy fisted LCO can actually drain a battery pretty well that way. Not to mention spot welding the clips. Also shorted clips get real hot and can cause a rocket to catch fire on the pad. Usually the ones with the plastic rear ends. Always exciting. This is less an issue when using a 9v battery, or two AAs. More so with a 12v relay system capable of 30A or more into the circuit.

That's one reason I designed voltage and current flow measurement into my new system. I haven't written this particular software routine yet but the plan is to monitor voltage and current real time, and if it appears the rocket should be going or gone and the clips are probably shorted, or were shorted to begin with, open the relay and break the current flow. Maybe at around 500ms. This way the LCO can lean on the launch button until the cows come home and no harm done. Fun stuff.

JAL3 said:

I appreciate the physics refresher. I understand what you say like I understood it as an undergrad. I just don't have a feel for it. NOTHING is intuitive and when I think a circuit makes sense, I find I've accidently burned down a major city,

When you get around to it, I would be interested on your take on a series connection of batteries. As I recall, that would give me a 24v system instead of 12v, like lining up the D cells for a bigger flashlight. I wa just curious as to whether that might ever have any type of advantage.

Click to expand...

Voltage is like pressure. More pressure, more work gets done quicker to light that ignitor. But be careful. Batteries also have internal resistance, so some loads will cause that apparent voltage to drop dramatically. Which is why we usually can't use simple launchers for clusters. The batteries just aren't up to it.

Truth be told, a 12v SLA or lawn mower battery is all that is needed even for clusters. Better to have the battery close to the pad, so the current doesn't have to travel through a lot of wires. That also causes you to drop voltage which is like losing the pressure you want. I learned some lessons early on about that voltage drop. Not for the ignitor but for pulling the launch relay.

flight4 said:

It matters little but it really only takes a few tens of milliseconds to heat and melt the bridge wire, igniting the pyrogen. Of course this is just the beginning and the ignitor will usually burn for about a second and light the motor.

The only point is the high current flow is usually very brief. Unless of course your ignitor clips touch as they fall away from the motor which happens a lot. Then you have a short circuit. A heavy fisted LCO can actually drain a battery pretty well that way. Not to mention spot welding the clips. Also shorted clips get real hot and can cause a rocket to catch fire on the pad. Usually the ones with the plastic rear ends. Always exciting. This is less an issue when using a 9v battery, or two AAs. More so with a 12v relay system capable of 30A or more into the circuit.

That's one reason I designed voltage and current flow measurement into my new system. I haven't written this particular software routine yet but the plan is to monitor voltage and current real time, and if it appears the rocket should be going or gone and the clips are probably shorted, or were shorted to begin with, open the relay and break the current flow. Maybe at around 500ms. This way the LCO can lean on the launch button until the cows come home and no harm done. Fun stuff.

Click to expand...

I am interested in the control system such as you describe and it makes conceptual sense to me. Its just so far above my skill set right now, though, that the idea of me doing something like that is laughable and hard on the insurance rates.

Programing for me is jsut a few steps above basic electricity. I could write a fair Turbo Pascal program back in engineering school (fair, not great) but I never made the jump to windows. Getting down and dirty with the chips was never even an issue.

JAL3 said:

Since nobody commented on my previous schematic, I am going to assume that it posed no major problems and go ahead with the next step...or several steps.

1. I added another launch button in parallel with the other one. This may seem silly but there is a reason for it. I plan on a panel mounted push button but we currently use a pistol grip button made from a remote ignition starter. I can see places where having the option to do either might come in handy. Also, if the concept is sound, my supposition is that another ignition switch, (ekectronic countdown) could be added in the same way in the future.

2. I added a voltmeter to measure the potential at the head of the circuit, coming out of the battery. The main reason is that I wanted one but I reason that in trouble shooting, it might be nice to know if I am really starting out with the voltage I think I am.

3. I added a pilot lamp in parallel with the voltmeter. When lit, the system is getting power, even if it is not yet being sent to a pad or cluster.

4. I replaced the micro clips and igniter with a jack icon I drew up.

5. A switch has been added to turn on the pad. right now it seems silly since there is only one pad to turn on but I looking at concept here before I draw more.

6. An led has been added for continuity in parallel with the switch mentioned above.

Do I have it right so far so that I can expand to the next level.

My confidence level up to this point has been relatively good and I feel on safe ground even though I would not be surprised to hear otherwise. Its the next level where things get dicier in my experience. ie unintended consequences.

Click to expand...

Ok. I'll throw out a few comments for consideration.

I guess I am ok with the voltmeter and lamp1, but not the piezo. The LED inline with the ignitor is ok, you can limit that current by design, but the piezo might draw 50 to 100 milliamps or more and you might light or cook off some low current ignitors like the new Quest ones, or eMatches based ignitors that your members might use. If the purpose of the piezo is to provide audible warning that the panel is armed, then you can just connect it parallel to the lamp1 and voltmeter and that will be good. The pad LEDs will continue to give you pad status.

Now you also want to limit current flow through the LED for the same reason. LEDs can work well with between 8 and 20 milliamps depending on the type, but you'll want to keep that as low as you can and still see it. So a series resistor inline with the LED is a good idea (actually you really do need a resistor). The value will depend on the LED and possibly the length/guage of the other wiring. That can be calculated or even simple trial and error will work (tip: test outdoors in the sunlight).

That said, if you really do need to drive a higher current LED (for visibility in bright sunlight, for example), then you might need to consider adding a simple transistor or darlington transistor type circuit to minimize current through the ignitor. Not too tough but it will add complexity.

JAL3 said:

I am interested in the control system such as you describe and it makes conceptual sense to me. Its just so far above my skill set right now, though, that the idea of me doing something like that is laughable and hard on the insurance rates.

Programing for me is jsut a few steps above basic electricity. I could write a fair Turbo Pascal program back in engineering school (fair, not great) but I never made the jump to windows. Getting down and dirty with the chips was never even an issue.

Click to expand...

Not to worry. There are ground control designs for every skill level. And they all work. That's what makes this such a fun topic. Just like rockets, right?

OK,John... here's where you might be getting into a bit of trouble/undesired consequences:

JAL3 said:

1. I added another launch button in parallel with the other one. This may seem silly but there is a reason for it. I plan on a panel mounted push button but we currently use a pistol grip button made from a remote ignition starter. I can see places where having the option to do either might come in handy.

Click to expand...

Not a bad idea, but you probably want to wire it so that when the user plugs in the remote switch, it cuts out the possibility of the panel-mounted switch from firing - that way there's only one finger that can cause a launch, and everyone should know who it is... its called positive control.

JAL3 said:

2. I added a voltmeter to measure the potential at the head of the circuit, coming out of the battery.

Click to expand...

Good idea to be able to read the battery voltage. You might also want to add an current indicator like an micro-amp meter there, as well, to aid in trouble-shooting.

JAL3 said:

3. I added a pilot lamp in parallel with the voltmeter. When lit, the system is getting power, even if it is not yet being sent to a pad or cluster.

Click to expand...

Unintended consequence of this is that the lamp will continually draw power from the battery. That may, or may not, be a problem. You can minimize the current draw by substituting a voltage limiting resistor/LED in series in place of the lamp. Remember the discussions about the new Quest Q2G2 igniters that would pop when put into a circuit that had a little lamp used as the continuity indicator? The lamp allowed a lot more current to be drawn than the LED/resistor combo: the Q2D2's wouldn't fire with a resistor/LED combo as the continuity indicator.

JAL3 said:

6. An led has been added for continuity in parallel with the switch mentioned above.

Click to expand...

Remember that an LED is just a diode that iluminates. Without some way of limiting the current through the diode, it'll conduct everything you throw at it until it burns up. Thus, a current limiting resistor must be placed in series with the LED so that only a small amount of current (20 ma or less IIRC) is needed to light an LED to it's normal max brightness.

I've just read through the thread for the first time, tonight - a lot of good information there! Thanks for starting, and continuing to feed, the thead!

Wayne

Wayne, Great comment on the interrupt for the remote switch. Here's a twist on that.

At our club launches we sometimes invite our young rocketeers to come up and be LCO for a rack or two. Very closely supervised of course. They get to talk on the PA and all that and they a huge kick out of it. We have been talking about adding a remote switch to our large club controller such that the real LCO retains ultimate control. Basically it is a deadman switch. Plug it in and the launch button is interrupted by the deadman switch. Then unless the real LCO is actually pressing the remote switch the launch will not occur.

Electrically the remote switch is now in series with the launch button vs parallel with it. Pull it out and all is back to normal.

Still all talk at this point but it's a cool idea I think.

Put a 1K resistor in series with the LED. That will give about 10mA as a test current through the igniter. 10mA is safe for all igniters except the old-school flashbulb method. Why a 1K resistor? An LED will have about 2V across it when lit. The remaining voltage needs to be across the resistor. So, R = (12-2)/10mA = 10/10mA = 1K ohms.

As was mentioned, the piezo buzzer might have the same problem. There are all types of piezos, from basic elements to units integrated with an oscillator and driver circuit. Test one of the 12V piezos with an ammeter in series from a 12V battery to make sure the current is <20mA. If not, use a series resistor. Calculate the value of that resistor based on the equivalent resistance of the piezo buzzer. Rb = 12/Ib (where Ib is the current draw with no series resistor). Rs = 12V/20ma - Rb = 600 - Rb = 600 - 12/Ib. Find the closest standard resistor value and put it in series with the piezo. The side affect will be a quieter buzzer.

flight4 said:

... I designed and built a 32 pad fully MCU controlled relay system for our club and for NSL 2008 and it worked great. ... I'll look in my archive and post a pic of it later. ...

Click to expand...

Found it! I have nekkid pix and internal rats nest pix also if anyone is interested.

LED thoughts:

Radio Shack is a convenient source for common LEDs and resistors (most of them are anyway). They are not a good source.

I like Electronics Goldmine (www.goldmine-elec.com) . They deal in surplus, but always have a great variety. Whatever you do, if you're new to the wonders of LEDs just by a whole bunch of them and have fun playing.

Recommendations:

Use a super bright red led. Easy to see even in bright sunlight. Radio Shack will have these. You want to use a water clear led not a diffuse one. Keep in mind you'll be looking down at the panel.

The ones in my controller pics are from EG part # G16750. https://www.goldmine-elec-products.com/prodinfo.asp?number=G16750 These things will knock your eyes out.

You do need a current limiting resister as mentioned. For a 12 volt system a 1/4 watt 330 - 470 ohm resistor should do the job. Depends on the led. The value is not that critical. The specs used in the manufactures data sheet is for continuous illumination. Low voltage/low current LEDs are designed for small battery applications. Since yours will be on only intermittently and you have plenty of battery power, you can really pump up the juice. It will shorten their expectancy from forever to just about forever.

As I said, buy lots and be prepared to play.

I have only messed around with the Estes type igniters and have had no problems.

Check out my scratch built thread for some led pix.

Flight4 - Post all the pix you have. That is a beautiful beast.

I'll try to find pix of a touch screen controller I was working on. It's nice because it eliminates a lot of the hardware. It had password control, automatic countdown with abort and a bunch of other things.

I was actually designed it for a friend before I got back into the hobby.

Yep, that's bright. I noticed those on the breadboard in your earlier pix. Great price.

How do you mount those to a panel?

My fav source is superbright leds dot com. They have T1.75 ~8000 MCD LEDs in colors for about $.50 each. Drive them with about 18ma and fully visible in bright daylight.

I like the low profile panel lenses for mounting but those are getting harder to source.

flight4 said:

Found it! I have nekkid pix and internal rats nest pix also if anyone is interested.

Click to expand...

Absolutely. Very nice piece of equipment.