Wireless Launch Control

[flight4]

This is my wireless launch controller. Low or high power, it doesn't care. A work in progress over the last few years. I'm calling this one the last prototype. The insides are still incomplete. I'll be capturing the build of this and the wireless field boxes over the next few weeks. Its slightly older brother is a 4 pad variation I built for SoAR for the GRITS regional launch held this month in GA. That 4 pad wireless launched all the M+ projects from the far-away pads at 500'+ with 100% success. The design range is 2000' LOS. Enjoy the build.

[Micromeister]

Very Nice looking layout.

I've been intrested in wireless systems for a long time, but have been reluctant to presue building one as I've always run into the same problem area. Stray signal interference and/or unintended launch by stray signals.

How has your system compensated for these increasing use and channel crowding headaches?
My guess is these are not as many of these problems in less congested sparcer populated regions then here in the East and Northeast??

[Bone Daddy]

I've been designing a wireless controller off and on (mostly off) for a while. Mine uses a touch screen to reduce the number of mechanical switches. Truth be told, I really don't need one. It's just a side project.

It works just like the wireless service at a Starbucks. There may be 10 people on the network, but you only get the information you request. You are automatically assigned a unique ID number (address) that is sent with every request. The computer reads this number, processes you request and sends it back with the same address.

For a wireless launch controller, the trick is that you send a command string from the launch controller to a microcontroller at the pad. The microcontroller decodes the command string verifies it's talking to the right microcontroller and launches the indicated pad(s).

This eliminates the chance of an unintended launch.

The microcontroller at the pad also sends a command string back to the launch controller with a report of which pads have continuity.

I believe most wireless chips have a built in, unique address to prevent the chance of any crosstalk. But even still, without the proper command, nothing would happen.

This is only one approach. I'm interested to hear what Flight4 comes back with.

By the way, to market a wireless launch controller, you would have to have it approved by the FCC and that is a whole different ball of wax...........

Bones

[cwbullet]

Very professional looking.

[flight4]

Thanks for the comments. At first I tried using some very small 433mhz ISM band transceiver modules. These worked well point to point. But developing a protocol for multipoint communications (think multiple wireless field boxes) became more trouble than it was worth. So I switched to 2.4ghz DSSS multipoint zigbee modems. They are awesome. And still only as big as a postage stamp. Better still, they are already FCC certified. I could use the 433mhz modules legally under my ham license if I wanted. But FCC certified is so much better, and the product could be sold if I wanted. The zigbee modems support AES encryption which is critical. With the UHF modules I had to implement my own encryption. On top of encryption I also implement a very strict safety protocol in software to ensure safe launch operations. There are physical safety controls also. This is all transparent to the LCO of course. He just sees a user interface typical of many relay systems. All by design. I'll comment on other features in other posts. Enough for now.

[flight4]

Here's the 4 pad wireless variation (the slightly older brother) that I built for SoAR - Greater Atlanta. The graphics are printed and laminated, vs engraved like the 8 pad version above. But is otherwise virtually identical.

[flight4]

I posted this block diagram a good while back and it hasn't changed too much. It helps set the stage for the build. The system (wired or wireless) is built from modules. Pad modules, relay modules, etc. The same modules are used for wired or wireless, although I've been focused mainly on wireless. A wired system is cheaper to build, however, especially for low power where cable runs are short.

[flight4]

I call this first module the LCO Master Controller. It's only used with wireless since it is the interface between all the pad modules and the wireless network at the LCO end of the system. Despite its central role this module is by far the simplest. Basically a CPU and headers to connect to other things. There's a connector for DC voltage in, power LED, heartbeat LED, sonalert and launch button buss, and a connector for remote programming the CPU. The two header receptacles accept the wireless interface module which will sit over the CPU.

The first photo shows the module with just the SMT components installed. The second & third photos show the mostly complete board. The last photo is the module test fitted into the enclosure. Also shown are the rechargable batteries and voltage regulator. I chose to use two batteries so the system would run as long as possible, say for a three day launch. The 4 pad system just has one battery. The module can measure the input battery voltage so it can actually warn the LCO and eventually shut down if the voltage is getting too low (a safety feature). Of course the system will accept an external battery input also.

The heatsink for the regulator is just a piece of aluminium bar stock. The regulator actually belongs on the PCB, but with a clip on heatsink it actually stands up a little too tall in this enclosure, so it was easier to move it. The module can also accept a backup power supply in the form of two super capacitors. The regulator and the supercaps fill the space to the right of the black capacitor in the second photo. But backup power isn't really needed at the LCO end. So the supercaps aren't installed.

[cwbullet]

Especially is a solder it. It might just short through me. I definitely stick to DC power.

It is good that you only has to replace the one element.

[flight4]

Last thing to do inside the console to finish it up is install the wireless interface daughterboard and the wireless module. This of course is the 'secret sauce' that makes it wireless.

The first photo is the interface module and the wireless module. The wireless module needs to have the right firmware uploaded and a basic configuration put in place. That's done with the little USB interface board. Basically all I have to configure is enable AES encryption, set an encryption key, and set the baud rate to 115k. After the initial configuration the wireless module can actually be configured over-the-air too which is pretty cool.

The last photo shows it all installed. That's it. Even with programming it takes just about 2 minutes.

[cwbullet]

David,

How did you learn all this?

[flight4]

Basically just picked it up over the years. I've always liked to build things.

[flight4]

Time to wrap up the LCO end of the system. The first photo is the completed LCO console still open and all laid out. This is the last we will see of the internals of this box. Except for the ICSP harness, it's not all that bad looking. Someday I'll dig up a picture of the first 8 pad system wired I made. What a nightmare in comparison.

Next the console is all buttoned up. Basically I just set the top in place over the bottom and secured it with a few machine screws. Piece of cake. And also two rear views. Actually I see I have the wrong hardware on the D connector, but I'll fix that later. For a basic charger I just used the one that came with one of the R/C batteries. I simply cut off the Tamiya connector and put on a 2.5mm power plug. Works great.

The antenna is the FCC approved 2.4gHz full wave articulated dipole. Five bucks. With just that type antenna I tested an earlier protoype out past 1500 feet. I was so far away I couldn't even see the pad. The launch was successful (an Alpha III).

Next, on to the field boxes (but not today).