So I am making a wireless rocket launch control system so I can launch my high power rockets with out having to worry about wires. I decided to use xbee radios cause I already have a pair from a different project. I am using a Pro series 1 and am wondering what would be the better way of transmitting the AT through or the API. I need it to be on the faster side so when the launch button is pushed I have less than a second till it closes the relay(s). One way that I thought would help is to send an arm and unarm code as a pad select switch is changed so the other end is primed and just waiting for the launch signal. I would want it to be secured to avoid interference so I plan on using the built in encryption to help with that but also need but I also need it to be reliable with only a max distance of of around 2000 feet. So I do need the distance a little but with the Pro I should be ok. Any advice would be greatly appreciated.
I suggest using the built-in firmware called “virtual wire”. This will take a digital input bit on one Xbee and recreate that as an output bit on another XBee. The two link up via their IEEE 802.15.4 MAC addresses. You could enable the built-in encryption with a shared key to prevent false launches. The delay would be a tiny fraction of a second; imperceptible. This would be for XBee series 2. Not sure if virtual wire is supported for Series 2.
As to 2000 ft… I suggest that the base station end use a 9dBi yagi e.g., from L-Com antennas, and the at-rocket end use a simple short wire antenna. I’ve achived more than 2500 ft. line of sight with such, and with just 10mW on one end. With the XBee Pro’s 60mW, it should be fine.
But you know, on the rocket end, for safety, you might want to use two bits from the XBee, ANDed together. And an ARM switch of course.
Ok, but because of some other features I am including I will be using an arduino at a least one if not both locations. I am leaning toward the API because it has check sum and rx confirmation but I am wondering if this mode reduces distance or speed. If it does is there a way to do check sum and confirmation with at then? I am not sending much data the most I would send at a time is pad number and either 1 or 0 for arming state. I may add a battery indicator on the pad end that will get transmitted back to the control station. At a later time I may add a wind direction and speed sensor but if i have to can make another unit for that.
The API vs. AT command methods are simply two ways to communicate with the XBee. Nothing to do with the radio itself nor its RF characteristics.
The API mode should not be used if you are simply going to use the wireless serial port extension or Digi’s virtual wire.
The API mode gives you a comprehensive API for addressing each frame, etc, for a multi-node system. The API mode is somewhat complex, but if you NEED it, there are several freeware code libraries around.