Long Range Vehicle Detection

[James Sentman]

I still have 10 or so of these things around the house, they are so reliable I forget they are there. They are available in long range 900mhz versions or shorter range 2.4ghz models, and literally dozens of other configurations that making getting the right ones a little intimidating.. The setup is a little arcane but the software has gotten much better since I wrote the original article, it’s much easier to get working now days not least of which because their xtcu software now runs on the Mac so you don’t need to find an old PC to do the setup like I did when I first began working with these things. 

You’ll need 2 of them in whatever configuration you buy, one to connect to the XTension host and the other to do the sensing. Once you have one on the XTension machine they are all mesh networking devices and so you can add more and more sensors or control elements to the network after that. 

You could set one up to wake up every so often and just report it’s presence as Michael said, and setup the pin you connect the sensor output to wake it up and report the pin state change. I looked up the manufacturer of the sensor device I linked to before and the sensor uses 2.5ma when idle and just sensing for changes which is almost nothing. The xBee will spike very short transients when it’s actually transmitting up to 200ma for a few milliseconds, but it’s sleeping current is measured in microamps. You should be able to add both devices to the solar power system on the gate without it even noticing that they are there. You’ll need a 3.3v regulated supply off the battery for the xBee which will also eat an ma or 2 but the sensor itself can run off almost any voltage range that the battery pack might be. Verify it’s within the range first of course, here’s the manufacturer page of the sensor:

https://www.emxinc.com/access-control/product/cs101/

the 900mhz models are here:
https://www.digi.com/products/embedded-systems/rf-modules/sub-1-ghz-modules/xbee-pro-900hp

the much cheaper 2.4ghz models are something like this one:
https://www.digi.com/products/models/xb24cz7sit-004

The 2.4ghz models might actually have plenty of power to reach as far as your gate with the proper antennas. Do have a look through the specs on that to be sure.

if you click on the “how to buy” button it will show you all the different models available of them. Most of the different models are just different antenna connections, I would go with the external antenna connection for a really long range connection but it might not be necessary depending on the actual distance. When looking at the models what you want to make sure is that it’s digimesh or ZB, that it supports the "advanced XBee API “ and that it can be configured with the XTCU program. Don’t buy the ones that are labeled as “programmable” as those won’t work out of the box with XTension. Where the others SHOULD do so. We should be able to use anything that supports that “advanced XBee API” but I’ve only tested a subset of the huge number of combinations of hardware and firmware available for these. They are somewhat expensive in their high power output versions, but they really do work great. They also have many more inputs and outputs available on them that you could use for other things. Most of them have analog inputs, with a simple voltage divider circuit you could use this to monitor the battery voltage in the solar charging system which could be fun. You could also add local motion sensors to the mix and get some alerts if someone or something is hanging out around your gate and such. Probably many more things could be added to it. XTension supports the serial port encapsulation so you could use that to connect pretty much anything with a serial connection to it onto the xBee and pass it through to XTension. If you wanted a W800 out at the gate you could use that to do it… Lots of possibilities.


If you go with an xBee system you’ll also need some boards to hold them on each end and give you pads to solder to for the connections. There are lots of xBee adapter boards. You’ll want one with a USB connection for the XTension side. Make sure to get one that can make enough power to run these higher powered devices. I’ve had trouble with the spark fun adaptor in this way, but the one that Adafruit sells has always worked perfectly for me. For the other side I’d get another adafruit one as they have a goo 3.3v regulator on them already, but make sure your battery voltage isn’t above it’s rating for input voltage.

The XTension wiki page for these radios that talks about configuring them is here: http://machomeautomation.com/doku.php/supported_hardware/xbee

Drop me a line off the list if you have specific questions about them and I’ll do my best

> On Jan 14, 2019, at 10:57 AM, michael <michael at shed.bz> wrote:
> 
> I may be confused, but I think it was said that there is a solar powered gate opener...
> 
> Why can this problem not be solved by an Xbee, powered ON by the physical opening of the gate, by way of a normally open contact switch ?  
> 
> The opening of the gate closes the switch and provides power to the Xbee.
> 
> The Xbee then wakes up and sends the warning signal long before the gate is completely  open.  Also, if the gate opener isn't draining the battery, the Xbee can be powered continuously and come out of sleep periodically to report its existence without worry of battery drain.  ( ignoring extended days with high traffic and no sun ...)
> 
> Xbees are available with a range of much farther than 500 yards.
> I have been using James' Xbee solution for years, and have found it to be very reliable and ever so simple to set up.
> 
> Or am I failing to see the fun of complexifying ?
> 

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