What's my best tech choice for low power, mid range remote switch?

Discussion in 'Wireless & RF Design' started by s_mack, Jul 20, 2016.

  1. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    I have little experience with wireless design.

    I want to remote launch a weather balloon when conditions are right. I considered programming in all the data from the various sensors and just have it auto-launch... but the expense of the equipment on the balloon has me thinking I would rather get the data and then manually send the command to release, just in case I have a bug in the code (ie. it will alert me when it thinks it should launch, and I give it the OK).

    The problem is where it is stationed. It isn't particularly far away, but it is difficult terrain and the weather conditions I'm trying to capture don't make a hike out to it a welcoming proposition. So wireless is the way to go. But what flavor?

    It is way too far to pick up my house's wifi (I lost that just going about 30 feet from the building).

    Should I extend wifi with an outdoor directional WAP?
    Zigbee?
    Cellular?
    Would an off-the-shelf r/c setup work at that distance with a patch antenna on my end?

    Cellular seems overkill because I have line of sight and we're only talking about 1.5km, but then 1.5km might be pushing it for other methods?

    My two primary considerations are cost and power consumption. On the remote end, it would have to be run by battery and I would want it to operate on the order of months, if not years. I certainly don't want to go up there every 2 days to swap batteries.

    Thanks.
     
  2. BR-549

    Well-Known Member

    Sep 22, 2013
    1,981
    388
    If it isn't far away, how bout a pull string or fishing line and a slip knot?
     
  3. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    I'm not sure if that was a serious answer :)

    1.5Km = pretty much a mile. I'm thinking that's too far to tug on a string, no?
     
  4. BR-549

    Well-Known Member

    Sep 22, 2013
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    Pardon me s_mack, I misread your post. Too much medication.

    What equipment do you have at the launch site now?
     
  5. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    Well, a bunch of complicated "stuff"... that there's no reason to really get into. Attached to "stuff" is a relay for turning it on. Attached to that is an Arduino for "flipping the switch". I want to wirelessly communicate with said Arduino. I have a wifi shield for it, but as I said... it is way out of range for that with the equipment I currently employ (I could try a directional antenna on my end if there's hope that would work?). I have a cellular module on the way, but it is much more complex to hook up and drains the battery more (I think) and also costs money for the SIM card and cellular plan - which is OK if it is the best method to choose. I'm just not sure if it is or not. I don't have anything Zigbee related - nor any experience with same - but if that's the way to go, I'll go that way.

    I can go just about any route. I was just hoping for a shortcut if someone's been down this road before and knows which way is best for this scenario.

    Right now, the Arduino uses only a few dozen uA in standby and it only needs to come out of standby for a few seconds a few times per day to send me the sensor data and look for a return command (I don't need to launch in realtime - several hours delays is fine). So as it is, I think I can stretch a battery for years. But that's with no wireless involved. Therefore, I have to be power conscious with whatever wireless system is employed.

    FYI, in case you're wondering - the "stuff" has its own solar power/battery, but I'm not authorized to monkey around with it to borrow power from there, presuming there's enough to borrow. So the switch part has to be self sufficient, power wise. I could hook up a 2nd solar system to the Arduino, but was hoping that wasn't necessary. I guess it is no big deal if it is.
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
    1,981
    388
    OH......yes...try a directional ant on both ends of your wifi first. It can be illegal to put a directional ant on some wifi units. But it will indicate the power needed.

    I assume you have a cabinet. You will want a solar panel and a controller for it.

    There are many LOS data radio options available. Almost all are just radio modems with rs 232 or rs 485.
    It's been a while since I put one in, but with today's stuff, I'm sure you can find data radios that use uprocessor communication protocols.

    You will need to consider LOS (line of site), terrain, local rf regulations, frequencies available, power allowed or needed, whether an omni or directional ant is needed. And other transmitters in the area. A radio survey.

    I put in hundreds of LOS (wireless) weather stations in years passed. If you can program the arduino, you should be ok. There are many off the shelf boards you can use. You may poll the station at any time, and the station can also send out alarms.
    All my work was with 450. Which would easily handle your problem. But this new ghz stuff is most impressive. The speced range and power is hard to believe. And a smaller antenna.

    I certainly wouldn't go with cell.
     
  7. jsallas

    New Member

    May 17, 2016
    9
    1
    Hey s_mack

    Any ZigBee module will be enough to cover that distance with a cheap antenna (I have tried with XBee and whip antenna).
    The less Data rate you use is better, since you will minimize your package loss on that distance.
    This won't drain your battery as fast as WiFi and you can get some decent sleep mode currents.

    A second choice could be an off-the-shelf r/c module. Sub-GHz frequencies would do a better job because of the wave lenght.
     
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