Review: An Inexpensive Wireless Relay

As you know, I’m all for DIY projects.  But sometimes, I’ve got to say, it’s just easier/better/cheaper to buy things.  For instance, let’s say you need the ability to remotely activate/power/E-stop a project you’re working on.  There are literally hundreds of ways you might accomplish this.  The wireless product offerings from SparkFun are quite extensive, and a very simple transmitter/receiver pair can be had for less than a five spot.  But don’t forget, you’ve still got to generate the appropriate signals to the transmitter, and then process those signals at the receiver.  Plus, you’ll want to add a couple of buttons, a relay/MOSFET, perhaps an LED, and of course a case.  By the time all’s said and done, you’ve spent three or four times your initial budget, not to mention all the hours consumed.  Now granted, if you’ve never done something like this before, it’s a great learning experience.  Seriously, if that’s the case, by all means, go for it.  But if your not interested in the experience, why not give this a shot:

Logisys RM01/RM02 Wireless Relay

This is the Logisys RM01/RM02 wireless relay.  It operates from a 12V source, such as a car battery.  The RM01’s relay can handle up to 6 amps and costs just $15.99 at Amazon.  The Logisys RM02 can take 15 amps and sells for $18.99 at Amazon.  I’ve recently purchased the RM01 for a project that has since been cancelled.  However, I’ve still gone ahead and done a little testing.  Here are the key points:

  • In the off state, the RM01 will draw 7.4mA from a source ranging from 8V to 15V (which leads me to believe it’s using a simple linear regulator).
  • When turned on, the RM01 itself will draw between 36 and 64mA as its supply voltage ranges from 8 to 15V respectively (so its coil resistance is about 280Ω).
  • The relay will not fully close until the input voltage exceeds 8.2V.
  • Indoor range (worst-case) with a 12V supply is about 30′ to turn on, 20′ to turn off (I haven’t explored this odd difference, so I’m not sure why it happens).  Outdoor line-of-sight range is about three times that.

I’m pretty pleased with this little guy.  It’s fantastically simple to use, and the two fobs even have red LEDs which light when their buttons are pressed, to let you know that their batteries are still good.

Honestly, I’ve been looking for an excuse to purchase one of these for quite some time.  Ever since a college friend of mine used them to control the power to his self-balancing transporter, they’ve been on my wish list (along with a few other things):

So despite the fact that the project I was going to use them with is no longer proceeding, I’m still happy to have them.  If you have any questions or would like me to do any other testing with the RM01, feel free to leave a comment.

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5 Responses to Review: An Inexpensive Wireless Relay

  1. Jonathan Martinez says:

    I’m using an RM02 in a motorcycle to switch an ignition module and led lighting circuits. Unaware of the 7.4ma draw in the off state, I was puzzled to see that my 12V 7.0ahr power source was drained to 3.14v after 5 or less days. NOT HAPPY! I recharged my power source and discovered the 7.4ma draw. This poses a singnificant problem as the RM02 is the primary “keyless” switch for the system and will see significantly more off status than on status. Is it possible to recycle the draw back to the power source via a capacitor maybe? Please help me!

    • Mike says:

      Hi Jonathan,

      Hmm, so a 7Ah battery drained in only five days? That sounds a little odd to me. Just crunching the numbers quickly, 7 amp-hours is the same as 7000 milliamp-hours, and 7000/7.4 = 946 hours = 39.4 days… Now admittedly, the 7Ah figure is probably pretty optimistic, and only really applies to a brand new battery at a slow discharge, but still I think you’d be good for at least a few weeks. Is the battery fairly old? You might try replacing it.

      Unfortunately I don’t know of any good way of preventing the 7.4mA draw – that’s just a fact of life with this device. There’s no way to recycle the power it consumes (unless you can find a 100% efficient way to recapture all of the heat it produces – and if you can do that, forget the bike, you’ll be a millionaire). You can either disconnect it, get a bigger battery, or just ride more frequently. I suppose one other possibility is to get yourself a little solar panel to keep the battery topped off. Even a half-watt panel would do the trick (it’ll put back 42mA in full sunlight). Maybe something like this.

      Anyway, thanks for the comment and let me know how it turns out.

      -Mike

      • Jonathan Martinez says:

        New battery, but I cant be sure what the amp-hrs were at beginning, obviously it was not fully charged. I was fairly sure that this was just the nature of this type of device. I suppose I could introduce a mini switch (radio shack 275-324) to the system. Because of enclosure constraints, I dont really have room for a relay to handle the constant from the battery to the RM02. Could I place the mini switch on the ground wires of the RM02 without using a relay and worrying about frying the switch? I’m just guessing that opening the ground connection during the off state would stop the 7.4ma draw and render the remotes non responsive until I closed the mini switch. Ideas?

        • Mike says:

          Good point. Yep, you should have no problem putting a small switch in line with the RM02 and ground. That ground connection should only need to handle the 7.4ma of the device (although it will be more than that when you tell it to turn on, but still probably no more than 100ma). The current the device controls to the rest of the system flows through the 12V lines and then back through other ground lines.

  2. fazz says:

    Or just connection to a ignition on circuit such as headlights.

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