PowerSwitch Tail II

Want to control a standard wall outlet device with your micro controller, but don't want to mess with the high voltage wiring? This might just be the right device for you!

The PowerSwitch Tail II is designed to allow you to safely control an outlet device without exposing any 120VAC voltages. You can plug in any standard 120VAC 3-prong outlet to be controlled by most any microcontroller. This will work great with Arduino! The PowerSwitch Tail II improves on the original PowerSwitch Tail by allowing you to switch a bigger load (now up to 15A) with a wider range of control signals (3-12VDC). The PowerSwitch Tail II can be setup for normally open or normally closed operation by changing a jumper inside the unit with the default set as open.

  • Connect to Arduino, PIC, Stamp, or other MCU with driver transistor or ULN2803
  • LED indicator shows status of control signal
  • Connect output receptacle to a single powered device or to a power strip to control multiple loads.
  • Switches up to 15A (resistive loads) with a 3-12VDC, 3-30mA control signal.
  • [Instruction sheet](http://cdn.sparkfun.com/datasheets/Components/General/80136 PST II Instructions 2015-11.pdf)

PowerSwitch Tail II Product Help and Resources

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Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • -------------------- Tech Support Tips/Troubleshooting/Common Issues --------------------

    Designed for Wall Outlets

    If this is not working, make sure the PowerSwitch Taill II has the plug plugged into a 120 volt AC outlet. Another support representative indicates that the relay inside won’t work without AC power.


    Even though the data sheet we list doesn’t say so, a customer reports that there is a jumper inside these that let you select NO or NC relay contacts. The datasheet will have more information about the jumper inside the enclosure.

  • Member #633356 / about 7 years ago / 1

    A question...Is it UL listed? I don't see any markings to signify that it is.

  • Member #99987 / about 8 years ago / 1

    Is this either "normally open" or "normally closed"? If NO, then how hard it is to rewire to NC - or can that be easily achieved with the microcontroller?

    • CF / about 8 years ago / 1

      The relay inside is N.O. and that can't be changed. With no input to the device, the relay will be off. Supplying 3-12 volts to the input will close the relay and turn on your load.

      • Member #99987 / about 8 years ago / 1

        Actually there's a jumper inside that can easily be resoldered to NC.

  • VladRoss / about 8 years ago / 1

    Need 240 VAC version for Europe.

  • 172pilot / about 8 years ago / 1

    Looking at the instructions / schematic, the "ground" pin is just hooked to the 3rd prong AC ground.. I should be able to ignore that pin then, right? All the low voltage DC side electronics are completely isolated from this anyway, and so this looks pointless to me..?? Am I missing something?

    Shouldn't I just be able to hook up ground and a digital pin from an arduino and work this thing just fine?

  • Audiobuzz / about 13 years ago / 8

    A 240v version with IEC plugs would be ideal for us non-us folk.

  • Finally, a Sparkfun product that doesn't try to kill you.
    It sure beats the old relay on the bench with test clips trick. It only works with 120 VAC, but it's controllable with a single I/O port at 3V to 5V. I'd leave the ground terminal unconnected to avoid a possible ground loop; it's fully isolated anyway.
    Plus it costs less here than from the OEM. Gotta have it!

  • Member #62923 / about 13 years ago * / 3

    This is a very cool product. But if you are just looking for an easy way to avoid being exposed to high voltage, an alternative is to modify one of those remote controlled switches. They are wireless and come with a remote and one or several power sockets. You can get them in many retail or online stores for cheap. All you need to do is to modify the remote -- use a MCU to simulate a button press, (often as simple as sinking one button pin to ground). I've tried this before and it works quite well. And it's even wireless!

    (Update) check this page: <a href="http://rayshobby.net/blog/?p=936">http://rayshobby.net/blog/?p=936</a> for example.

    • bbotany / about 12 years ago / 1

      Watch out for RFI. During thunderstorms I get to watch a lot of on-off switching with my wireless outlets.

  • So... Why not just buy a relay?
    Two of these: http://www.sparkfun.com/products/10636 in parallel would be rated at one amp higher, and all for less than half the price of this.

    • Sciguy / about 13 years ago / 9

      The whole point of these is so you never have to deal with exposed high voltages.
      The relay, you'd have to wire them manually to 120volt sources.
      A lot of people (like me) aren't really comfortable with that.
      This is just plug in the appliance, and plug in a low voltage controller circuit, whether its an arduino, or whatever.

      • 120 volts is no problem. You just have to go with the one hand rule, and know what you are doing. The worst thing that could happen is the circuit breaker getting blown, and maybe part of your project is a little darker than it was. ;)

        • M-Short / about 11 years ago / 3

          That's the problem "know what you are doing" a lot of people don't. I've used these and you can't make it easier for people to not electrocute themselves with mains power.

        • hithere / about 13 years ago * / 2

          I don't understand why one would have to work with hot 120VAC wires when making a device using relays? Why not pre-wire everything in an enclosure with proper AC wires/plugs and plug into the wall socket only when the project is 100% ready and there's no 120VAC circuitry exposed? I think it's so easy to do.
          But this product is clearly for those who doesn't want to or can't create smth like that.

          • boj / about 12 years ago / 5

            Some people are afraid to have any vulnerabilities to error so they use these. If you wired something wrong in that box, there is a chance that it could short out your power.

  • boj / about 12 years ago * / 2

    If anyone wants some Arduino example code, see the following. This makes it so when you press a button it goes on for as long as you press it.

    Button is connected to Ground and 2. Relay is connected to 13, 5 volts, and Gnd.


    const int relayPin = 13;  //change these to change pin numbers
    const int buttonPin = 2;
    void setup() {
    pinMode(relayPin, OUTPUT);  //initializes the pins defined above
    pinMode(buttonPin, INPUT);
    void loop() {
    if (buttonPin == LOW) {    //if the button is grounded
    digitalWrite(relayPin, HIGH);     //turn the relay on
    else {
    digitalWrite(relayPin, LOW);  //if the button is not grounded, turn the relay off

    Edited to clarify.

  • These sell out to quick but I found a good video on how to make one of these. DIYPowerTail

  • Member #585169 / about 10 years ago / 1

    Bought this problem and have a problem getting it to work. I supply a drive from a signal generator (2 s pulse), the LED lights up but the connected device doesn't get powered. When measuring the output voltage, without a drive signal, the voltage reads 122V, with no load attached this goes down to 115V (line Voltage) when drive signal is applied. No sound audible from the relay switching.

    Any idea what might be wrong besides that the device is faulty?

  • ctdahle / about 11 years ago / 1

    I keep putting moving this back and forth between my wishlist and shopping cart because they always seem to be out of stock when the rest of my order is ready. Just wondering, is it because they are really popular, or is supply really scarce, or what? Seems like they would not be that hard to make and it surprises me that someone hasn't come up with a competitive product with a bit more constant supply.

  • wenjiun / about 11 years ago / 1

    I try to control the on off of a LED light bulb, in the on position the bulb light up very bright but in the off position the bulb still has a extremely dim light (not totally off), is it normal?

  • Member #373318 / about 11 years ago / 1

    When will this be back in stock?

  • Maxwellfire / about 11 years ago / 1

    A while back, I found a device that looked like a octopus, with each of its arms being an outlet that was controllable by a build in relay. Does anyone know what product i'm talking about? Any help would be greatly appreciated. Thanks

    • The Doctor Doge / about 11 years ago * / 1

      I have seen one of those, but the seller didn't seem too keen on manufacturing any. liquidware.com relay squid

      • Maxwellfire / about 11 years ago * / 1

        Thanks. I swear it was being sold by sparkfun though. And if my memory holds, It was white.

        On second thought, that looks right, as I bought something from liquid ware and must have seen it there

  • boj / about 12 years ago * / 1

    Do you sell just the PCB? I wanted to make an Arduino clone on a perfboard and solder wires to this.

    Edit: Never mind. Found a Sparkfun schematic for a relay control thingy and I soldered it up on a stripboard and it works! Find the schematic that I used here, just scroll down to the schematic.

  • mattproc / about 12 years ago / 1

    Did this go up in price or am I misremembering?

  • Member #226770 / about 12 years ago / 1

    A demo code example for mbed with photos and a video is available at http://mbed.org/users/4180_1/notebook/powerswitch-tail-ii/

  • NTICompass / about 13 years ago / 1

    Woohoo back in stock. Let's see how long these last.

  • Ravenkallen / about 13 years ago / 1

    Dang!! Out of stock already? Any idea when you guys will get more?

  • swort / about 13 years ago / 1

    Where there be one with european plugs (2 round pins) ?

  • Nardella / about 13 years ago / 1

    How fast can this be cycled? Enough to do fading/pwm?

    • ctdahle / about 11 years ago / 1

      Also, only rated for 100,000 cycles. You could run the lights and heaters in your internet connected chicken coop for years, but you'd wear it out in a few minutes if you tried to use it for PWM.

    • mjkuwp / about 13 years ago / 1

      I wouldn't think so. The linked data sheet states this:
      Operate times: 15 ms max actuate, 10 ms max release

  • Majik Sheff / about 13 years ago / 1

    Wow, I've been building these things for years now at work to switch equipment on and off in unison with other equipment.
    I had a crappy cable modem a while back that would randomly lock up, so I set up a cron job on my firewall box to ping a server periodically.
    If it didn't get a response, it would pulse one of the parallel port's polling lines that was connected to a relay in line with the cable modem's power.
    It's nice to know I can get them ready-made now. That will make my boss happy.

    • Nelson.r.o / about 13 years ago / 3

      Had a similar setup on my router except that I also made the control program log the date/time of the downtime it helped me get out of a contract with a ISP, the routers they issued to costumers would just lock at peak hours and had to be power cycled to try to get a new connection.

    • hithere / about 13 years ago / 1

      Which relay control schematic did you use? Can you provide a link, if there's one you know? Thanks

  • CrazyP / about 13 years ago / 1

    What's the max inductive load? I'm thinking about controlling a small air conditioner (or maybe refrigerator) with one of these.

    • MikeGrusin / about 12 years ago / 1

      These are true relay contacts, not a solid-state device, so your maximum inductive (start-up) load in Amps should be below the relay specs (15A).

    • Member #3698 / about 12 years ago / 1

      I too would like to know the max inductive load for cooling uses.

    • Yea, you guys should list the maximum VA rating as well... They are not the same!!

Customer Reviews

4.3 out of 5

Based on 7 ratings:

Currently viewing all customer reviews.

2 of 2 found this helpful:

Does what I need it to

Was looking to tinker with some control lights in my office with an Arduino, and didn't want exposed wiring or the hassle of the containment of it. This may be a little pricey up front, but will definitely be ordering more in the near future. Pro tip that helped me out: Use a set of old Cat 5e wire and split the wires to get a nice cord you can use for this and run a distance if needed.

works well

I use it to turn on the amps and speakers when my projector is on. Saves me from having to go switch them on each time i want to watch something.

works fine

Works fine

Just what I needed!

Had a huge project for school and needed a couple of these to program to power some key components. Best programming purchase I've made thus far.

Just what I wanted

I wanted to use my Arduino Uno to control the temperature in different molds that I have for creating carbon fiber parts. I know that with a few hours work, and a few dollars, I should be a able to make a relay based system for switching the heater (in this case a 250 Watt bulb). But, for the modest extra cost of the Power Switch Tail, I saved my self at least an afternoon and possibly an injury. It does what is says, appears robust, and I am happy that I purchased it.

Easy to use for an IoT class!

This was very easy to use and will make doing an IoT primer class pretty trivial.

Anyone know how to hack these things so I can get the power to run a Sparkfun Thing Dev from the Tail itself rather than needing an additional power outlet to power the Thing?

There's really not a good way to hack this to split out a pre-relay DC converter. But since it is really just a relay in a fancy housing, you could create one on your own with something like our beefcake relay.

Works, but sort of expensive

I would recommend the Beefcake Relay instead.