Step 1: What you'll need...
-3 wall outlet sockets (about a buck each)
-1 normal power strip ($10)
- 6 3A 120VAC relays (at DigiKey here $1.8 each)
NOTE: 3A at 120VAC is 360 Watts per socket. If you are interested in remotely controlling a microwave or hair-dryer think about investing a few extra bucks in bigger relays.
- 1 SIS-7C chip from the nice people at Simerec ($19.95)
- 1 IR receiver from Simerec. ($2.99)
- 1 universal remote. I used this one (2$)
- Solid 18AWG hookup wire.
- Any kind of small AWG signal wire.
- 12 ft of insulated wrapping wire.
- Some sort of housing big enough to fit all your stuff. I used a generic Radio Shack one.
- 1 120VAC to DC 5-6 volt converter that outputs at least 400mA.
- if you are adventurous you can build your own power supply! See step 4 for parts and schematic.
My total: $40-50 depending on what you can scrounge.
- Soldering iron and solder
- Protective eye wear!
- Wire cutter/stripper
- Electric tape
Optional but HIGHLY recommended:
- "Third hand" to help with soldering
- Some sort of digital logic board or similar proto-board/breadboard
Please see the last step for additional ideas before starting on your project too!
Step 2: The basic idea
For this project we will be using the Simerec SIS-7C chip which allows up to 7 different logic outputs (of which we will only be using 6) in order to control our relays that will in turn switch on/off power to our sockets. The SIS-7C cannot run on wall current so we will also need to add an internal power supply for the small electronics. The current output from each of the SIS's output pins is sufficient to drive each of our 5V relays so there is no need for any other intermediate switches! YAY less soldering! The SIS-7C also allows a mode for logic switching so there is no need for extra logic flip-flops! YAY again!
Here is a concept design which I sketched out in chalk before starting. It uses output 7 from the SIS-7C to control one socket via a remote. I'm pretty sure the pin-outs are correct but always triple check each connection with the appropriate datasheet before turning on the juice!
Step 3: Programming the SIS-7C
You will definitely need a multimeter or other way of figuring out when the "Program Status" (pin 3) pin goes "high." I had the luxury of using a digital lab with LED logic indicators (shhhh, don't tell the CS department) but the layman will just have to use a DC voltmeter.
1. Setup the IR reciever and SIS-7C on a proto-board.
2. Setup a voltmeter to watch pin 3.
3. Momentarily ground pin 12 (the "Learn" pin) and you should see about 5VDC come up on pin 3 very soon.
4. If this happens, you're golden and you should continue to follow the instructions on the datasheet. If pin 3 does not go high, it's debugging time.
Step 4: Prepping the sockets and little tips from safety Bob...
Safety Bob says...
Wall currents are VERY dangerous. You may die if you ever come in contact with a live socket so always take the greatest care around live wires. Don't touch anything if it's "hot." Always unplug anything before handling it. Another tip I got from my electrician is never touch anything with two hands. If you are electrocuted while touching something with two hands, the current is much more likely to involve one arm, your heart, and your other arm. Getting electrocuted through one finger will hurt, a lot, and you will probably need to go to the hospital... but I know I'd rather take a trip in an ambulance than a hearse.
Step 5: Build/ Test your power supply
If you were lucky enough to find a wall wart power supply lying around, also test that it is working but wait to dismantle it because it might be more convenient to keep it in its plastic housing depending on how small it is.
Below I soldered the two leads of my transformer to each side of the power track. The secondary coil, or leads with lower voltage, are then piped into the rectifier and regulator setup.
Read on if you want to learn a little about how a power supply works:
AC to DC power supplies do 4 incredibly important things in those tiny, ugly, black boxes.
1. They step down your high 120VAC (for US) to a reasonable number, in our case between 6 and 12 ideally.
2. A cooperation of diodes (electrical one way valves) forces this stepped down AC current into a very sloppy DC current so that our small DC electronics can use it! This is also called a rectifier and can be bought as a separate component.
3. Capacitors smooth this bumpy current.
4. A voltage regulator or zener diode trims whatever small, slightly bumpy, DC voltage you now have down to a much smoother and lower voltage current.
Parts list for +5v power supply
- 1 Transformer, 120VAC to 6-12 VDC
- 4 1N4001 Diodes
- 1 470uF Electrolytic Capacitor
- 2 .1uF 100VDC Metal Poly Capacitors
- 1 LM7805 Voltage Regulator
Step 6: Construction
In the final project I used outputs 1-6 of the SIS-7C to control each socket. Make sure that you wire pin 13 or the "Mode Select" pin to ground (conveniently pin 14). This allows each output to act as a toggle so the circuit won't switch off when you release the button on the remote control.
In order for the IR receiver to be "seen" by the remote it obviously has to be visible and not hiding under your desk or table. This is what the insulated wrapping wire is for. Connect about 4 ft of wire to each lead on the IR receiver and twirl it around until it forms a simple signal cord. This was made much easier by hanging a wrench or something heavy on the end of the wires and spinning that around. Make sure to keep track of which wire is which before twirling so you can properly hook it up after your done.
It is handy to program the SIS-7C before soldering it into its final resting place but in case it loses its memory or if I want to reprogram it, I added a couple dead wires to the "Learn" and "Program Status" pins.
Step 7: Testing!
Here is a video of the working (but not quite finished) project in action!
Step 8: Improvements and to-do's
1. Indicator LED's to show whether or not a socket is switched on or off.
2. Indicator LED hooked up to the "Program Status" pin and a pushbutton connecting the "Learn" pin to ground for easier reprogramming.
3. This really should be number one. FUSES!!! My power strip had a built in 15A fuse but PLEASE, PLEASE, PLEASE make sure to add fuses where you deem necessary. Like if your power supply's transformer output is pretty low. Or if you plan on switching anything close to 3A.
4. Cover. I don't have the equipment in my dorm to cut the holes that I wanted in order to properly install most everything, so for right now the components just sit in the project box.
5. Also, I have yet to ground the actual sockets but that should take about 20 minutes. Normal lights don't need to be grounded but it's a good idea to do it anyway in case one of the sockets gets energized from sloppy construction.
6. Because the relays are inductive loads for the SIS-7C it would be a good idea to attach signal diodes to all the outputs. I asked Simerec about this and they said "you should have a diode across inductive loads if driving directly from the chip pin." Another option of course is to use a signal NPN transistor to control the relay.
Please send me your comments and suggestions so I can add to this list!