I blew my Arduino last night and I need to understand why.
With electronics and the Arduino I’m a beginner at best; I know enough to be dangerous and I proved that last night. I am working on a fish tank automation system and a piece of that will be the Arduino controlling a few 120 V outlets to power water pumps for saltwater changes and water evaporation replacement. Rather than starting from scratch with creating the automated outlet system using relays to control the ‘on/off’ for the outlets I decided to purchase some cheap wireless controlled outlets (http://www.amazon.com/Outlet-Wireless-R … 972&sr=8-1) I got them for 10 buck.
I do NOT want to use the wireless feature since I would have no way of telling if the outlets are on/off. I proceeded to pull it apart(outlet control unit) and I found the four main control wires the toggle buttons use. Basically, in testing I found a connection that produces 18V when power is on and 0V when power is off. I also found a supply wire that will flip the outlet from on/off by passing 4-5v. To it (uses a flip/flop so pass 4V to turn it on then 4v to turn it off).
SO, my thought was I would use a Zener diode and a resister to get the 18V value down to under 5 volts to use as a digital in to identify if the outlet was on/off. Then later I would use the other wire as a digital out to actually turn it on / off.
This is where I blew the arduino. Basically, what I did was the 18V output signal goes to one end of the 3K Ohm resistor. The other end of the resistor goes to the Arduino input pin. The cathode of the 5.1V Zener diode also goes to the Arduino input pin and the anode of the Zener diode goes to ground(of outlet low Power DC). I did NOT connect the grounds from the arduino to the ground of the outlet (low power DC ground). Before I made the connection I validated that I was getting 4.5 now from the 18V line. As soon as I touched the (18V reduced) now 4.5V line to the Arduino input the input blew. I did make the mistake of not having the grounds connected (outlet DC ground to arduino ground).
After that blew, I decided (probably not very smart thing to do…) put the ground of my multimeter tester to the Arduino ground and the positive to the 4.5V (was 18V) outlet line. This actually really ‘blew’ the ardino. One of the 24V compacitors(?) actually exploded.
Note:When I refer to connecting any of these lines to the outlet it is/was connected to the low power DC side and NOT the AC 120V side.
Can someone help me out and explain where I failed. As I was working through this I was very cautious and did a lot of testing of the output volts before I tempted any connection to the arduino.
If I understand what you said, there’s no common ground between the AC device and the Auduino.
This is a thorny SAFETY issue. I advise to NOT fiddle with these AC devices that do not have a power transformer and line-isolation. And if later, in operation, this causes a fire, and the insurance company finds that you have a hacked up gizmo that’s not UL rated, they may try to avoid payment.
So I never switch AC stuff with hombrew things.
Why can’t use simply use X10 devices that respond to X10 commands from
-an X10 timer, or
-a PC with an X10 interface and your software or HomeSeer software for smart scripted event driven on/off
-a microprocessor mated to an X10 power line interface such as the TW523; your code on the micro does the scheme you want
If you must DIY on AC power control- then use an optically isolated relay module (solid state relay, for AC loads), whose input is just the voltage/current needed to drive an LED, such as
If you’re a beginner to electronics, I would very much advise against pulling open a line voltage appliance and fiddling with it. Electrocution is not a particularly pleasant way to die.
That said, I see the reason you don’t want to use the wireless part of your switches is because you can’t tell if it’s on or off (ie, what state you’re toggling). Why not have the wireless switch toggle a normal 5V wall wart supply?
You can then feed that 5V supply either directly into your Arduino (watch out for your grounds here!), or have that 5V supply drive either an IR LED, or radio transmitter or something so you get confirmation of the power state.
That way you don’t need to fool with the line voltage device.
You could also use AC-rated opto-relays that you switch using the Arduino. That way the AC has no contact with the Arduino and it would be the equivalent of pulling the cord in/out manually… but digitally.
NotEnoughTime:
After that blew, I decided (probably not very smart thing to do…) put the ground of my multimeter tester to the Arduino ground and the positive to the 4.5V (was 18V) outlet line. This actually really ‘blew’ the ardino. One of the 24V compacitors(?) actually exploded.
Can someone help me out and explain where I failed. As I was working through this I was very cautious and did a lot of testing of the output volts before I tempted any connection to the arduino.
How sure are you that the 18VDC did not have a large AC component riding with it ?