Jan 31, 2010

Deconstructing the dSwitch

Dexter Industries was kind enough to send me a dSwitch to try and so I anted to post some of my impressions and tests with it. First, it's seems fairly well built - up to and including tripping over it (OK, I'm a klutz) I had no problems with the casework of connections falling apart... something I'm actually rather concerned with in any device that potentially is carrying household current. Using it could not be easier - you can use a single custom block to toggle the switch "on" or "off" in a very natural way (power users - you can also just use a Motor block in NXT-G to do the same, this is not complex hardware to control).

My first use for this, after just testing it out, was as a Christmas Tree "driver": plugging the tree into the dSwitch with the NXT & sound sensor in control allowed me to make a sophisticated "clapper": one clap to turn on, two claps to turn off, three for a random pattern of flashes, and four claps to "set the trap". When the NXT detected four claps, it shut off the tree and monitored the ambient noise in the room... if it went above 50% of the ambient value, the NXT started flashing the tree. This allowed for a neat "ghost in the Christmas tree" effect. You could set up the tree to surprise the first unsuspecting person to enter the room, which is more than a little surprising. From this it's a short jump to a "surprise" system for folks breaking into a house (open the door and the radio goes on, or light flash... even in distant rooms, with multiple NXTs and BT connections)... or a little sibling detection system (have the NXT not just monitor when somebody entered your room... but have it actively startle them with a light or loud sound. Dave Astolfo's use of an NXT-controlled thermostat system in a aquarium is another good innovative use for this... and I'm sure there's a lot more.

I was also impressed by the speed it could toggle. To be honest, I wasn't expecting much - after all, you don't flick a light switch rapidly most of the time, and relays are often not the fastest things. But in tests, I could shuttle the dSwitch between off and on with an interval of just about 0.01 seconds... roughly 100 Hz (faster than this it "locked up", evidently not completing the opening of the relay before the command to close it again was sent). This allos a lot of nice fast applications for it, especially with rapidly responding lights (like LEDs)... the dancing lights example on the dSwitch page is but one example. You could essentially use ganged LEDs like this as a poor-mans computer-controled strobe light, which certainly could be interesting.

The only real cautions I'd mention here are it's size (it's big, too big for most mobile robots... but if it's mobile, what are the chances it would have something that needs to be plugged into a wall anyway), and the same caution I'd use when plugging anything into a wall socket. When you start messing around with houshold current, you need to be aware of shock hazards, and the same should apply here. But the dSwitch seems well made in this regard too - using UL listed components appropriate for the current and voltage limits, and grounding the system.

I'll be curious to see what folks come up with using "sensors" (actuators?) like this. I'm starting to look at my toaster, or my wife's automatic towel warmer, with a new eye towards DIY ideas... let the user beware!

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