USB power for Teensy

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enazai

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New to the site, but I checked around for this and I can't seem to get a straight answer. So.
I'm using a teensy 2++ hooked up to an XBee series one radio and a dual relay module (http://www.amazon.com/SunFounder-Sh..._UL160_SR160,160_&refRID=0V3WC9N8BARF25KMGMZ4) to control some AC lights in my house. Seeing as the whole thing is supposed to be hands off once it's installed, I was powering the teensy with a usb cable to a wall charger (5V, 1A). Unfortunately, after about two hours the controller stopped working and I went to check it. Completely fried and too hot to touch. It could be that the relay coils are drawing a lot of current, but I've used these before without any problem, so I'm thinking it's the wall charger. Any ideas on how to power this from the wall without burning out another teensy?
 
looks like the relays use a driver IC that wants
5V 2-Channel Relay interface board, and each one needs 15-20mA Driver Current
Click to expand...

Will probably work on 3.3V.

Need schematic of relay board. and how you wired to Teensy.
Don't let 5V get onto a Teensy GPIO pin setup as an output, even with a resistor in the driver board to limit current to 20mA. That's too high to sink into the Teensy.
 
Always use a transistor and a freewheel diode to drive relays.

relay_driver.jpg
 
stevech said:
looks like the relays use a driver IC that wants


Will probably work on 3.3V.

Need schematic of relay board. and how you wired to Teensy.
Don't let 5V get onto a Teensy GPIO pin setup as an output, even with a resistor in the driver board to limit current to 20mA. That's too high to sink into the Teensy.
Click to expand...

Set up is pretty simple, the 5v and gnd on the relay are connected to the 5v and gnd on the teensy and the two control pins are hooked up to the digital 4 and 5 pins. Xbee is also hooked up to 5v and gnd as well as the software serial pins (digital pins 2 and 3).
 
Unless you are using an adapter for the XBee that has a voltage regulator, you'll want to supply 3.3V power to the XBee...they are not 5V tolerant devices.
 
steve:
plugged a new teensy 2++ into the wall for a few hours, no overheating, so you're right. The issue is definitely the coil current (or transistor current, though that seems unlikely) being pulled by the relay board. If that's the case, is there a way to get around this with an op amp or other and still use wall power or should I switch back to using something that can handle more current, like an arduino uno? Are there other teensy models that can handle the current requirements? My original plan was to use the teensy because it was small enough to fit in the light box, but after installation it looks like I'm going to have to build an external housing anyway so size isn't really an issue anymore.
 
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