I think I’m thinking too hard

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I’ve been pondering this current-limiting nonsense all day, and I think I’m overthinking.

The issue is this: If I want to get maximum brightness out of my LEDs, I’m going to want to overdrive them a bit because I can run them at a maximum of33.3% duty cycle (if I have three LEDs lighting up at the same time). LEDs that are rated for 20mA of constant current might be rated for up to 100mA of peak current. Apparently, nobody make a 40+mA constant-current LED driver that runs at 3V. Oh well. Continue reading →

A greener watch

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I’ve been thinking more about energy savings with my watch.

I’m already going to be using some kind of Real Time Clock chip so that it only draws a tiny bit of precious power from my battery when in standby, but what about when I power the thing on?

Well, LEDs aren’t current limiting. This means that unless you do something special, they’ll draw a ton of current (and if you supply them with enough current) blow themselves up or at least severely shorten their lifespan. Because of this, you always need to add a current-limiting resistor to protect them.

Here’s how it works: Continue reading →

A Nation of Frustration

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Okay, so soon after I last posted, I started toying around with my old AVR mkII ISP programmer to see if I could get it to work again. It worked at some point in the past, but I’ve reformatted my laptop since then.

I will spare all the details suffice it to say that I spent about 4 hours trying to get the development environment set up, and for like 8 seconds, everything was swell-ish.

Doing Digital

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So, earlier, I expressed an interest in changing my analog accelerometer to a digital one. I found an excellent candidate, the LIS33DE by ST devices, but it had this weird footprint.

My analog accelerometer claims to have a 4x4mm body LGA-16 footprint:
And the digital one has a 3x3mm body LGA-16 footprint:

The LED that burns twice as bright burns half as long

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I was doing a little napkin-math to see what my power/space constraints would be.

Reading the specs of the CR2032 battery, I found that the maximum rated continuous current is 1mA and the max pulse current is 10mA. Typical full-size LEDs take something like 20mA. But even if the LEDs only took 5mA, that’s too much when you factor in all the other crap on the watch.

I’m not too worried about it at the moment though. I’m assuming I can push the battery a little because I won’t be drawing boatloads of current out of it continuously. I took the back off my binary watch and found that its massively bright bank of LEDs runs off a CR2032 and it might have up to 8 LEDs on at a time.