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PComp Lab 7: High Current Loads and H-Bridges

This blog has too many pictures of circuits. Here’s Dominique Wilkins in Shanghai with some Chinese fans who didn’t know who he was but knew he must be famous. 我很想中国.

And now, on to the circuits!

DC motors. Fun. I am so not an engineer though. I couldn’t remember in what order the TIP120’s pins are organized off the top of my head, even though we used a passel of them in our midterm. That too I assume will come with time.

I worked with a 3V motor so I’m not sure the current load was high enough to merit the transistor, but I used it anyway, just in case. I ran the motor (which I attached to the gearbox just for fun) with a pot as per the lab instructions, but got bored quickly, so I replaced the pot with a photo sensor and the DC motor with a 1.3V vibrating DC motor. I wasn’t sure how to convert the 3.3V the Arduino outputs into the 1.3V the motor requires using physical components, so I figured that if I pulsed the motor using analogWrite I could approximate 1.3V without damaging the motor. When the light drops below a certain threshold, the Arduino outputs 100 (out of a possible 255) to the motor. Nothing smelled bad or sounded funny, so I’m assuming I figured it out ok. The code is here.

It feels like I’m a step closer to being able to realize my idea of skittish devices that I first explored here.

It took a little doing to get the h-bridge circuit working–I miswired it a couple of times before this:

I kind of zoned out in class while Tom was explaining h-bridges but after putting this circuit together, I understand how they work, which feels pretty good. Two months ago, I was struggling with the idea of a switch. Now, if only I can come up with a final project that works as well as this:


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