Over the last few months I’ve been revisiting some foolish assumptions that have cropped up over the course of this project, and squashing them.
1. I am bad at soldering / this soldering iron is a dud
After many awkward, fumbling, frustrating soldering attempts, I was on the verge of buying a fancy new solder station – even other folks were having trouble helping me out or giving me lessons. A curse.
In a last ditch attempt to salvage things, I got some new solder, and suddenly everything flowed right where it belongs, in perfect little dollops. I felt like a damn magician.
The issue seems to be with the lead-free solder I was using. It was so sticky and uncooperative – even at high temperature – that I’ve become an advocate of the old-fashioned, slightly more poisonous way of doing things.
2. I have to assemble endless identical power switching circuits
A couple months ago, I was preparing to put together small switching circuits for all the solenoids I want to power in this project. But my gut (cultivated by programming) gurgled:
Someone already solved this problem, and solved it better.
Enter the H bridge.
An H bridge circuit does everything I need and more: it switches high power circuits via low power control signals, and it will also invert the polarity of the output voltage. That means you can run a motor forward or backward.
This switching capability is only necessary for bi-directional actuators like motors (or latching solenoids – perhaps something to play with later). But for now, I can use the basic switching functionality and ignore the flipside.
An H bridge can also short the circuit to “brake” a motor, which could turn out to be useful in future testing.
Pack this up, add some features like protection against overheating, and you’ve got the integrated circuit I’ve been looking for. It’s more reliable, more efficient, and cheaper than the individual components I’ve been using.
One more thing: you can even run two actuators with the came circuit using a dual H bridge.
3. But wait, I still have to build the same old circuit, but with an H bridge instead of a MOSFET
Enter the H bridge breakout board, which includes all the power conditioning circuitry I’d rather not build.
I’m currently evaluating two models, each based on popular H bridge chips:
Adafruit’s TB6612 breakout is tiny, cheap, and uses a really excellent chip. The TB6612 has built-in protection diodes, even, but it’s limited to ~1.2A output. (I also like Pololu’s TB6612FNG breakout.)
SainSmart’s L298N breakout uses a beefier chip with 2A output. It adds a ton of bells & whistles, like a heat sink, screw terminals, power switch, and indicator lights. For all this, it’s astonishingly cheap.
Left: TB6612. Right: L298N. Aren’t they handsome?
Back to the grind
Now that I’ve got a new Teensy LC soldered to some headers, it’s time to plug everything in and see what happens next.