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Quorten Blog 1

First blog for all Quorten's blog-like writings

So, I was studying my motor control designs, and it came to my mind: When I am controlling motors, don’t I need larger decoupling capacitors on the motor power supply path? I remember when just taking a crack open at the Lego MINDSTORMS RCX programmable brick, I saw four very large electrolytic capacitors. Surely, three of those were devoted just to the three available motors you could drive, and the fourth was for the board-level power supply. Surely, what I’ve seen about the absolute basic schematics.

And indeed, I am in agreement with the expert advice. Here is a great discussion about the subject on this Arduino forum. Use 100 nF ceramic for decoupling the logic power supply, and 100/470 uF electrolytic plus 100 nF ceramic to decouple the motor power supply. Yes, indeed the Raspberry Pi schematics that show just the L293D directly connected from the Raspberry Pi to the motor are too simple.

20200307/DuckDuckGo L293D decoupling capacitors
20200307/https://forum.arduino.cc/index.php?topic=293864.0

Also, I learned about another curious tidbit. If you are wiring up sensitive analog circuits, you may also need inductors to decouple your circuit. For digital, inductors are generally overkill and not needed for sufficient decoupling. That’s good… go easy on the novices, come on!

Oh, another thing I should note after having looked around… cheap analog to digital conversion with a variable resistor? You don’t even need a 555 timer chip for one-shot RC network timing. Thanks to GPIO being able to be switched between both input and output, you can just wire up a capacitor directly to your variable resistor. You switch the pin to output to charge it, then switch to input to measure the time to discharge it. You get a comparator and a voltage sink for free. Where does the voltage sink come from? It comes from the built-in pull-down resistor, that’s why you can get it to work with so little glue logic.

A prime use in portable applications is, of course, a battery voltage indicator circuit. When the battery voltage runs low, you know you don’t have much time left until your next recharge or battery replacement.