Ten Little Algorithms, Part 6: Green’s Theorem and Swept-Area Detection
Other articles in this series:
- Part 1: Russian Peasant Multiplication
- Part 2: The Single-Pole Low-Pass Filter
- Part 3: Welford's Method (And Friends)
- Part 4: Topological Sort
- Part 5: Quadratic Extremum Interpolation and Chandrupatla's Method
This article is mainly an excuse to scribble down some cryptic-looking mathematics — Don’t panic! Close your eyes and scroll down if you feel nauseous — and...
Going back to Germany!
A couple of blog posts ago, I wrote that the decision to go to ESC Boston ended up being a great one for many different reasons. I came back from the conference energized and really happy that I went.
These feelings were amplified a few days after my return when I received an email from Rolf Segger, the founder of SEGGER Microcontroller (check out their very new website), asking if I would be interested in visiting their headquarters...
ESC Boston's Videos are Now Up
In my last blog, I told you about my experience at ESC Boston and the few videos that I was planning to produce and publish. Here they are, please have a look and any feedback (positive or negative) is appreciated.
Short HighlightThis is a very short (one minute) montage of some of the footage that I shot at the show & conference. In future shows, I absolutely need to insert clips here and there of engineers saying a few words about the conference (why they...
How to Give Persistent Names To USB-Serial Devices on Ubuntu 14.04
If you have a bunch of USB-serial devices connected to your dock station and you needed to bind your USB-serial devices under static names so that all the USB-serial devices don't get to be assigned to random names by "udev" manager when you re-plug your laptop to the dock station, follow the instructions below. I will share the udev rules I created as a reference and give the step by step instructions to achieve persistent naming. All the steps worked on my Ubuntu 14.04...
Tenderfoot: Introduction to Magic (Numbers that is...)
Once upon a time, while participating in a source code review, I stumbled across the following C code in a header file:
struct Foo { //various structure fields char string_buffer[45+3]; //buffer requires about 45 bytes };My right eyebrow raised, I took a note, and continued with the code review, only to later stumble into this line of code in the body of a C function:
char * temp_string_buffer = (char*) malloc(45+3);Again, I took a note on this function, and continued...
Back from ESC Boston
NOT going to ESC Boston would have allowed me to stay home, in my comfort zone.
NOT going to ESC Boston would have saved me from driving in the absolutely horrible & stressful Boston traffic1.
NOT going to ESC Boston would have saved me from having to go through a full search & questioning session at the Canada Customs on my return2.
2017/06/06 update: Videos are now up!So two days...
Donald Knuth Is the Root of All Premature Optimization
This article is about something profound that a brilliant young professor at Stanford wrote nearly 45 years ago, and now we’re all stuck with it.
TL;DRThe idea, basically, is that even though optimization of computer software to execute faster is a noble goal, with tangible benefits, this costs time and effort up front, and therefore the decision to do so should not be made on whims and intuition, but instead should be made after some kind of analysis to show that it has net...
Launch of Youtube Channel: My First Videos - Embedded World 2017
I went to Embedded World 2017 in Nuremberg with an ambitious plan; I would make video highlights of several exhibits (booths) to be presented to the *Related sites audience. I would try to make the vendors focus their pitch on the essential in order to produce a one to three minutes video per booth.
So far my experience with making videos was limited to family videos, so I knew I had lots of reading to do and lots of Youtube videos and tutorials to watch. Trade shows are...
Intel 8088 - A blast from the past
The Intel 8088 is an 8 bit processor related to the 16 bit 8086.
The Microcomputer class consisted of wire-wrapping the chips to perfboard using sockets.I had taken computers apart, soldered, etc., but had never used wire-wrapping to construct a computer board to that point.Most people carried the board to class. A few people stared when I opened the plywood box with breadboard area, and plugged the full-sized power supply in. The lid is wide enough to hold the 11x17 paper the...
Zebras Hate You For No Reason: Why Amdahl's Law is Misleading in a World of Cats (And Maybe in Ours Too)
I’ve been wasting far too much of my free time lately on this stupid addicting game called the Kittens Game. It starts so innocently. You are a kitten in a catnip forest. Gather catnip.
And you click on Gather catnip and off you go. Soon you’re hunting unicorns and building Huts and studying Mathematics and Theology and so on. AND IT’S JUST A TEXT GAME! HTML and Javascript, that’s it, no pictures. It’s an example of an
Introduction to Microcontrollers - Button Matrix & Auto Repeating
Too Many Buttons, Not Enough Inputs
Assigning one GPIO input to each button can use up a lot of GPIO pins. Numeric input requires at least 10 buttons, plus however many additional control or function buttons. This can quickly get expensive, GPIO pin-wise, and also connector-wise if the keypad is off the uC PCB as it often would be. A very common response to this expense is to wire buttons (keys, etc) in a matrix. By connecting our buttons in an...
Byte and Switch (Part 1)
Imagine for a minute you have an electromagnet, and a microcontroller, and you want to use the microcontroller to turn the electromagnet on and off. Sounds pretty typical, right?We ask this question on our interviews of entry-level electrical engineers: what do you put between the microcontroller and the electromagnet?We used to think this kind of question was too easy, but there are a surprising number of subtleties here (and maybe a surprising number of job candidates that were missing...
How to Build a Fixed-Point PI Controller That Just Works: Part II
In Part I we talked about some of the issues around discrete-time proportional-integral (PI) controllers:
- various forms and whether to use the canonical form for z-transforms (don't do it!)
- order of operation in the integral term: whether to scale and then integrate (my recommendation), or integrate and then scale.
- saturation and anti-windup
In this part we'll talk about the issues surrounding fixed-point implementations of PI controllers. First let's recap the conceptual structure...
An overview of Linux Boot Process for Embedded Systems
This Text provides an insight in to the Embedded Linux Boot Process. Reader should have a basic Knowledge of Boot Process in general and should be familiar with Embedded Linux Boot Process.
.................PART-A................(1) Software components Involved in Embedded Linux Boot Process (a) Bootloader (b) kernel Image (c) root file system - either an initrd image or a NFS location(2) Steps during Booting process of a conventional...Introduction to Microcontrollers - More On GPIO
Now that we have our LED Blinky program nailed down, it's time to look more closely at outputs, add button/switch inputs, and work with reading inputs and driving outputs based on those inputs.
It's ON - No, It's OFF - No, It's ON...I have to confess, I cheated. Well, let's say I glossed over something very important. In our LED Blinky program, we never cared about whether an output '1' or an output '0' turned on the LED. Since we were just...
Introduction to Microcontrollers - 7-segment displays & Multiplexing
Doing the 7 Segment ShuffleThe 7 segment display is ubiquitous in the modern world. Just about every digital clock, calculator and movie bomb has one. The treadmills at my gym have 6 or 7, each one displaying 3 or 4 digits. What makes the 7-seg interesting is that it presents an opportunity to make a trade off between GPIO (output pins) for time. Every 7-seg display requires 8 outputs (the 7 segments and usually either a decimal point or a...
Ten Little Algorithms, Part 3: Welford's Method (and Friends)
Other articles in this series:
- Part 1: Russian Peasant Multiplication
- Part 2: The Single-Pole Low-Pass Filter
- Part 4: Topological Sort
- Part 5: Quadratic Extremum Interpolation and Chandrupatla's Method
- Part 6: Green’s Theorem and Swept-Area Detection
Last time we talked about a low-pass filter, and we saw that a one-line...
Which MOSFET topology?
A recent electronics.StackExchange question brings up a good topic for discussion. Let's say you have a power supply and a 2-wire load you want to be able to switch on and off from the power supply using a MOSFET. How do you choose which circuit topology to choose? You basically have four options, shown below:
From left to right, these are:
High-side switch, N-channel MOSFET High-side switch, P-channel MOSFET Low-side switch, N-channel...How to Give Persistent Names To USB-Serial Devices on Ubuntu 14.04
If you have a bunch of USB-serial devices connected to your dock station and you needed to bind your USB-serial devices under static names so that all the USB-serial devices don't get to be assigned to random names by "udev" manager when you re-plug your laptop to the dock station, follow the instructions below. I will share the udev rules I created as a reference and give the step by step instructions to achieve persistent naming. All the steps worked on my Ubuntu 14.04...
Padé Delay is Okay Today
This article is going to be somewhat different in that I’m not really writing it for the typical embedded systems engineer. Rather it’s kind of a specialized topic, so don’t be surprised if you get bored and move on to something else. That’s fine by me.
Anyway, let’s just jump ahead to the punchline. Here’s a numerical simulation of a step response to a \( p=126, q=130 \) Padé approximation of a time delay:
Impressed? Maybe you should be. This...
Unit Tests for Embedded Code
I originate from an electrical engineering background and my first industry experience was in a large, staid defense contractor. Both of these experiences contributed to a significant lack of knowledge with regards to software development best practices. Electrical engineers often have a backwards view of software in general; large defense contractors have similar views of software and couple it with a general disdain for any sort of automation or ‘immature’ practices. While there...
PID Without a PhD
I both consult and teach in the area of digital control. Through both of these efforts, I have found that while there certainly are control problems that require all the expertise I can bring to bear, there are a great number of control problems that can be solved with the most basic knowledge of simple controllers, without resort to any formal control theory at all.
This article will tell you how to implement a simple controller in software and how to tune it without getting into heavy...
Introduction to Microcontrollers - Buttons and Bouncing
What Is A Button?To your hardware, that is. As discussed in Introduction to Microcontrollers - More On GPIO, a button (or key, or switch, or any form of mechanical contact) is generally hooked up to a microcontroller so as to generate a certain logic level when pushed or closed or "active," and the opposite logic level when unpushed or open or "inactive." The active logic level can be either '0' or '1', but for reasons both historical and electrical, an...
Which MOSFET topology?
A recent electronics.StackExchange question brings up a good topic for discussion. Let's say you have a power supply and a 2-wire load you want to be able to switch on and off from the power supply using a MOSFET. How do you choose which circuit topology to choose? You basically have four options, shown below:
From left to right, these are:
High-side switch, N-channel MOSFET High-side switch, P-channel MOSFET Low-side switch, N-channel...Implementing State Machines
State machines are a great way to design software but they can be difficult to implement well.To illustrate this I’ll develop a simple state machine then increase the complexity to demonstrate some of the difficulties
We’ve all washed dishes before - it’s easy isn’t it? Scrub, rinse, dry, scrub, rinse dry. Scrub the dish until all of the gunk is off of it, rinse until the soap is off, put it in the drying rack. If you want to design software to implement this you have options. You...
How to Estimate Encoder Velocity Without Making Stupid Mistakes: Part II (Tracking Loops and PLLs)
Yeeehah! Finally we're ready to tackle some more clever ways to figure out the velocity of a position encoder. In part I, we looked at the basics of velocity estimation. Then in my last article, I talked a little about what's necessary to evaluate different kinds of algorithms. Now it's time to start describing them. We'll cover tracking loops and phase-locked loops in this article, and Luenberger observers in part III.
But first we need a moderately simple, but interesting, example...
The habitat of hardware bugs
The Moscow apartment which little me called home was also home to many other creatures, from smallish cockroaches to biggish rats. But of course we rarely met them face to face. Evolution has weeded out those animals imprudent enough to crash your dinner. However, when we moved a cupboard one time, we had the pleasure to meet a few hundreds of fabulously evolved cockroaches.
In this sense, logical bugs aren't different from actual insects. You won't find...
Delayed printf for real-time logging
You often debug by adding a few printfs and looking at the logs. In some real-time/low-level contexts though, you don't have time for text formatting.
You don't want prints to affect timing too much, because then timing-related bugs you're chasing might disappear. And you certainly don't want the system to stop functioning altogether because prints cause it to miss real-time deadlines.
A common alternative to prints is more "raw" logging - an event buffer, where event is a union keeping...
Two Capacitors Are Better Than One
I was looking for a good reference for some ADC-driving circuits, and ran across this diagram in Walt Jung’s Op-Amp Applications Handbook:
And I smiled to myself, because I immediately remembered a circuit I hadn’t used for years. Years! But it’s something you should file away in your bag of tricks.
Take a look at the RC-RC circuit formed by R1, R2, C1, and C2. It’s basically a stacked RC low-pass filter. The question is, why are there two capacitors?
I...
Ten Little Algorithms, Part 3: Welford's Method (and Friends)
Other articles in this series:
- Part 1: Russian Peasant Multiplication
- Part 2: The Single-Pole Low-Pass Filter
- Part 4: Topological Sort
- Part 5: Quadratic Extremum Interpolation and Chandrupatla's Method
- Part 6: Green’s Theorem and Swept-Area Detection
Last time we talked about a low-pass filter, and we saw that a one-line...
