New Comments System (please help me test it)

Stephane Boucher October 4, 201618 comments

I thought it would take me a day or two to implement, it took almost two weeks...

But here it is, the new comments systems for blogs, heavily inspired by the forum system I developed earlier this year.  

Which means that:

  • You can easily add images, either by drag and drop or through the 'Insert Image' button
  • You can add MathML, TeX and ASCIImath equations and they will be rendered with Mathjax
  • You can add code snippets and they will be highlighted with highlights.js
  • You can edit...

NXP LPC17xx/40xx: Decoding the Part ID

Ricky Bennett August 25, 20161 comment

This is the first blog of a number dealing with the NXP LPC17xx/40xx processor families and how to program them despite the lack of documentation.  The next blog will deal with implementing the LPC17xx/40xx UART with interrupts properly, and a subsequent blog will show how to use the UART in RS485 Normal Multidrop Mode (NMM) with Auto Address Detection (AAD).

My company has decided on using the NXP LPC17xx/40xx processor line for all our embedded projects.  Since...


Use DPLL to Lock Digital Oscillator to 1PPS Signal

Michael Morris July 24, 20162 comments
Introduction

There are occasions where it is desirable to lock a digital oscillator to an external time reference such as the 1PPS (One Pulse Per Second) signal output from a GPS receiver. One approach would be to synchronize a fixed frequency oscillator on the leading edge of the 1PPS signal. In many cases, this will result in adequate performance. However, in situations where simple synchronization does not provide adequate performance, digital phase-lock techniques can be applied to a...


The habitat of hardware bugs

Yossi Kreinin July 13, 20162 comments

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...


Digital PLL's -- Part 2

Neil Robertson June 15, 2016

In Part 1, we found the time response of a 2nd order PLL with a proportional + integral (lead-lag) loop filter.  Now let’s look at this PLL in the Z-domain [1, 2].  We will find that the response is characterized by a loop natural frequency ωn and damping coefficient ζ. 

Having a Z-domain model of the DPLL will allow us to do three things:

Compute the values of loop filter proportional gain KL and integrator gain KI that give the desired loop natural frequency and...

From Baremetal to RTOS: A review of scheduling techniques

Jacob Beningo June 8, 201616 comments

Transitioning from bare-metal embedded software development to a real-time operating system (RTOS) can be a difficult endeavor. Many developers struggle with the question of whether they should use an RTOS or simply use a bare-metal scheduler. One of the goals of this series is to walk developers through the transition and decision making process of abandoning bare-metal thinking and getting up to speed quickly with RTOSes. Before diving into the details of RTOSes, the appropriate first step...


Choosing a Microcontroller for Your Vehicle

Ed Nutter June 7, 20161 comment

There are many things to take into consideration when choosing a microcontroller or microprocessor for your autonomous vehicle.

Voltage

Some processors run on 5V and others use 3.3V.  Be sure to check the documentation before you buy.  Make sure your supply has a high enough amp rating that your microcontroller doesn't lose pwer.

Power

Can the system run using batteries?  Large, automotive sized vehicles can be run from large batteries or inverters in the vehicle.  Smaller...


Digital PLL's -- Part 1

Neil Robertson June 7, 20167 comments
1. Introduction

Figure 1.1 is a block diagram of a digital PLL (DPLL).  The purpose of the DPLL is to lock the phase of a numerically controlled oscillator (NCO) to a reference signal.  The loop includes a phase detector to compute phase error and a loop filter to set loop dynamic performance.  The output of the loop filter controls the frequency and phase of the NCO, driving the phase error to zero.

One application of the DPLL is to recover the timing in a digital...


Best Firmware Architecture Attributes

Dr. Tayyar GUZEL June 4, 20165 comments

Architecture of a firmware (FW) in a way defines the life-cycle of your product. Often companies start with a simple-version of a product as a response to the time-to-market caveat of the business, make some cash out of the product with a simple feature set. It takes only less than 2-3 years to reach a point where the company needs to develop multiple products derived from the same code base and multiple teams need to develop...


Choosing a Vehicle

Ed Nutter May 25, 20163 comments

There are a few things to take into consideration when choosing a vehicle or chassis for your autonomous vehicle. You can design and build your own, buy a stripped robot chassis, or use a radio controlled (RC) vehicle as a starting point. I usually use an RC vehicle as a starting point.

Two basic styles of RC vehicles exist. The first, is the toy-grade vehicle. It can be found in most retail stores, and usually costs below 50 dollars. Its main advantage is the low price, which can be as low...


Introduction to Microcontrollers - Timers

Mike Silva September 28, 20132 comments

Timers - Because "When" Matters

Computer programs are odd things, for one reason because they have no concept of time.  They may have the concept of sequential execution, but the time between instructions can be essentially any number and the program won't notice or care (unless assumptions about time have been built into the program by the programmer).  But the real world is not like this.  In the real world, especially the real embedded world,...


Two Capacitors Are Better Than One

Jason Sachs February 15, 20155 comments

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...


Unit Tests for Embedded Code

Stephen Friederichs March 6, 201411 comments

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...


Delayed printf for real-time logging

Yossi Kreinin October 25, 20133 comments

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...


Which MOSFET topology?

Jason Sachs September 2, 20119 comments

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

Stephen Friederichs January 18, 20145 comments

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...


Understanding and Preventing Overflow (I Had Too Much to Add Last Night)

Jason Sachs December 4, 2013

Happy Thanksgiving! Maybe the memory of eating too much turkey is fresh in your mind. If so, this would be a good time to talk about overflow.

In the world of floating-point arithmetic, overflow is possible but not particularly common. You can get it when numbers become too large; IEEE double-precision floating-point numbers support a range of just under 21024, and if you go beyond that you have problems:

for k in [10, 100, 1000, 1020, 1023, 1023.9, 1023.9999, 1024]: try: ...

Another 10 Circuit Components You Should Know

Jason Sachs October 30, 20131 comment

It's that time again to review all the oddball goodies available in electronic components. These are things you should have in your bag of tricks when you need to design a circuit board. If you read my previous posts and were looking forward to more, this article's for you!

1. Bus switches

I can't believe I haven't mentioned bus switches before. What is a bus switch?

There are lots of different options for switches:

  • mechanical switch / relay: All purpose, two...

How to Estimate Encoder Velocity Without Making Stupid Mistakes: Part II (Tracking Loops and PLLs)

Jason Sachs November 18, 201310 comments

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...