Arduino millis() plus addition does not add up

Here's why you should use subtraction with millis()

Arduino millis banner

In the past, I’ve covered how to reset Arduino millis() and have provided a growing list of examples using millis(). While reviewing the code for the elegoo Penguin Bot, I was reminded of a millis() mistake I see often: addition. The only way to properly handle millis() rollover is with subtraction. Let’s look at why (and how.)

What is Arduino millis()

The Arduino library has a function called millis() which returns the number of milliseconds the processor has been running. On other platforms, you might see references to a “tick counter.” It is the same idea. A hardware timer keeps incrementing a counter at a known rate. In this case, that rate is milliseconds.

A mistake new programmers often make is trying to “reset millis().” A better method is to compare two time-stamps based on millis(). So this if-statement is comparing a previous timestamp to the current value of millis().

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Penguin Bot from elegoo hands-on review of the kit build

Reviewing a dancing robot

Penguin Bot Black Red and Clear

Recently I received three packages from Elegoo Industries. They are a company based in Shenzhen China. Before those packages, I noticed there name several times on various electronics kits on Amazon. They asked me if I’d help them with a video that shows how to assemble their latest creation: Penguin Bot.

There is not much point in sharing that video with you unless you’ve purchased one. So instead, here is my review, or hands-on, of the kit. I will, however, show you a short Instagram video I made to show off Penguin Bot’s cuteness

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Learning to use a new oscilloscope can be daunting. In this video, I show 5 measurements you can make using just an Arduino as your DUT. Learn how to offset voltage, setup measurements, enable infinite persistence, save reference waveforms, AND trigger (and decode) serial signals. For this video, Rohde & Schwarz was kind enough to send me an RTM3004. This video is a follow-up from an ealier blog post which featured 6 scope measurements you can make with an Arduino.

Check out the AddOhms Episode 28 Show Notes for links related to the episode.

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Making tutorial videos and project videos is a very different process. It is very easy to script a tutorial. In fact, I think it is a necessary step. Project videos, on the other hand, are more organic. In this project, I build a capacitive activated coin bank, based on this Coin Acceptor from Adafruit. It uses an MSP430 to do capacitive sensing and then a Pryamiduino to control the rest of the electronics. In the end, I do some classic AddOhms special effects to demonstrate how the project works. For detailed notes and design files, hit the button below for the element14 project page.

Bank to the Future on e14

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Date:August 24, 2018
Appearance:Bank to the Future on element14 presents
Outlet:element14 Presents
Format:Vlog

Arduino MKR Vidor 4000 Hands-On

Is the Arduino FPGA worth buying?

Arduino MKR Vidor 4000 - Blue

Earlier this week, I looked at the Arduino MKR Vidor 4000 during an AddOhms live stream. My goal was to understand the Vidor better. It is the new FPGA-based Arduino which started shipping this month. It runs about $60. You can learn more at the Vidor Product Page on the Arduino website.

In this post, I briefly touch on the difference between an FPGA and a microcontroller. Then I walk you around the MKR Vidor 4000’s board. Using one of the examples, I talk a bit about how the various chips communicate with each other. This section also highlights what makes the Arduino FPGA board different from other development boards. Lastly, I answer “should you buy an Arduino MKR Vidor 4000?”

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As promised, the Arduino team shipped the MKR 4000 VIDOR by the end of July. The graphical editor is still missing in action, but you can check out the board now. I received mine. In this AddOhms Live Stream, I turned it on and checked it out.

This video is a “working” live stream. Generally, I try to set up some demos and run through some canned actions. Not this time. I used the board once, on another computer. You get to watch how I attack a new board…live! Warts and all.

Key things I check out:

  • How do you program the FPGA? (what does that even mean for the VIDOR.)
  • The VidorTestSketch (communicate between the SAMD21 and the Cyclone FPGA)
  • LogoDraw (the VIDOR draws the Arduino logo over HDMI)
  • The include files for each of the VIDOR libraries

I’m writing up my experience so far, along with what I’ve learned. Until then, click below to see the 1-hour live stream.

Watch Full Live Stream

This AddOhms episode is part 3 of the “design your own Arduino” series. In this one I populate a bare PCB, reflow solder it, debug a few issues, and load the Uno bootloader. Originally, I designed 2 versions of the board. One version contained an error that I planned to fix in the episode. Well, turns out, the “correct” board had two issues which were more interesting.

Check out the #27 show notes for links to a bunch of stuff in the episode, including the design files.

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Five Arduino math fixes for when it is wrong

Check these when your Arduino can’t math

Arduino Math

While the Arduino library does an excellent job of hiding some of C/C++’s warts, at the end of the day, it is still just C/C++. This fact causes a few non-intuitive issues for inexperienced programmers. When it looks like Arduino math is wrong, it is probably one of these reasons.

When people ask me for help with their programming, I check each of these Arduino math mistakes. If your code seems to be hitting a bug, check to make sure it is not how the compiler handles math.

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Arduino EEPROM stores any datatype

.get() and .put() make saving floats easy

Arduino EEPROM Hero 1600px

Funny how a simple idea can spider out into multiple paths. Arduino EEPROM seemed like a straightforward concept. A few a years ago it was as easy as having either 512 or 1024 bytes of flash memory. The Arduino IDE offered an EEPROM library which let you read and write a single byte. Today, however, with many different processor architectures saving data to EEPROM varies. It is now possible to save any datatype to EEPROM but not on all boards and not all using the same method.

While programming an coin accepter sold by Adafruit on an AddOhms live stream, I discovered two “new” methods in the Arduino library. At least, these functions are new to me! A couple of years ago EEPROM.get() and EEPROM.put() appeared. Using these functions, you can store any datatype in EEPROM.

This post covers tidgets related to using Arduino EEPROM to store any value across multiple boards, or platforms. Specifically boards such as the Uno, Nano, Mega, and Zero are covered. Additionally Arduino-compatible boards from Espressif, PRJC, and Adafruit are covered as well.

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