Tagged: arduino

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Bigger is better: Build an Arduino-powered monster scrolling LED sign for about $15 a foot


Would you do with a massive full color animated LED display? How about…

  • Read your Tweets in giant 140 char gulps from a block away
  • Add English sub-titles to the Eiffel Tower
  • Display a live-updating, 45 digit long countdown of the number of atoms left in the known universe

What if you could build the display however long you needed it, for only about $15/foot?

What if it was really easy to build and used everyone’s favorite low cost micro-controller so you could easily change the software to do whatever you wanted?

Well you can! Read on for details and perfunctory video!

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Blindsend chart

Getting Real – Using Blind Send SPI to Turbocharge the Adafruit DotStar Libraryspi,

Last time, we experimented with spiritual blind-sending as a way to theoretically speed up SPI on AVR. While there were lots of fancy oscilloscope traces and impressive demo code, there is nothing like an actual, real, practical application to get people excited. Read on to see how much faster we can make the already highly optimized AdaFruit DotStar library with a little blind-sending action… (spoiler alert – the answer is lots more faster!)
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SPI with a Blindfold On- speed up by letting go and trusting the machine

Constantly checking to see if the coast is clear feels responsible, but it wastes cycles. Sometimes it is better to leap (or load) without looking. With a little hand-coded assembly, we can run our AVR processor lock-step with the SPI hardware and blindly dump new bytes into it at precisely the right moment. Because we don’t spend any time reading and testing status bits, we can increase the maximum throughput by more than 20%. If the prospect of screamingly fast yet perfectly safe SPI turns you on, read on…
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AVR Timer-based One Shot Explained

Last time, we made one-shot pulses using the AVR’s built in hardware timer module. Today we are going to dive deep into the datasheets to see how this technique is able to coax the normally free-running timer into generating a single pulse. Along the way, we will learn about the low level rules that govern the operation of the timer, and use a trick or two to get around those rules. Read on!…

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The Perfect Pulse- generating precise one-shots on AVR8

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It is possible to generate one-shot pulses on an AVR that…

  1. Are as narrow as a single clock cycle (63 nanoseconds!)
  2. Are precise to a single clock cycle
  3. Will run to correct completion no matter what else the processor is doing 1
  4. Do not require you to turn off interrupts at all (!)
  5. Do not require any assembly code

These pulses are generated in pure hardware. They require a couple of instructions of interruptible code to fire. Once fired, they are completely autonomous and depend only on the system clock to run to completion.

Sound cool? Read on!

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Save the Earth One Resistor at a Time – External pull-up resistor no longer needed for DS18B20 temp sensor


Using the updated Arduino 1-Wire library code presented here, you can eliminate the need for an external pull-up resistor for typical small networks of DS18B20 temperature sensors.  This should also work with any AVR processor and other types of 1-Wire devices as well. You can download the updated 1-Wire library here…


The mythical “required” external pull-up

From the DS18B20 Data Sheet

From the DS18B20 Data Sheet

If you’ve ever used the ubiquitous (and amazingly useful!)  DS18B20 family of 1-Wire temperature sensors, you’ve almost certainly used a 4.7K ohm pull-up resistor as well. Every one of the seemingly endless Arduino DS18B20  tutorials on the web starts with some version of the line “You will not be able to do anything with this senor until you go out and procure yourself a 4.7K ohm resistor”. AdaFruit is even generous enough to include one of these resistors with every DS18B20-based temperature sensor they sell (be it bare, waterproof, or hi-temp) because they know you are going to need it.

I am here to tell you that everything is about to change. If you were banking on your stockpiles of 4.7K ohm resistors to be the one reliable store of value in these uncertain times, you need to rethink your long-term asset preservation strategy because the decade-long run of stable demand for this part is about to plummet. Yes – it is now possible to connect DS18B20 sensors without any external pull-up resistor at all!

Outrageous claims demand outrageous proof, so let’s start with a brief demo that proves beyond a shadow of a doubt that this is not just a cockamamie theory, but cold hard fact…

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Temperature Logging to a Google Spreadsheet with an Arduino Yun

UPDATE 8/7/2104:It appears that Google occasionally will randomly and silently drop the authorization for an Apps Script web app. If you notice that your spreadsheet has stopped updating and you know that your logger is still working, then you probably need to log into your spreadsheet from a web browser, go into the scripts editor, and manually execute any function in the script. This will cause a popup that will reauthorize the script and everything will then start working again.

I think this is the last straw. I can not recommend using Google for logging (or any other non-trivial application) any more. This stuff is just too flaky. Sorry.

If you are like me, you often find yourself in a situation where you need to log multiple channels of temperature data. From testing nano-insulating paint to debugging an overheating geothermal well, most of us will have need of accurate and frequent temperature logs at some point in our short and brutish lives.

Here is a recipe to make a reliable, cheap, and easy cloud-based, multi-channel temperature logger using an Arduino Yun and DS18B20 temperature sensors. I chose the Yun because everyone loves Arduinos and this one can connect to the internets. I choose the DS18B20 sensors because they are awesome and cheap and accurate and you can hook up lots of them to a single pair of wires.

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