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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Circuit Python adds Python to Microcontrollers

Add rapid prototyping to your rapid prototyping board with Circuit Python or MicroPython

CircuitPython Matrix

Back in 2013, a Kickstarter ran for a project to put a python interpreter on a microcontroller. At the time I could not see the benefit. Cool project, but I asked myself: “why?” On my last Adafruit order, I received a free Circuit Playground Express. The board comes with CircuitPython pre-installed. After playing with Circuit Python, or CP, I finally “get it.”

For Valentine’s Day, I made an animated LED heart for a new love in my life, Circuit Python. Well, love is a bit of a strong word. The past couple of weeks I have been learning Circuit Python, and I am excited by what it offers.

What is Circuit Python?

It is a Python implementation that runs on microcontrollers. The code exists on the microcontroller as text. The interpreter runs the code from that text file. Circuit Python is built on, or based on, MicroPython. Adafruit is designing it to teach programming. It is easy to get started, just open up the code.py file from the auto-mounted drive and start typing. When you hit save, the code runs. That’s it.

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When it is time to move away from delay(), it’s time to learn how to properly use millis(). If you’ve had trouble following my millis() examples, maybe a live tutorial will help.

In this AddOhms Livestream, I go through 4 code examples:

1. Blink, the one with delay(), as a starting point.

2. Blink Without Delay, line by line, what is it doing

3. PWM Fading without delay() (and with buttons)

4. Binary counter that uses buttons to speed up and slow down.

Appearance:Live millis() tutorial: AddOhms Live #5
Outlet:AddOhms Voideo Tutorials
Location:YouTube
Format:Vlog

7 Arduino LCD display tips and tricks

Character LCD tutorial broken down by simple tips

Arduino LCD display

When I started working on Open Vapors, I thought the stumbling point would be the PID algorithm or safe AC line control. However, it turned out; I spent a significant amount of time understanding how to print to the Arduino LCD display correctly.

As I dig into my latest project, the lessons I learned back then are coming back to me. Here are 7 tips for driving an Arduino LCD display, like one with 2×20 or 4×20 characters.

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PWM a 3-pin PC fan with an Arduino

Note: 4-pin fans already have a PWM signal

Aeroscope Measuring a Fan

A question came up on IRC regarding how to PWM a 3-pin PC fan with an Arduino using analogWrite(). Controlling the fan was seemingly straightforward. The problem was that the hall effect sensor, or TACH signal, was incredibly noisy. The noise made it impossible to measure the fan’s rotation. Working through the question, I found three issues to tackle:

  1. You need to use a PNP transistor
  2. Filter capacitors help
  3. Create a non-blocking RPM measurement (with millis())

This post addresses all three issues regarding how to PWM a 3-pin PC fan with an Arduino.

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Soft Power Controller State Machine

Here's the logic behind the Pi Soft Power Controller

RPSPC State Machine

Previously I looked at the hardware needed to build a Raspberry Pi soft power supply. This week I’m looking the state machine for the microcontroller. Why is such a complicated circuit necessary? I am replacing a Super Famicom (SNES) motherboard with the Pi. The trick is, I want to use the original power switch to turn the Pi on and off.

This requirement presents a problem. When the switch goes into the “OFF” position, power needs to stay on long enough for the Pi to properly shutdown. So the switch itself can’t provide power to the Pi directly. With minor changes, the code in this state machine could be made to work with push buttons as well. If I add that feature in the future, I’ll update the code on the RPSPC GitHub project.

Before continuing with the state machine, first I need to thank all the mailing list members. You guys really rock. When I asked for state machine diagraming tool suggestions, you guys sent me enough options for an entire (future) post to compare them. 

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Arduino Data Logger: Serial Monitor Alternatives

Forget the serial monitor, here's 5 other ways to do Arduino data logging

arduino data logger options

The Arduino serial monitor is usable when you want to watch data from an Arduino. However, it does not have a built-in method for saving the data. Here are some ideas if you want to build an Arduino data logger with or without a PC.

Important note on Arduino Data Logger examples

With all of these examples, please remember that whenever you open the Arduino’s serial port, the board will reset. So if your log file shows “Initializing SD card…” with a few data lines in between, it is because there is a reset happening.

Initializing SD card…initialized.
Temp: 34, Time: 03:24:44
Temp: 33, Time: 03:24:45
Temp: 34, Time: 03:24:46
Tem

Initializing SD card…initialized.
Temp: 34, Time: 03:24:50
Temp: 34, Time: 03:24:51
Temp: 33, Time: 03:24:52
Temp: 34, Time: 03:24:53

In that code you can see data logging started and then restarted. What happened is that after programming, the board starts logging. Then when you open the Serial Monitor, the data logger restarts.

To solve this issue, either disable auto-reset, add a 3-4 second delay at the start of setup(), wait for a character to be received, or wait for a button press. That will give you time to open the Serial Monitor.

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Sending simple serial commands to an Arduino

Don't send words when characters will do

sending simple serial commands arduino

Sending simple serial commands to an Arduino is the easiest way to communicate between an Arduino and a computer. The computer could be a PC, a Raspberry Pi, or any device that communicates with serial.

By sending and “decoding” a single character it is easy to add a simple debug menu or even serial menu. Plus, it is easy to extend.

Single Character vs. Full Words

The mistake I see many people make is that they try to send full-text strings as serial commands. For example, to turn on a LED, I have seen (silly) commands like “RED LED ON” or “RED LED OFF.” While you could use something like strcmp(), as I showed on the Multiple MQTT Topics example, that tends to be overkill for most serial commands.

Humans like words, computers like binary. Just send one character over serial.

switch (variable) {
  case ‘a’:
	// A Stuff

  case ‘b’:
  case ‘c’:
	// B and C Stuff
  break;
}

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Multiple MQTT Topics with Arduino PubSubClient

Adding a few more subscriptions is pretty easy.

multiple mqtt topics

In my Arduino MQTT Examples, I kept things simple by only subscribing to a single topic. One of the strengths of MQTT is that a device can subscribe (or publish) to multiple topics. The broker will sort things out. Even though my first example only showed one, it is straight forward to get the Arduino PubSubClient library to subscribe to Multiple MQTT topics.

The quick answer is that you need to look at the MQTT response to find out which topic sent the payload.

tl;dr version

If you’re looking for a quick answer, here’s the magic code we’ll add to the callback() function.

void callback(char* topic, byte* payload, unsigned int length) {
if (strcmp(topic,"pir1Status")==0)
  // whatever you want for this topic
}

Keep reading for a more detailed explanation of how to Subscribe to Multiple MQTT topics with Arduino’s PubSubClient. Obviously, this code will work on Arduino boards with a TCP/IP interface and, of course, the ESP8266 based boards.

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