When programming in Arduino, you might have occasion to go beyond the standard datatypes of int and String. Data Types You might have noticed that if you did the following: int count = 5; int groups = 2; Serial.println(count/groups); Serial would have printed 3. This can be a head-scratcher, especially since we never had the occasion to use other data types. A data type refers to what the data can represent. This primarily has to do with int, which cannot represent decimal points. The solution is to use a float which is another data type, except that now it can handle floating point operations. For example, if we changed the example above a little: ...

While blinking LEDs can be really fun, wireless communication is like magic. The nRF24 is a all-in-one SMD IC for wireless communications. Chuck in an Arduino microcontroller and you got yourself a Arduino with a wireless link. The nRF24 has been adapted by Chinese manufacturers to produce an extremely inexpensive board that has very good characteristics. This chip costs $3 from Digikey, but it costs $1.37 on Aliexpress for a full board with a PCB antenna. Both through-hole and SMD versions of this board exists, making it easy to take from prototyping to board design. ...

Sometimes Arch Linux complains about missing keys, after spending a little too long Googling around, this was the solution: Upgrade archlinux-keyring first, then upgrade the rest of the system. sudo pacman -Sy archlinux-keyring If that doesn’t solve your problems, try switching your keyserver sudo nano /root/.gnupg/dirmngr_ldapservers.conf Change the keyserver line to: keyserver hkp://pgp.mit.edu:11371 as documented here: https://wiki.archlinux.org/index.php/Pacman/Package_signing#Cannot_import_keys Your system time might be wrong as well, so remember to check that. Sometimes when installing a tool, it says that a particular GPG key is outdated. This means that the tool is no longer maintained and a red flag. You might want to look for keys elsewhere.

The LM3914 is a dot/bar display driver. It senses analog voltage level and drives 10 LEDs, making it suitable for use as a power indicator, and there are a number of products that use this function. This device is marketed as a 2.4-20V power display indicator on Aliexpress and Banggood. It is a pretty small board, and would be useful in determining the charge on a acid battery or LiPo battery, where the voltage varies with the charge. ...

I had one of these lying around the house. It was bought for the windows and doors, but it was never used at my place. Operation The white package next to the alarm is a magnet, so this indicates that the alarm is operated by a reed-switch. When the door is opened, the magnet will move further away from the alarm. The changing magnetic field is detected by the alarm, and it starts a countdown. When the password is typed in, the countdown stops. If it is not typed in before the countdown completes, the alarm will buzz. ...

This error was frustrating to fix but turned out it was a teensy tiny error of my own. Context I was attempting to send a struct over a radio on Arduino struct State { int x; int y; }; struct State MyState; .... radio.send((uint8_t *)&MyState, sizeof(struct MyState)); So I tried to get the size of an instance instead of the struct itself. No wonder Arduino complained that it couldn’t find the struct with the error message of: invalid application ... to incomplete type 'loop()::MyState'. ...

This is how I hooked up an ST 7735 TFT LCD module to an Arduino. This is a small, cheap screen with color display, and an excellent Adafruit library has already been written for it, making it a breeze to use. I recently purchased a TFT screen with the intention of using it eventually. However the markings on the back confused me a little. These are the mappings from the generic red SPI TFT to the Adafruit breakout. ...

After messing around with the nRF52 for a little while, one day I wondered if there was a cheaper option for bluetooth modules, because all I really wanted was the Bluetooth from the nRF52. It took awhile to look, but I was not disappointed. I found the CC2541. Introduction HM-11 modules have been floating around for a very long time. Their latest claim to fame is their enlistment as credit card skimmers, as documented on Sparkfun’s investigation. I encourage you to read it, it is quite detailed and fascinating. ...

Tl;dr, don’t power Arduino Pro Mini Clones with 12V. You will see smoke. I was attempting to rebuild my Sunrise alarm clock with an Arduino Pro Mini. However when I plugged in my 12V supply, a capacitor exploded on the board. The brown bit that you see near the bottom of the board was the component that sparked, and then started to smoke. It smelt like solder. I pulled out the power supply, but I think the board is ruined. ...

A little desk thingy that can report the weather outside and serve as a Pomodoro timer. I call it the Able Stable. Background I often find myself checking on the weather before I go out. Sometimes the weather can be bitterly cold, and other times it can be warm enough to stroll in, but it is hard to tell just by looking out of the window. Since I work at my desk most of the time, it is useful to have productivity enhancing tools such as a Pomodoro timer nearby. ...