Raspberry-Pi on Lloyd Rochester's Geek Blog

GPIO Input with libgpiod

Mon, 10 May 2021 00:00:00 +0000

GPIO Input with libgpiod

We can use the libgpiod library to configure a GPIO line as input and read it’s value. We’ll create a switch circuit so we can test the value is a logic high or low. More info on libgpiod can be found in my libgpiod intro for installation and usage.

Here is a previous post to blink an LED using libgpiod.

Input Circuit

Into our Raspberry Pi we’ll use GPIO 4 and configure this pin as an input. We’re going to add some resistors to control the current into this circuit. When the switch is in one direction you can see current will essentially not flow.

Blinking an LED with libgpiod

Mon, 03 May 2021 00:00:00 +0000

Blinking an LED with libgpiod

In the previous post we introduced libgpiod. In this post we’ll use the command line tools to blink an LED. Finally, we’ll write some C code to blink the LED using the libgpiod library.

LED Driver Circuit

Skip this section if you already have a good circuit to drive an LED. A simple NPN Transistor is a cheap and robust LED drive that only requires two resistors.

Raspberry Pi SPI Explained

Wed, 21 Apr 2021 00:00:00 +0000

Raspberry Pi SPI Explained

This post attempts to provide some finer details when using SPI on Raspberry Pi as it pertains to using the Chip Select pins and multiple SPI Interfaces. Note, I will not use MOSI and MISO to ditch the old master/slave nomenclature and use SPO and SPI instead.

Here is a quick diagram which will be explained in the following sections.

The Basics of SPI on the Raspberry Pi

If you use raspi-config you can enable SPI.

Audio Clip Capture by Threshold

Sat, 10 Apr 2021 00:00:00 +0000

Audio Clip Capture by Threshold

Updated December 28th 2022

Here is a command line tool to capture audio clips based on two thresholds. Keep the tool running and it will write a number of audio files with audio that is loud enough for long enough. How loud and how long are the thresholds that are inputs to the program. For example we may want to record audio clips that only exceed 3 seconds. The loudness level is meant to keep us from recording noise.

LSM9DS1 Command Line Tool for Raspberry Pi

Wed, 03 Jun 2020 00:00:00 +0000

LSM9DS1 Command Line Tool for Raspberry Pi

I recently created a LSM9DS1 Command Line Tool for the Raspberry Pi. This tool was used to capture Accelerometer and Gyroscope data. I did an experiment to see what the readings look like, how the sensor behaves and the noise levels. This experiment is far from perfect but gives good insight and understanding.

Sensor Setup

The LSM9DS1 was taped to the tread of a \( 16" \)stroller tire. The location was directly on top of the tread so the wheel had to be spun up in the air. The wheel was parallel to the ground as the stroller was on it’s side. The axis of the Accelerometer had Z facing outward, X facing along the rotation of the wheel, and Y facing perpendicular to the rotation of the wheel.

UART Between Raspberry Pi and Arduino

Wed, 18 Mar 2020 14:02:54 +0000

Using a 2-wire serial connection we can communicate from a Raspberry Pi (RPi) to an Arduino. For the Raspberry Pi we’ll use the built in UART accessed through a tty, and the Arduino we’ll use the Serial Communication Library.

What this Example Does?

This example will use a RPi and Arduino to send a fixed message from the RPi to the Arduino. The Arduino will then echo what it receives back the RPi. The hardware used was a RPi B+ and the Arduino Due. The code is all in C/C++.

Raspberry-Pi on Lloyd Rochester's Geek Blog

GPIO Input with libgpiod

GPIO Input with libgpiod

Input Circuit

Blinking an LED with libgpiod

Blinking an LED with libgpiod

Table of Contents

LED Driver Circuit

Raspberry Pi SPI Explained

Raspberry Pi SPI Explained

The Basics of SPI on the Raspberry Pi

Audio Clip Capture by Threshold

Audio Clip Capture by Threshold

LSM9DS1 Command Line Tool for Raspberry Pi

LSM9DS1 Command Line Tool for Raspberry Pi

Sensor Setup

UART Between Raspberry Pi and Arduino

What this Example Does?