In Part 1 I described the hardware components and the functionality of the LED clock. This this part, I’ll explore the software required to implement the functionality and seamlessly manage the different user interfaces.
I wanted a create a simple project to test a few ideas and still be useful in its own right. Walking through my local IKEA store, I saw a really inexpensive analog clock (Rusch) and decided that it would provide the right vehicle for what I had in mind.
A logic analyzer is an electronic instrument that captures and displays multiple signals from a digital system or circuit on a common time base. It is a really useful tool for debugging circuits and communications links. However, the cost of brand-name logic analyzers runs into hundreds of dollars and can be really hard to justify for hobby use.
Fortunately, there is a low cost alternative using open source software and inexpensive hardware.
In the first part of this blog I described building a test apparatus that allows me to experiment with tuning a PID loop controlling a levitating pin pong ball in a tube.
This second installment is about trying different hands-on methods of tuning the loop, understanding how they are derived, and how well they perform compared to each other.
PID (Proportional, Integral, Derivative) control is a classic control algorithm that I have used for a few projects, ending with ‘good enough’ control, without really spending time learning how to properly tune the PID constants.
Time for me to fill in the gap in my knowledge, so in this two part blog I want to capture my learning. Hopefully it is useful for someone else. In this first part I will document the learning and testing rig and software. The next part will be about tuning the control loop.
An ongoing question on many Arduino forums is the adaptation of software to the different types of matrix modules. Usually the poster has tried some LED matrix software and the display is reversed or upside down, or animations are disjointed across the module boundaries.
There are clear reasons this happens, and the Parola library has software configuration parameters that allow you to adapt how the software operates to suit your hardware module.
Once I had some hardware to test with, the next steps were to work out how to get a program onto the ATTiny and how to write efficient code. As 1kb of flash memory is not much to play with, space efficiency was a likely programming challenge!
In some upcoming projects I intend to embed some processing intelligence into small devices. The smaller Arduino boards are too big and expensive for these applications.
After some investigation, I settled on using the ATTiny series of 8 pin microcontrollers. These processors vary in capability (from a very low end) and all provide 6 I/O ports. Tools compatible with the Arduino ecosystem are also available.
As a first step, I designed a small breakout board for the SOP8 version of these MCUs.
I always seemed to get a clash between the device select signal (SS) on my SD/microSD card reader and some other Arduino hardware I was trying to run with it. To get around this I decided to make a dedicated SD card shield with a jumper selectable SS signal.
SS signal clashes are now a thing of the past!
One of the nice aspects of Arduino compatible hardware is the ease of program downloads. This is, in part, due to the bootloader that is programmed into the controller. How does that bootloader get on the hardware in the first place?
One answer is that a second Arduino can be used to load the bootloader (or any other stand-alone code) into the ‘virgin’ target hardware. The Arduino IDE includes an example program called ArduinoISP used for this, but it helps to have some supporting hardware. I built a shield with a few connections that speeds up the process of programming controllers.