Wellys Dev

Where I demonstrate different methods of measuring a servo pulse to ensure it meets requirements.

Introduction

In the entry on servos I discussed the specific pulse requirements to make a servo move. In a nutshell, a servo needs a positive pulse .5ms to 2.3ms in a 60Hz signal. Or to put it another way, it requires a 60Hz signal with a duty cycle ranging from 3% to ~14%.

Where I use an example project from avr-gcc to better understand how to program the ATmega328.

Sources

• Microchip AVR ATmega328 Go to this page for the datasheet, you will need it.
• Definitive UNO pinout
• avr-libc Standard AVR C Library
• avr-libc: simple project The project which this entry will cover.

Introduction

In the previous entry, I wrote a C equivilent to the Arduino analogWrite(). The entry demonstrates the fundamental method of getting the ATmega328 to perform, is to program the registers. From here on, we’ll continue to expand on this approach.

Where I compare the Labrador with the $300 Digilent Analog Discovery 2 and determine if using a “rail-to-rail” operational amplifier matters.

Sources

• LM358 Datasheet
• OP484 Datasheet
• Analog Devices Op Amp Inputs, Outputs, Single-Supply, and Rail-to-Rail Issues
• Texas Instruments A Single-Supply Op-Amp Circuit Collection

Research

This video, Rail to Rail Op Amps P1 got me thinking as to the issues with the LM358. So to determine if it mattered on my previous amplifier design, I went back and redid the circuit. I used the OP484, as it was an op-amp I had and it is specifically a “Precision Rail-to-Rail Input and Output…”. I thought it would be interesting to do two things:

Where I use the Labrador to test a different way of implementing Blink on the RP2040 using timer().

Sources

• Raspberry Pi Pico Python SDK

Background

I started reading the Python SDK above and noticed this example on page 12.

Its a method of blinking the LED in the background, which allows the processor to do other work. Let’s try it and see how well it works using the Labrador.

Code

from machine import Pin, Timer

led = Pin(13, Pin.OUT)
tim = Timer()
def tick(timer):
    global led
    led.toggle()

tim.init(freq=50, mode=Timer.PERIODIC, callback=tick)

Where I begin to work with the Adafruit Feather RP2040 (Feather) and MicroPython (uP) and use the Labrador to test the board.

Using Blink Test to Confirm Board Works

Using an Interactive Pin Test to Confirm Header Works

Sources

• Adafruit Feather RP2040
• Raspberry Pi RP2040 Getting Started
• RP2040 Datasheet
• Arm: Raspberry Pi RP2040: Our Microcontroller for the Masses
• Get Started with MicroPython on Raspberry Pi Pico
• Raspberry Pi Pico Python SDK
• MicroPython RP2 Docs

Background

After being disappointed with the uP development for the ESP32, I thought it would be fun to try the latest and greatest, hottest, just out of design, the Raspberry Pi RP2040 Microcontroller. I was able to secure two Adafruit Feather versions and will use those to test.

Where I continue to use the Labrador to test the PWM functionality of the ESP32.

Sources

• Makeability Lab Lesson 3: Fading an LED with PWM
• ESP32-GetStarted: PWM
• MicroPython PWM
• Espressif: LED Control

Background

We continue to use the Labrador to evaluate how the HUZZAH32 operates. In this case, we’ll dive into how to use the H/W PWM functions as compared to doing it in software.

The PWM functionality is called LEDC by Espressif, the manufacturer of the ESP32. This stands for LED control and it works quite well for fading, controlling brightness etc of an LED. That said, we can understand it far better if we observe the signals using the Labrador.

Where I use the Labrador to test specific functions of the ESP32 running MicroPython.

Sources

• Quick reference for the ESP32
• ESP32-GetStarted
• Adafruit HUZZAH32
• ESP32-DevKitC I think this is the same as the HiLetGo version I have
• ESP32 Makeability Lab

Background

The best way to begin to understand a board is to play with it. In more technical terms, this means writing software and learning how the board responds. The higher the capability of the board, the greater the need for examining the board with high functioning tools. In our case, we are going to keep things very inexpensive, however, extremely capable and powerful.

Where I realize something important about using test equipment!

Big Learning!

The Labrador has a great price given its performance as a piece of test equipment. However, like all test equipment, it is important to understand and use it properly for testing any circuit. If the circuit under test isn’t responding properly, always check the test equipment along with the circuit.

In this case, I expressed a concern below that “At first, I thought I was finding the same issue as what I had with the Forth HAL version. Specific pins were failing the tests. However, what is happening is that the test i.e; HIGH to LOW, would take 10-12 seconds, while LOW to HIGH would take less than a second.”

Where I explore filters in electronics and use the Espotek Labrador to demonstrate how to understand filters and create amplitude response curves. This discussion will be absurdly simplistic in comparison to the topic. My goal is to show sufficient theoretical examples of filters, so we can then test them using the Labrador.

Video: How to Use the Espotek Labrador to Analyze a High Pass Filter Amplitude Response Curve

Our goal with the Labrador is to test the following filter analysis. Doing so will help make electronics more intuitive and familiar and help you understand as to how to use the Labrador. It will also help you understand how to plot data and in this case, using a log scale.

Using potentiometers for programmable bias and gain on the amplifier.

A Typical Problem

If you followed the last couple of experiments, AC Signal Analysis and DC Sweep, you know you have a functional amplifier that will take either a DC level or AC signal and amplify it -2.5x. How do you know this? You were able to test the amplifier using the Labrador’s built-in Signal Generator.

This is nice, if that is the only signal you want to amplify. However, that isn’t the point of electronics! We want to explore and use our amplifier to amplify unknown signals! We want to put it to use!