Using the Labrador to examine the amplifier’s AC signal response.

Compared to the DC Sweep experiment, AC signal response is far easier to do.

Before we dive into how to perform the analysis, let’s discuss why we made the decision to add a bias resistor. Let’s start with the same amplifier design, however, we’ll use two supplies:

From the time domain graph, you can see a few things:

Using the Labrador and a DMM, perform a DC sweep of an inverting amplifier. From our previous lab post we saw the simulation values for a DC Sweep. In this lab, we’ll use the Labrador along with a DMM to determine if our measured values match those of the simulation.

Build the Circuit on a Breadboard#

1. Using this circuit, implement on a breadboard so it is similar to the image below.

   

2. Parts List:
   • LM358 Operational Amplifier
   • Frequency Generator (Espotek Labrador or ADALM1000)
   • 9V power supply
   • 2k ohm resistor (or 10k potentiometer)
   • 5k ohm resistor (or 10k potentiometer)

Notes:#

1. Vo is pin 1 on the chip
2. Vn is pin 2 on the chip
3. Vp is pin 3 on the chip
4. Make sure you attach 9V to pin 8 and Ground to pin 4

   

Using a Potentiometer as a variable voltage source#

Notice the potentiometer on the right on the breadboard. There are three terminals:

How to resolve a possible software bug on the Labrador.

Update August 1, 2021#

I’ve noticed that the “Paused” check box appears to “delete the buffer and force a reload”. For example, I might see some clipping on a sine wave and if I check/uncheck Paused, the wave will appear accurately. This would help explain why “checking and unchecking Paused” can fix a multitude of sins. Therefore my new advice is, if your results aren’t what you expect, do the following:

How to install the software then perform a hardware calibration.

The video assumes you have installed the Labrador application and wish to better understand how to do a calibration. It also shows how to solve a multimeter software bug.

Overall Process:#

1. For all of the OS versions; Windows, Linux, macOS, go to the github releases page for the Espotek Labrador and download the appropriate image.
2. Each OS has its own set of installation instructions, and are very similar to other installations for the same type of software.
3. Once installed, calibrate and perform the simple test in this presentation to confirm its operating properly

Comments on Installations#

• Windows
  • Typical install with multiple click-throughs
  • Make sure you note where you installed it
  • Double-click the application to start the application
• Linux
  • Use Appimage version to keep installation simple
  • Two right-click operations to start the application
• macOS
  • Drag download to Applications folder
  • Right-click to Open
  • Click on Open to start the application

Hints for next steps#

1. Calibrate the Oscilloscope#

To make it easier to connect both wires to USB shield:

A brief introduction of the Espotek Labrador.

Description#

This entry begins a series of entries discussing the Espotek Labrador. It is a fantastic small device that enables one to analyze electronic circuits.

https://espotek.com/labrador/

From that page is this description:

Labrador is an all-in-one tool for electronics students, makers and hobbyists. Just plug your Labrador board into a PC (Windows/Mac/Linux), Raspberry Pi or Android device via a MicroUSB cable, load up the software and you instantly have the following engineering tools at your disposal:

A short course which introduces the Espotek Labrador and how to use it in analyzing circuits.

Entries#

1. Introduction
2. Installation and Calibration
3. Software Bug
4. DC Sweep
5. AC Signal Analysis
6. Programmable Bias and Gain
7. Filters
8. Understand Your Test Equipment
9. Testing the ESP32 and MicroPython
10. Testing the RP2040 and MicroPython