Op Amp Discovery - Quick and Versatile Prototyping and Experimenter Board

I was looking to clear some roadblocks to the hands-on learning of op amps: driving to a limited-hours lab, clearing a work space at home, buying expensive / bulky supplies / generators or struggling with messy, intermittent wiring on breadboards.

A bit of research and brainstorming led to the idea of the Op Amp Discovery Board - the best of both the solderless breadboard and PCB worlds. I created a small board with handy component headers, PCB interconnects, supply rails and a square wave generator where I could learn on my kitchen table, in the library or coffee shop.

In a short time, I got up and running many classic op amp circuits, rediscovering the fun and joy of learning about circuits. Along the journey, an Excel Op Amp Design Calculator was steadily created for each circuit adventure. This is an Open Source Project - make, copy or modify for your own learning goals.

Fast & Flexible Prototyping

The Op Amp Discovery Board allows students, engineers and DIYers to quickly build and experiment with a variety of op amp configurations. Why? Hands-on learning boosts understanding and intuition!

1. Easy-to-use hybrid (solderless breadboard / PCB).
2. Explore 20+ classic op amp circuits
3. Create your own circuits
4. Supply Rails & Signal Source Included on-board

Explore op amp circuits with component headers and configurable circuits.

1. Flexible - easily install Rs, Cs or jumpers across any headers.
2. Fun problem solving - How-to-build circuit on available component headers?
3. Configurable signal - DC, AC, square-wave, level trimpot

Problems Solved

I noticed standard breadboards can be frustrating:

1. Prone to opens, shorts, intermittent connections
2. Confusing, difficult to probe and debug
3. Requires expensive, bulky supplies and signal generators

Op Amp Discovery benefits:

1. PCB provides solid, versatile connections, power and signal source.
2. Layout arranged like schematic to reinforce learning.
3. Minimal cost and PCB space - an affordable & portable learn-anywhere lab.
4. Learning possible with a $10 DMM only.

You can follow Self-Directed or Guided Learning.

The Op Amp Discovery provides essential support circuitry for a stand-alone learning lab.

Overview

1. Proto Headers for easy component installation.
2. PCB interconnects for versatile circuit options.
3. Op Amp socket for DIP (or SMD on 8-pin header).

Signal Source

1. Square Wave Generator (0 to 5V)
2. Trimpot for Amplitude Adjust
3. External Input / Outputs (Optional)

Power Rails

1. Positive Rail VCC: Adjustable Regulator (5V default)
2. Negative Rail VEE: Cap Charge Inverter (-4.5V)
3. Power from 9V Battery or External Rails (optional).

Let’s jump in with the Non-Inverting Amplifier.

1. Review the circuit diagram (upper right)
2. Sketch out a possible build on the available headers / connections of Proto-Area Schematic. (left)
3. Install the resistors and wire jumpers - and the circuit’s ready to explore!

Now your turn with an Inverting Low-Pass Filter Amplifier.

1. Review the circuit diagram (right)
2. Sketch out a possible build on the available headers / connections of Proto-Area Schematic. (left)
3. Print out blank schematic (PDF) attached to this section.
4. Install the resistors and wire jumpers on the board you're ready to explore!

The overall strategy was to create a simple, rugged circuit using standard, generic components. While the schematic is fairly straightforward, here's a few notes about each section.

Positive Adjustable Supply

1. U1 regulates external 9V battery or power source to 5V
2. R1, R2 adjust output VCC = 1.25V x (R1+R2)/R1
3. D4 prevents Vin reverse bias damage.
4. D3 LED provides visual power indicator

Square-Wave Oscillator and Negative Rail

1. Square-Wave Oscillator (U3A, R3, R4) creates 0-5V, 5kHz signal.
2. Paralleled inverters (U3b-U3f) boost current drive.
3. Negative Rail developed by Capacitive Charge Pump (C4, C5, D1, D2).

Signal Source

1. Signal components C6, R5, R6 and C7 are easily changed on 4-pin headers for user flexibility.
2. RV1’s multi-pad PCB layout accommodates a wide variety of Trim Pot pin types.

Flexible Signal Options.

1. Select Signal Source (JP8-10): Square Wave (VSQR) or DC Level (VCC, VEE).
2. Choose DC Coupling (C6=short) or AC Coupling (C6=cap)
3. Scale signal between 0 and 5V (R-Divider R5, RV1 and R6).
4. Adjust signal level (RV1)
5. Apply Low-Pass Filter (C7 optional).

DC Signal Scaling

1. R-Divider
2. Minimum: VS_min = Vin∙R6/(R5+RV1+R6)
3. Maximum: VS_max= Vin∙(R6+RV1)/(R5+RV1+R6)
4. Default Signal Settings
5. C6=short, R5=3.01k, RV1=1k, R6=short, C7=open, JP9=ON.
6. RV1 adjusts VS for a 0 to 1.25V Square-Wave.

Op Amp Proto Area

1. Header Sockets (J3 - J8) to install components.
2. PCB traces interconnect header pins.
3. Bypass capacitors (C10, C11) to GND plane allow higher frequency applications.

Input Signals

1. Select VS, GND or VIN- (ext) to U1 NEG input path (JP2-4).
2. Select VS, GND or VIN+ (ext) to U1 POS input path (JP5-7).

With a goal of 20+ Op Amp circuits, the board evolved to the number of header pins and PCB interconnects needed to implement all of the configurations above. The collection includes the classic basic circuits as well as advanced applications.

For each circuit you wish to explore:

1. Solve the how-to-build-it on the Discovery Board using the Proto-Area Schematic.
2. Use the Excel Op Amp Calculator for component values and signal levels.
3. Build it and measure the signals around the circuit to deepen understanding.

Circuit Challenge: I imagine many more topologies are possible! What additional op amp circuits are possibe with the Discovery Board?

I wanted to create documentation anticipating the various learning styles and previous op amp experience.

1. Self-Directed Learning - Explore circuits entirely on your own.
2. Guided Learning - Follow the User's Guide and Example Circuits.
3. Combined Learning - borrow ideas from examples and follow-through on your own.

Users's Guide (PDF)

Includes a desciption and details about the board itself as well as how to dive in with learning.

1. Overview
2. Quick Start Guide
3. Schematic
4. Op Amp Basic Circuits
5. Op Amp Advanced Circuits
6. Proto Area Schematic
7. Op Amp Discovery Sheets
8. Parts List
9. Bonus Sections

Guided Circuit Examples (PDF)

The intention was to capture my own exploring and (re)learning of key op amp circuits. It was fun to figure out how-to-build-it using the available component headers and interconnections (more than one solution is typically possible). Also satisfying was the calculating, building and measuring voltages to strengthen my grasp of theory and intuition.

1. Four Key Steps
2. What You’ll Need
3. Guided Learning Examples
4. Non-Inverting Amplifier
5. Inverting Amplifier
6. Summing Amplifier
7. Differential Amplifier
8. Integrator
9. Differentiator
10. Wien-Bridge Oscillator
11. V-to-I Converter (LED Drive)
12. Sallen-Key Low-Pass Filter
13. RC Comparator Oscillator
14. Driving a Capacitive Load
15. BJT Regulator
16. Half-Wave Rectifier
17. I-to-V Converter (Photodiode)
18. Thermistor Preamp

While playing and tinkering with the op amp circuits, I began creating a set of design calculators for each of 20 configurations. For the Excel link, go to https://ecircuitcenter.com/op-amp-discovery/op-amp-discovery.html and scroll to bottom of the page.

1. Enter component values, input levels.
2. Calculate gains, output levels and frequencies.
3. Modify, customize for your own projects.

I imagine the Op Amp Discovery Board can provide opportunity in many areas. By engaging in hands-on learning, students can bridge the gap between theory and practical skills.

1. STEM High School
2. College / University
3. EE courses
4. Special Projects
5. DIY, Maker Learning
6. EE Continuing Education
7. Internships - Students / Recent Grads
8. Solder, build and test a board
9. Explore additional op amp topologies
10. Provide feedback to refine / expand training material

Internship Idea: Engineering for Under-Resourced Areas

What if Internship Students could build and test 2 Discovery boards, one for themselves and one for someone else in a part of the world that may not have access to lab equipment? With the Op Amp Discovery Board and a $10 DMM, a student anywhere could explore hands-on circuits beyond a description in a textbook.

What possibilities do you see for the Op Amp Discovery Board?

Here’s the default Parts List. Modify, customize and build it for your own learning goals.

PCB

1. 3 inch x 3 inch, Circuit Board, Double Sided, KiCAD files from Github.

Passives

1. C10, C11, C12: 0.1uF (All caps ceramic, ≥ +25V)
2. C3: 1nF
3. C1, C2: 1uF
4. C4, C5: 10uF
5. C6, R6: Short - wires or resistor leads.
6. C7, R4: Open
7. D1, D2, D4: Diode 1N5711
8. D3: LED Yel LTL-4253 Or any color you prefer.
9. R1, R7: 1k (All resistors 1/4W, 1% preferred)
10. R2, R5: 3.01k
11. R3: 200k
12. RV1: 1k trimpot side adjust 3352W-1-102LF
13. TP1: TestPoint 5011

Connectors, Headers

1. J1: 2-pin Terminal Block screw type
2. Optional: Solder 9V Battery Clip Leads or Supply Leads directly to pads.
3. J2: 3-pin Header TSW-103-08-T-S, Optional: for external inputs.
4. J9: 2-pin Header TSW-102-08-T-S, Optional: for external output.
5. JP2-JP10: 2-pin Header TSW-102-08-T-S
6. 3 shunts needed typically, SNT-100-BK-T
7. J11, J12, J13: 4-pin Socket Header, SSW-104-01-T-S

Active

1. U1: Op Amp LMC6081IN/NOP8, single amp, rail-to-rail output, +/-7.5V supply max, DIP.
2. Alternate: OP07CP, single amp, precision, +/-18V supply max, DIP.
3. U2: Linear Adjustable Regulator LM317LZ
4. U3: Hex Inverters Schmidt Trigger 74HC14APF

Sockets

1. U1 Socket: DIP-8 Socket 4808-3000-CP
2. U3 Socket: DIP-14 socket 4814-3000-CP

Having an oscilloscope to see the input / output waveforms is ideal. However, I explored many op amp topologies with only a $10 Digital Multi-Meter (DMM). The hands-on learning of amplifiers was still fun and engaging. This low-cost alernative is important for eager learners with limited budgets! I also calculated RC values for lower oscillator frequencies < 10 Hz and watched the pulsating LEDs to verify behavior.

Scope

1. Observing waveforms provides excellent insight into how circuits work.
2. Suggested: 2 channels with ≥ 1MHz Bandwidth.
3. Budget Scopes (hand-held or USB type) are available from $40 to $100.

DMM

1. A low-budget basic Digital Mult-Meter (DMM) available from $10 is a practical alternative!
2. Select the DC input source on the Discovery Bd and observe the op amp’s behavior with the DMM.
3. See Guided Examples (PDF) for learning with a DMM only.

The Op Amp Discovery Bd is an Open-Source project intended to make learning op amps as easy, fun, accessible and affordable as possible.

1. You can down load the documentation, schematics, KiCAD project files and Excel Design Calculator at https://github.com/rick-ecircuit
2. This project is shared under the MIT License.

Questions, comments, ideas?

1. What possibilities do you see?
2. Very interested to hear your thoughts!
3. You can also reach out at https://ecircuitcenter.com/op-amp-discovery/form/feedback1.html

While the User's Guide and Circuit Examples focus on basic topologies and operations, the Op Amp Discovery Board opens up possibilities to study and explore many real-world device behaviors.

1. Bandwidth
2. Max Slew-Rate
3. Voltage / Current Limits
4. Offset Errors
5. Control-Loop Theory
6. Stability

Encountering these behaviors can build practical EE skills whether designing or debugging actual op amp circuits.

Key topics can be also explored through the support circuitry.

1. Linear Adjustable Regulator
2. Square-Wave RC Oscillator
3. Capacitive Charge Pump (Negative Rail)

What further topics, articles, topics and tutorials can be written for specific courses, special projects or career development?