Op amp on the Moon: Reverse-engineering a hybrid op amp module

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Ken Shirriff has written an article on reverse engineering a hybrid op amp module:

I recently obtained a mysterious electronic component in a metal can, flatter and slightly larger than a typical integrated circuit.1 After opening it up and reverse engineering the circuit, I determined that this was an op amp built for NASA in the 1960s using hybrid technology. It turns out that the development of this component ties connected several important people in the history of semiconductors, and one of these op amps is on the Moon.

See the full post on his blog.

App note: EMI-hardened operational amplifiers reduce inaccuracies

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EMI reduction built-in on op amps, app note from Texas Instruments. Link here (PDF)

Operational amplifiers (op amps) with electromagnetic interference (EMI) filters can reduce significant errors. These types of errors are not always obvious to the system designers. They often impact the signal chain, in particular the analog-to-digital converter in the form of a loss of digital counts.

App note: How to properly configure unused operational amplifiers

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Good read app note from Texas Instruments about configuring unused op amps on multi amp chips. Link here (PDF)

Multi-channel operational amplifiers (op amps) are often implemented in circuits that do not require the use of all channels. Undesired behavior in an unused amplifier channel can negatively impact system performance, as well as the performance of the channels in use. To avoid degradation of both the op amp and system performance, the unused op amp channels must be configured properly.

App note: A microwatt charge pump boosts 1 V to 1.8 V at 90% efficiency, providing “Always On” standby power for microcontrollers

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Interesting app note from Silicon Labs on high efficiency charge pump utilizing their nanopower TS1001 op amp. Link here (PDF)

Boosting the output voltage of common alkaline button-cells to at least 1.8 V needed by microcontrollers provides an “always on” standby power source sufficient for low-power oscillator interrupt/sleep state operation. Two ultralow power op amps are used in a charge pump configuration to double an input voltage, creating an output voltage of approximately 2x the input voltage. Output currents up to 100 µA are available at 90% efficiency; even load currents as low as 10 µA achieve 80% efficiency, beating commercially available charge pump ICs and inductorbased boost regulators.

A Buck-Boost Converter from the Ground Up

DC to DC conversion has come a long way. What was once took an electromechanical vibrator and transformer has been reduced to a PC board the size of a largish postage stamp that can be had for a couple of bucks on eBay. So why roll your own buck-boost converter for the ground up? Maybe because sometimes the best way to learn is by doing.

When it comes to clear and succinct explanations, [GreatScott!] has you covered. We recently reported on one of the videos from his Electronic Basics series, but the video below covers the slightly more advanced topic of DC-DC conversion in depth. [GreatScott!] describes how buck converters and boost converters work as separate entities, and how they can be integrated into a non-inverting buck-boost converter. He further simplifies that circuit into an inverting buck-boost, and sets about explaining the limitations of the circuit. With the addition of an op amp to provide feedback to control the duty cycle of the ATtiny85, the buck-boost overcomes its limitations and keeps a solid set point regardless of load or supply voltage.

If you’re looking to get into the theory of DC-DC conversion by putting it into practice, this is a great project to get you started. It’s also a good review for the old hands, as are most of [GreatScott!]’s videos. They’re worth checking out.

 


Filed under: Arduino Hacks, classic hacks

Simple Hearing Amplifier

Hearing aids are probably more high-tech than you think. They are tiny. They have to go through a lot of trouble to prevent feedback. They need a long battery life. The good ones match their amplification to the inverse of your hearing loss (amplifying only the bands where you don’t hear as well).

[NotionSunday] put together a hearing amplifier project that probably doesn’t hit many of those design criteria. However, thanks to a 3D printed case, it looks pretty good. The device uses a dual opamp to boost the output from two microphones and feeds it to a conventional headphone.

The device is wired point to point, and is, perhaps, pocket-sized. The opamp circuit is simple. We might have considered an LM386 or some other integrated audio amplifier block to get better performance without blowing up the parts count.

Technically, devices like this are not really hearing aids, they are “personal sound amplifiers” and the FDA warns people not to substitute them for hearing aids. If you want a proper hearing aid, you might check this out, but  you are going to need big ears since it has an Arduino inside.


Filed under: 3d Printer hacks, misc hacks

Faux-AI Clapper Almost Seems to be Listening

When a job can be handled with a microcontroller, [devttys0] likes to buck the trend and build a circuit that requires no coding. Such was the case with this “Clapper”-inspired faux-AI light controller, which ends up being a great lesson in analog design.

The goal was to create a poor man’s JARVIS – something to turn the workshop lights on with a free-form vocal command. Or, at least to make it look that way. This is an all-analog circuit with a couple of op amps and a pair of comparators, so it can’t actually process what’s being said. “Aziz! Light!” will work just as well as any other phrase since the circuit triggers on the amplitude and duration of the spoken command. The AI-lite effect comes from the clever use of the comparators, RC networks to control delays, and what amounts to an AND gate built of discrete MOSFETs. The end result is a circuit that waits until you finish talking to trigger the lights, making it seems like it’s actually analyzing what you say.

We always enjoy [devttys0]’s videos because they’re great lessons in circuit design. From block diagram to finished prototype, everything is presented in logical steps, and there’s always something to learn. His analog circuits that demonstrate math concepts was a real eye-opener for us. And if you want some background on the height of 1980s AI tech that inspired this build, check out the guts of the original “Clapper”.


Filed under: home hacks, misc hacks

DIY ECG with 1 op-amp

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A DIY ECG made from single op-amp (LM741) and 5 resistors by Scott Harden:

I made surprisingly good ECG from a single op-amp and 5 resistors! An ECG (electrocardiograph, sometimes called EKG) is a graph of the electrical potential your heart produces as it beats. Seven years ago I posted DIY ECG Machine on the Cheap which showed a discernible ECG I obtained using an op-amp, two resistors, and a capacitor outputting to a PC sound card’s microphone input. It didn’t work well, but the fact that it worked at all was impressive! It has been one of the most popular posts of my website ever since, and I get 1-2 emails a month from people trying to recreate these results (some of them are during the last week of a college design course and sound pretty desperate). Sometimes people get good results with that old circuit, but more often than not the output isn’t what people expected. I decided to revisit this project (with more patience and experience under my belt) and see if I could improve it. My goal was not to create the highest quality ECG machine I could, but rather to create the simplest one I could with emphasis on predictable and reproducible results. The finished project is a blend of improved hardware and custom open-source software, and an impressively good ECG considering the circuit is so simple and runs on a breadboard! Furthermore, the schematics and custom software are all open-sourced on my github!

Project info at Scott Harden’s blog.