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Logarithmic amplifier
My son wanted to design a circuit to convert microphone inputs to loudness measurements usable by an Arduino (or other ATMega processor). We discussed the idea together, coming up with a few different...
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Logarithmic amplifier again
Yesterday, in Logarithmic amplifier, I ended with the following plot: (click plot to see larger version) The cloud of points is broad enough to be consistent with slightly different parameter values. I...
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Still more on log amplifiers
Yesterday, I spent the day testing different transistors in the log amplifier, to see whether it made much difference which transistor I used. I wanted to test all 11 transistors in the iteadstudio...
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Precision rectifier
The log amplifier that I’ve spent the last several days understanding (posts a, b, c) is not the only non-linear circuit needed for a loudness detector. We also need to convert the audio input signal...
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Improved rectifier
In the Precision rectifier post, I gave the simplest circuit for making a precision rectifier: This circuit is both a log amplifier and a precision rectifier. If Vb is set to a constant voltage, then...
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Improved rectifier with Schottky diodes
In the Improved rectifier post, I gave the following circuit for an inverting rectifier and showed traces of its performance using diode-connected S9018 NPN transistors as diodes: Only one of D1 and D2...
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Virtual ground circuits
To use single-supply op amps properly, one usually needs to create a “virtual ground” or “bias voltage” between the two power-supply rails. I have used 3 different circuits for these virtual grounds:...
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Wire loop vs. twisted pair try 1
I was thinking about things we might do in the first lab day for the Applied Circuits course next quarter, now that I have 2 lab sessions a week. The first, obvious thing is to unpack the lab kits and...
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More on loudness circuits
My son got interested in a loudness circuit again, and we tried coming up with one that that would take few components. We decided on having a 3-stage system: a preamp to get voltage up, a peak (or...
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First op amp lecture
Today’s lecture was the first introduction of op amps to the students. I managed to present The basic notion of a differential amplifier: . Generic negative feedback amplifier. Generic...
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Block diagrams and audio amps
In today’s lecture, I introduced the notion of block diagrams as having two types of objects: functional blocks and connections between them. I emphasized that both parts were equally important, though...
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Audio amp lab
As I expected, no one came to lab today with their prelab homework done. There was a lot this week, as they needed to figure out the sensitivity of the microphone, decide how to bias it, figure out the...
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Low-power audio amp lab completed
Everyone finished their audio amps yesterday and got them working, and most finished on time, though one group took a bit longer than the rest, so I was in the lab for 5 hours instead of 3. They did...
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Second op amp lecture
Today’s lecture was the second one on op amps, after their audio amp lab. I had 3 topics I wanted to cover: virtual grounds, transimpedance amplifiers, and gain-bandwidth product. The gain-bandwidth...
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Phototransistor lab
Once again, no one came to lab today with their prelab homework done. There was a lot to do again this week, as they needed to figure out how much light was emitted by an LED, how much of that would...
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Mixed topics in lecture
Today’s lecture was a mish-mash of different topics. Pre-lab assignments not getting done. I asked the students for advice on how to get them (or next year’s class) to do the pre-lab assignments before...
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Instrumentation amp from op amps still fails
I’ve been trying to decide whether to have students build an instrumentation amp out of op amps in the circuits course. Currently the INA126P instrumentation amp chip that I have them use is a black...
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Instrumentation amp from op amps fine for EKG
As I mentioned in Instrumentation amp from op amps still fails, I’ve been trying to decide whether to have students build an instrumentation amp out of op amps in the circuits course. I decided that...
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Soldered EKG from op amps
Today I decided to solder the EKG design from Instrumentation amp from op amps fine for EKG onto one of my instrumentation amp protoboards, leaving out the instrumentation amp chip—I wanted to see how...
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Freshman design projects moderately successful
I just finished grading this year’s freshman design projects. I think that the projects were more successful this year than last year, in part because I kept the students focussed on electronics and...
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