My sound detector - Page 1
Forum section: electronics / beginners

author: techninja80
author_rank: Regular Contributor
timestamp: September 29, 2024, 02:58:02 pm
content: So I am self learner, so this circuit is just really for me to learn. I am pretending to get an audio signal, I want to have digital light to show audio is detected, and I want to amp the signal to 12V. I know there are circuits that I can just look up an copy, but I wanted to test my understanding so this is what I came up with with my current knowledge base. Now I know its wrong, I can't seem to figure out when I try to boost it to 12V I get a poor signal. I tried to use boost, and boost1 as two methods to solve the problem. I provided the results for boost1. Please let me know what I did wrong. Forgot to mention all the opamps are lm358

author: Andy Chee
author_rank: Super Contributor
timestamp: September 29, 2024, 05:29:37 pm
content: According to your waveform, the blue trace Vboost1 is reaching 12V no problem.What was your intended waveform? You can use paintbrush to sketch the waveform over the top of your image.

author: techninja80
author_rank: Regular Contributor
timestamp: September 30, 2024, 01:11:24 am
content: Thanks I want the waveform to be an amplified version of looksig1

author: PGPG
author_rank: Frequent Contributor
timestamp: September 30, 2024, 02:11:38 pm
content: Quote from: techninja80 on September 30, 2024, 01:11:24 amFirst.Transistor in common emitter configuration reverses the phase so you can have input signal amplified for some negative factor.Second.In your circuit whenever looksig1 goes below 0.7V the Q20 is switched off so the voltage at its collector is set by X7 resistor to be 12V.Third.To get a controlled gain of transistor working in common emitter configuration you have to use negative feedback.There are two possibilities:1.Adding resistor in emitter. The expected gain will be -Rc/Re (Rc - resistor in collector, Re - resistor in emitter).2.Driving base from source via Rb and adding resistor between collector and base (Rcb). The intended gain is -Rcb/Rb.Just do some simulations only of this single transistor amplifier.

author: techninja80
author_rank: Regular Contributor
timestamp: September 30, 2024, 11:02:51 pm
content: Thanks @PGPG you have given me some keywords for fundamentals on transistors I can dig into. Hopefully it is fruitful. I will report back when I find where this brick road takes me.

author: ledtester
author_rank: Super Contributor
timestamp: October 01, 2024, 12:09:48 am
content: I would recommend Malvino's "Transistor Circuit Approximations" book to be good for self-study.

author: PGPG
author_rank: Frequent Contributor
timestamp: October 01, 2024, 01:05:23 pm
content: Quote from: techninja80 on September 30, 2024, 11:02:51 pmWhen you will understand how transistor works you can check your knowledge by trying to analyse how my oscilloscope Y amplifier works (being a student to have oscilloscope I had to design and make it):https://archive.org/details/Re0184OCR/Re_04_84_OCR/page/n7/mode/2upFortunately schematics are international languageAt left is the Y pre-amplifier and right top is final amplifier controlling the deflection plates in the oscilloscope tube.