Idahowalker
Posts: 422
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Re: Detect current on Raspberry pi

Tue Oct 30, 2018 11:59 pm

Salah wrote:
Tue Oct 30, 2018 11:24 pm
What are you referring as the intercom switch ?
The push to talk switch.
Salah wrote:
Tue Oct 30, 2018 11:24 pm

I like you idea of powering the VOX with the intercom to avoid false triggers.
I could wire the VOX directly to the speaker right ? Though I'm not sure that 3.5V would be enough to power it on.
Devices of that type are working fine with my RPi, a 3.3V device, though I have removed the mic and am just using them for amplifier and level comparator capability
Without knowing why you are deleting my postings, I will not know how...

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tlfong01
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Re: Detect current on Raspberry pi

Wed Oct 31, 2018 4:42 am

Salah wrote:
Tue Oct 30, 2018 12:24 pm
The main purpose of this project si to get notified on my smartphone when I'm away and the intercom rings.

Stupid Door Phone vs Smart Door Phone

I see. So what you need is not an ordinary door phone, but a smart door phone.

You might consider Blynk. And if your phone is too far away from the Rpi, you might need an external antenna.


Appendices - Blynk, Door Phone, External Antenna

Blynk: How to install a private local server on Raspberry Pi 3
https://diyprojects.io/blynk-how-to-ins ... 9kszpMzaUk

Control Home Appliances From Your Smarthphone With Blynk App and Raspberry Pi
https://www.instructables.com/id/Intern ... Blynk-App/

Blynk on Raspberry Pi - Digital Output
https://roboindia.com/tutorials/blynk-r ... italoutput

DHT11 and NodeMCU with Blynk
https://www.hackster.io/Manoranjan2050/ ... ynk-10e6b1

IoT : How to use Blynk App with Raspberry Pi?
https://www.youtube.com/watch?v=Cb3VK0Yl7zY

Make your own IOT apps with Blynk. NodeMCU (ESP8266) Tutorial
https://www.youtube.com/watch?v=RLKuIHaraKs

Raspberry Pi - Blynk
https://www.youtube.com/watch?v=O6q7soSepeU

ESP8266 Range Test with and without External Antenna
https://www.youtube.com/watch?v=KYLN9qH0C84

Door phone - Wikipedia
https://en.wikipedia.org/wiki/Door_phone

Wemos D1 Mini Pro external antenna ESP8266 WIFI IoT - RpiTV
https://www.youtube.com/watch?v=3lHoG1mu7hY

Wireless Remote Sensing with Wemos D1 mini, Arduino IDE, Raspberry Pi and lighttpd web server - Raspi.tv 2017jan26
https://raspi.tv/2017/wireless-remote-s ... web-server

CM3 Home AN-WIFI-01 - WiFi pcb external antenna
http://terzo.acmesystems.it/download/da ... IFI-01.pdf

CM3 Home AN-WIFI-02 - WiFi external antenna with SMA cable
http://terzo.acmesystems.it/download/da ... IFI-02.pdf
http://terzo.acmesystems.it/download/da ... -CABLE.pdf
Attachments
wemos_d1_mini_pro_ext_antenna_2018oct3103.jpg
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Last edited by tlfong01 on Thu Nov 01, 2018 2:54 pm, edited 2 times in total.
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Salah
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Re: Detect current on Raspberry pi

Wed Oct 31, 2018 12:39 pm

tlfong01 wrote:
Wed Oct 31, 2018 4:42 am

You might consider Blynk. And if your phone is too far away from the Rpi, you might need an external antenna.
I use Domoticz to control pretty much everything in my home and it's working fine so I think I'll stick to Domoticz for now and maybe try out Blynk later on, it seems pretty much similar to me.

By the way, I created the separate thread I was talking about:
viewtopic.php?f=91&t=225905

Thanks ;)

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tlfong01
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Location: Hong Kong

Re: Detect current on Raspberry pi

Wed Oct 31, 2018 2:22 pm

Salah wrote:
Wed Oct 31, 2018 12:39 pm
I use Domoticz to control pretty much everything in my home and it's working fine so I think I'll stick to Domoticz for now and maybe try out Blynk later on, it seems pretty much similar to me.

By the way, I created the separate thread I was talking about:
viewtopic.php?f=91&t=225905

Ah, Domoticz is a very powerful guy, Blynk is just a baby.

Your separate thread seems talking about the positive audio feedback thing. You need a special circuit to eliminate the feedback.

Audio feedback - Wikipedia
https://en.wikipedia.org/wiki/Audio_feedback

Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a power amplified loudspeaker).

In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again.

For small PA systems the sound is readily recognized as a loud squeal or screech.


Full-duplex Intercom without Larsen Effect (audio feedback)
https://www.eeweb.com/extreme-circuits/ ... x-intercom

As both microphones and loudspeakers are always in operation, a special circuit is used to avoid that the loudspeaker output can be picked-up by the microphone enclosed in the same box, causing a very undesirable and loud "howl", i.e. the well known "Larsen effect".

The unusual feature of this design is the microphone amplifier Q1: its 180° phase-shifted audio output taken at the Collector and its in-phase output taken at the Emitter are mixed by the C3, C4, R7 and R8 network and R7 is trimmed until the two incoming signals almost cancel out. In this way, the loudspeaker will reproduce a very faint copy of the signals picked-up by the microphone.
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Salah
Posts: 25
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Re: Detect current on Raspberry pi

Wed Oct 31, 2018 3:37 pm

tlfong01 wrote:
Wed Oct 31, 2018 2:22 pm

Ah, Domoticz is a very powerful guy, Blynk is just a baby.

Your separate thread seems talking about the positive audio feedback thing. You need a special circuit to eliminate the feedback.
Interesting, it sounds like it might be it but then I don't understand why this Larsen effect didn't occur at all without the Pi.

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Mortimer
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Re: Detect current on Raspberry pi

Wed Oct 31, 2018 9:53 pm

Salah wrote:
Wed Oct 31, 2018 3:37 pm
Interesting, it sounds like it might be it but then I don't understand why this Larsen effect didn't occur at all without the Pi.
Because the audio circuitry of the handset by its self was carefully designed so that the microphone audio and speaker audio were 180 degrees out of phase and at an amplitude that any locally fed noise would cancel itself out. The audio circuitry of the USB audio dongle was likely in-phase and therefore re-inforced the local feedback loop resulting in a very high pitched squeal that got amplified at both ends of the intercom link.

Salah
Posts: 25
Joined: Mon Jul 09, 2012 12:47 pm

Re: Detect current on Raspberry pi

Wed Oct 31, 2018 10:38 pm

Mortimer wrote:
Wed Oct 31, 2018 9:53 pm
Because the audio circuitry of the handset by its self was carefully designed so that the microphone audio and speaker audio were 180 degrees out of phase and at an amplitude that any locally fed noise would cancel itself out. The audio circuitry of the USB audio dongle was likely in-phase and therefore re-inforced the local feedback loop resulting in a very high pitched squeal that got amplified at both ends of the intercom link.
I'm not sure I fully understand how the USB audio is causing this feedback loop.

With your explanation I understand that there is an electronic design into the intercom which already cancels this loop.

But since I'm listening / pushing audio at the handset level with the Pi, the same "treatment" should be applied right ?
The way I see it is like the Pi is listening / speaking to the handset and it works for a regular human, so why not for the Pi ? :D

The USB audio dongle has 2 separate jacks, one for input and one for output, so the audio signals should be separated.

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Mortimer
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Re: Detect current on Raspberry pi

Wed Oct 31, 2018 11:04 pm

Salah wrote:
Wed Oct 31, 2018 10:38 pm
Mortimer wrote:
Wed Oct 31, 2018 9:53 pm
Because the audio circuitry of the handset by its self was carefully designed so that the microphone audio and speaker audio were 180 degrees out of phase and at an amplitude that any locally fed noise would cancel itself out. The audio circuitry of the USB audio dongle was likely in-phase and therefore re-inforced the local feedback loop resulting in a very high pitched squeal that got amplified at both ends of the intercom link.
I'm not sure I fully understand how the USB audio is causing this feedback loop.

With your explanation I understand that there is an electronic design into the intercom which already cancels this loop.

But since I'm listening / pushing audio at the handset level with the Pi, the same "treatment" should be applied right ?
The way I see it is like the Pi is listening / speaking to the handset and it works for a regular human, so why not for the Pi ? :D

The USB audio dongle has 2 separate jacks, one for input and one for output, so the audio signals should be separated.
Try swapping the polarity of one of the devices, either the speaker or the microphone and see if that cures the problem.

Salah
Posts: 25
Joined: Mon Jul 09, 2012 12:47 pm

Re: Detect current on Raspberry pi

Thu Nov 01, 2018 12:17 am

Mortimer wrote:
Wed Oct 31, 2018 11:04 pm
Try swapping the polarity of one of the devices, either the speaker or the microphone and see if that cures the problem.
I've just swapped the polarity from the microphone by swapping the wires that I had soldered to the jack connector:
I can hear the communication on the phone but I can't hear anything at the entrance intercom.

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Mortimer
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Re: Detect current on Raspberry pi

Thu Nov 01, 2018 11:32 am

Hmm! the microphone might be polarised (is it an electret mic?). Try swapping the speaker wires instead.

Salah
Posts: 25
Joined: Mon Jul 09, 2012 12:47 pm

Re: Detect current on Raspberry pi

Thu Nov 01, 2018 6:58 pm

Mortimer wrote:
Thu Nov 01, 2018 11:32 am
Hmm! the microphone might be polarised (is it an electret mic?). Try swapping the speaker wires instead.
I googled electret mic and mine looks like this: https://www.jayconsystems.com/media/cat ... 0001_7.jpg
So I think it is an electret mic indeed.

I swapped back the mic polarity and swap the speaker polarity, now it's the reverse result:
I can't hear anything on the phone, but I can hear the communication at the entrance intercom.


I attached a basic "scheme" of the wiring to make things clearer.
Attachments
schema.jpg
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Mortimer
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Re: Detect current on Raspberry pi

Thu Nov 01, 2018 8:41 pm

Then it doesn't look like you can re-create the phase-cancellation of the device in its native form using the USB sound dongle and RPi.

You might be able to find some software that will do the feedback cancellation for you, I don't know.

Salah
Posts: 25
Joined: Mon Jul 09, 2012 12:47 pm

Re: Detect current on Raspberry pi

Fri Nov 02, 2018 10:41 am

I really don't understand how the Pi would provoke the audio loop but the intercom handset on its own wouldn't.

I ordered an audio amplifier and I will connect a speaker to the Pi audio output.
I think this would work but this is a workaround :(

drgeoff
Posts: 8864
Joined: Wed Jan 25, 2012 6:39 pm

Re: Detect current on Raspberry pi

Fri Nov 02, 2018 12:18 pm

About the nonsense in posts above about phase. You'll get audio path positive feedback irrespective of fiddling with phase of speaker or microphone. Howl frequency will change but will still be there. The handset doesn't avoid this by getting the phase correct. The original design keeps the volume from the speaker, the sensitivity of the microphone, the loss in the acoustic path between those two and the electronic gain such that the total path loss around the loop is greater than unity at all frequencies.

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Mortimer
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Re: Detect current on Raspberry pi

Fri Nov 02, 2018 12:25 pm

So you think just turning the mic gain down will be enough?

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tlfong01
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Location: Hong Kong

Re: Detect current on Raspberry pi

Fri Nov 02, 2018 2:15 pm

Salah wrote:
Fri Nov 02, 2018 10:41 am
I ordered an audio amplifier and I will connect a speaker to the Pi audio output.

Ah, so you are a DIYer.

I would suggest to also add a camera and touch screen to Rpi, to make something like below.

Doorbot - Use Your Smartphone As A Door Entry System
https://www.youtube.com/watch?v=9uiyUkghgE8

Amazon Doorbot Wi-Fi Enabled Smart Doorbell - USD170
https://www.amazon.com/Doorbot-Doorbell ... 008000][i]

AliExpress Smart Wireless WiFi Security DoorBell Visual Recording Consumption Remote Home Monitoring Night Vision Smart Video Door Phone US$34[/url][/i][/color]
https://www.aliexpress.com/item/Smart-W ... d5f46f03-0

This wifi doorbell can connect home WiFi and achieve a two way intercom between the doorbell and cell phone. When a visitor presses the doorbell sound is activated and the camera will start sending real time images and call to the cell phone. The user will receive the call and can check who the visitor is, can intercom with the visitor and remotely unlock the door.
Last edited by tlfong01 on Sat Nov 03, 2018 7:44 am, edited 1 time in total.
I am an electronics and smart home hobbyist.

Salah
Posts: 25
Joined: Mon Jul 09, 2012 12:47 pm

Re: Detect current on Raspberry pi

Fri Nov 02, 2018 11:27 pm

pcmanbob wrote:
Thu Oct 18, 2018 2:17 pm
Yes you could use that opto isolator , you need a resistor to limit the current flowing through the LED, because if you just connected 3.6V to the LED you would burn it out.

so using the opto isolator you selected you now need a 330Ω resistor. You will also need a diode connected in reverse with the LED because you will be applying a signal to the speaker that could cycle positive and negative.

I have also shown how to connect the output of the opto isolator to the pi gpio so that it produces a true on speaker activation, but this will probably be a pulsing output so you will need to take that in to account when programming.

Image

https://github.com/raspberrypilearning/ ... up_down.md
I received the components today and gave it a try, it works perfectly well.
Thank you ;)

pcmanbob
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Location: Mansfield UK

Re: Detect current on Raspberry pi

Sat Nov 03, 2018 12:38 am

Glad it works for you, some times following the KISS principle works.

Keep It Simple Stupid

Often applied in the world of electrical and mechanical engineering.
Remember we want information.......................no information no help
The use of crystal balls & mind reading is not supported

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tlfong01
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Location: Hong Kong

Re: Detect current on Raspberry pi

Sun Nov 04, 2018 3:57 am

tlfong01 wrote:
Mon Oct 22, 2018 1:34 pm
I have been using the same USB sound stick for both Rpi 3 and Windows 10 and so far so good. I once played with the SnowBoy thing and found no problems.
Snowboy, a Customizable Hotword Detection Engine
http://docs.kitt.ai/snowboy/

Troubleshooting Rpi Larsen Effect Problem

I often had problems using Rpi audio hardware and software. One of my usual troubleshooting tricks is to try out the Rpi3 problematic hardware / software configuration in Windows 10.

Sound Audio Playback Echo on Windows 10 OT- unwanted sound echo

... I want to disable the strange echo/surround sound effect that I have, no matter what playback I disable or configure or whatever setting I change related to sound, this echo doesn't go away. I'm starting to get frustrated over this.

https://answers.microsoft.com/en-us/win ... b7dfbef8aa

Sound problems can be caused by cables that aren't connected properly, damaged drivers, incompatible drivers, sound settings, missing updates, and problems with your sound card.

1. uninstall the sound card drivers
2. restart the computer.
3. install the latest drivers and check if that resolves the issue.

-- answers.microsoft.com
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tlfong01
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Location: Hong Kong

Re: Detect current on Raspberry pi

Sun Nov 04, 2018 8:40 am

Salah wrote:
Fri Nov 02, 2018 10:41 am
I really don't understand how the Pi would provoke the audio loop but the intercom handset on its own wouldn't.

Your door phone might have a circuit similar to below. You need to have a schematic before doing circuit analysis.

Update 2018nov05hkt0835
And to analyse the three transistor intercom circuit, you need to have some basic understanding of bipolar transistor circuits.


Introduction to Bipolar Transistor and Circuits - electronics-tutorials.ws
https://www.electronics-tutorials.ws/tr ... ran_1.html
https://www.electronics-tutorials.ws/tr ... ran_2.html
https://www.electronics-tutorials.ws/tr ... ran_3.html
https://www.electronics-tutorials.ws/tr ... ran_4.html
/ to continue, ...

Three transistor intercom Circuit
http://www.circuitstoday.com/transistor ... om-circuit
Attachments
three_transistor_intercom_cct_2018nov0401.jpg
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tlfong01
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Re: Detect current on Raspberry pi

Thu Nov 08, 2018 9:26 am

tlfong01 wrote:
Sun Nov 04, 2018 8:40 am
Salah wrote:
Fri Nov 02, 2018 10:41 am
I really don't understand how the Pi would provoke the audio loop but the intercom handset on its own wouldn't.
Your door phone might have a circuit similar to below. You need to have a schematic before doing circuit analysis.

The intercom feedback loop

Let me make simple things more complicated. Actually the feedback loop is not simple audio only, but at least following complicated:

audio > mechanical > magnetic > electrical > electronic > electrical >

magnetic > mechanical > audio, ...


It is too confusing for my little head, how come electronic has only one seat, all other guys occupy two seats? Did I carelessly miss any link? And is piezo mechanical?

/ to continue, ...
Attachments
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tlfong01
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Re: Detect current on Raspberry pi

Sun Nov 11, 2018 6:38 am

tlfong01 wrote:
Sun Nov 04, 2018 8:40 am
Salah wrote:
Fri Nov 02, 2018 10:41 am
I really don't understand how the Pi would provoke the audio loop but the intercom handset on its own wouldn't.
Three transistor intercom Circuit
http://www.circuitstoday.com/transistor ... om-circuit

One transistor audio amplifier

To keep things simple, we can abstract the three transistor amplifier to one transistor. The basic circuit analysis is more or less the same.

Transistor amplifier - CircuitsToday 2018jul26
http://www.circuitstoday.com/transistor-amplifier

.. Use Zobel network to prevent Larsen effect,

Zobel network - Wikipedia
https://en.wikipedia.org/wiki/Zobel_network

... Picture of BBC engineers playing with the Zobel thing 1959
...
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tlfong01
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Re: Detect current on Raspberry pi

Sun Nov 18, 2018 12:46 pm

tlfong01 wrote:
Sun Nov 11, 2018 6:38 am
tlfong01 wrote:
Sun Nov 04, 2018 8:40 am
Salah wrote:
Fri Nov 02, 2018 10:41 am
I really don't understand how the Pi would provoke the audio loop but the intercom handset on its own wouldn't.
Three transistor intercom Circuit
http://www.circuitstoday.com/transistor ... om-circuit
One transistor audio amplifier
To keep things simple, we can abstract the three transistor amplifier to one transistor. The basic circuit analysis is more or less the same.

AC Signal Detector Causing Positive Feed Back

Now let us see why the original intercom circuit is stable, but the added in voice/ring detector might cause a positive feedback.

First of all, the input to the audio amp is an AC signal, and output also AC. So the added voice detector is actually an AC signal detector, as illustrated in the simplified block diagram below.

We need to understand some basics of the audio amp, before trying to avoid positive feedback.

Transistor amplifier - CircuitsToday 2018jul26
http://www.circuitstoday.com/transistor-amplifier

Bandwidth
The range of frequency that an amplifier can amplify properly is called the bandwidth of that particular amplifier.

The band width of a good audio amplifier must be from 20 Hz to 20 KHz because that is the frequency range that is audible to the human ear.


Stability
Stability is the capacity of an amplifier to resist oscillations. These oscillations may be high amplitude ones masking the useful signal or very low amplitude, high frequency oscillations in the spectrum.

Usually stability problems occur during high frequency operations, close to 20KHz in case of audio amplifiers.

Adding a Zobel network at the output, providing negative feedback etc improves the stability.


Common emitter RC coupled amplifier
The job of Ce is to bypass this alternating component of the emitter current. If Ce is not there , the entire emitter current will flow through Re and that causes a large voltage drop across it. This voltage drop gets added to the Vbe of the transistor and the bias settings will be altered. It reality, it is just like giving a heavy negative feedback and so it drastically reduces the gain.

/ to continue, ...
...
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tlfong01
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Re: Detect current on Raspberry pi

Sun Nov 25, 2018 12:28 pm

Mortimer wrote:
Thu Nov 01, 2018 8:41 pm
1. Then it doesn't look like you can re-create the phase-cancellation of the device in its native form using the USB sound dongle and RPi.
2. You might be able to find some software that will do the feedback cancellation for you, I don't know.

Selecting Game Mode of USB Sound Card should increase negative feedback

1. Modern USB sound cards such as those of Ugreen with Cmedia CM6533 chip set are digitally programmable. And their sound cards can manually select play mode. For example, the Ugreen USB Multimode External Sound Card has the following modes:

1. Raw mode - hifi
2. Film mode - surround sound
3. Music mode - low and high freuency compensated
4. Game mode - low frequency boost, high frequency attenuated

Since oscillation usually occurs at frequencies at the 20kHz end, selecting game mode to decrease gain at that end might give negative feedback.

(Single Transistor Audio Amp) - tlfong01 2018-Nov-18 viewtopic.php?f=91&t=224976&start=25#p1393479
Stability is the capacity of an amplifier to resist oscillations.
Usually stability problems occur during high frequency operations, close to 20KHz in case of audio amplifiers.
providing negative feedback etc improves the stability.

Appendices - USB Sound Card Update

Ugreen USB 2.0 Multimode External Sound Card US$12
https://www.aliexpress.com/store/produc ... 3f51ALwPZZ

Raw mode - hifi
Film mode - surround sound
Music mode - low and high freuency compensated
Game mode - low frequency boost


Cmedia CM6533 chip set (with 5 band equalizer and AGC)
https://www.cmedia.com.tw/products/USB2 ... ED/CM6533N

Built-in 8051, 256K Byte flash, 32k RAM, GPIO pins, I2C/SPI/UART
DAC/ADC 8 ~ 96kHz sampling rate, 16/24 bits resolution
Equalizer to compensate microphone and headphone frequency response


Top 10 Best Usb Sound Card Black Friday Deals 2018 - November 23, 2018 by Ami Way
https://technostalls.com/best-usb-sound ... day-deals/

consulted 50 experts and surveyed 7,000 users

Top 10 best Usb Sound Card 2018

1) USB Sound Card Adapter BENGOO External Audio Adapter

2) Sabrent USB External Stereo Sound Adapter

3) UGREEN USB Audio Adapter External Stereo Sound Card

It protects against electromagnetic interference and enjoy the stable and best sound quality; a second sound source for simultaneous operation of loudspeakers and headphones.

4) Sound Blaster Play! 3

5) UGREEN USB Sound Card External Converter

6) Sabrent Aluminum USB External Stereo Sound Adapter

7) StarTech.com 7.1 with SPDIF Digital Audio

8) Plugable USB Audio Adapter

9) HyperX Cloud Virtual 7.1 Surround Sound USB Card

10) Creative Sound Blaster Omni Surround 5.1 with headphone amp and Integrated beam forming microphone


Rpi GPIO direct control audio Power Amp PAM8610 References

AliExpress PAM8610 7~15V Small Power Mini Class D Digital Audio Power Amplifier Board - US$7.20
https://www.aliexpress.com/item/DIY-PAM ... 810d9ecbfe

Pop Noise Suppression, 32 Step DC Volume Control,
Low EMI, standby, fade, mute mode,
Differential input eliminates noises that appear on the two input lines of the channel,
Direct Output to speaker


PAM8610 10W Stero Class-D Audio Power Amplifier DC Volume Control
https://www.diodes.com/assets/Datasheets/PAM8610.pdf

Rpi Zero Audio Bonnet, UDA1334A based by Adafruit, USD10 - Julian Horsey 2018nov29
https://www.geeky-gadgets.com/raspberry ... 9-11-2018/

NXP UDA1334A Low power audio DAC
https://www.nxp.com/docs/en/data-sheet/UDA1334ATS.pdf
With de-emphasis (high frequency boost) on/off control.

...
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tlfong01
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Re: Detect current on Raspberry pi

Sat Dec 08, 2018 4:58 am

tlfong01 wrote:
Sun Nov 25, 2018 12:28 pm

/ to continue, ...

AliExpress MAX9812L electret microphones Microphone sensor amplifier module - US$2.30
https://www.aliexpress.com/item/MAX9812 ... 44767df5-4

Amazon Radio Shack 12VDC Mini Buzzer by Radio Shack - Price: USD$29.99
https://www.amazon.com/RADIO-SHACK-12VD ... B01BH0I5SU
Arrives before Christmas.

How Doorbells [Electromagnetic Buzzers] Work - Tom Harris
https://home.howstuffworks.com/home-imp ... rbell2.htm

MAX9812H Datasheet
https://datasheets.maximintegrated.com/ ... X9813L.pdf

Buzzer - Wikipedia
https://en.wikipedia.org/wiki/Buzzer
https://en.wikipedia.org/wiki/Joseph_Henry
...
Attachments
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Last edited by tlfong01 on Sun Dec 09, 2018 5:16 am, edited 1 time in total.
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