Okay, may sound daft and there appears to be very little on this for me to research and understand.
this link explains a little on what I have found.
In theory from what I read:-
an ardunio pwm pin wires to (speaker/ microphone terminal on the gsm module), I cant see why it be a speaker though as sending signals from the gsm to another mobile phone. Not listening locally, so speaker pointless, but microphone would be incoming sound?
So a resistor is required to mimic the resistance of the speaker/ microphone and the pwm pin delivers the audio from a file.
Before I go out and get a sim card module does anyone know where i can find more info on this, resistor value and confirm if it is the speaker or microphone I need to use or if its complete and utter rubbish.
or if its complete and utter rubbish.
That link to stack exchange is true, but your understanding about what is happening is very flawed.
What you need on the output pin of the Arduino is an RC ( resistor capacitor ) filter to turn the PWM signal into an analogue one. You can then apply that signal to an Audio input of a amplifier or other input device. This is a common practice so I find it hard you can’t find any examples on the web.
I even showed another method in my book Arduino Music and Audio Projects | SpringerLink and there are lots of videos about again like mine at https://m.youtube.com/watch?v=WShVFcrFpwU
So a resistor is required to mimic the resistance of the speaker/ microphone and the pwm pin delivers the audio from a file.
No, the Arduino doesn't require a load. But you might need to add a filter to block the DC component and to make the PWM more "analog-like".
...and confirm if it is the speaker or microphone I need to use or if its complete and utter rubbish.
As I'm sure you know... A speaker converts electrical signals to sound and a microphone converts sound to electrical signals.
If you need a microphone, the easiest thing is to buy a microphone shield (so you don't have to build a preamp, etc.).
...It seems silly to convert digital audio (or a digital audio file) to analog (PWM), then back to digital... But if your GSM shield requires analog that's what you'll have to do.
Thank you for your contributions, it certainly gives me things to look at tomorrow.
spent some time searching and very little came up, but like all searches its how you look to return the information you really want.
excuse my ignorance. been at the vino tonight.
There is no point in a physical microphone as you have to have audio for a physical microphone to work, which would also mean a speaker.
however if it seems more sensible to have less hardware in this case if something can be used thats reasonable.
its finding detail that is meaningful which i often struggke with online. I mean the link I used tells you its possible???? but unable to verify it as theres no real data/ info to support it.
This is nw to me and having to learn how to do things and then decide f its what i really want or not.
we live in a world of possabilities, if only you know how to.
Thanks again and I will update if if I make any progress.
@Grumpy_Mike thanks for the link to your book and a video neither of which help me at this moment in time.
A Yes and No video playing back through a speaker means absolutely nothing wrt to this project to be honest, well other than its audio. Could do with something more constructive, I will go away and look again to find something more relevant and thanks for posting.
Your book may be very good but I couldn't be certain that purchasing it will help me whilst looking at this project.
Thanks
neither of which help me at this moment in time.
Sorry about that.
However I fail to see how it didn’t help you. Instead of sending the audio to an amplifier and speaker you simply attach it to the audio input of what ever you want.
Maybe you didn’t describe what you want to do in enough detail for us to understand.
Thanks Mike for taking the time to reply, an answer is only as good as the question, sometimes its not so easy to know how to phrase the question to get the best answer so apologies.
so lets see if I can make it a little more specific/ broken down so I can get more specific advice.
- 2 to 4 inputs (triggers)
- 2 to 4 single word messages
- GSM module mic socket to Arduino mini pro pwm terminal for the sound (RC and or cap required?)
- currently no storage other than the Arduino mini pro's built in.
so I would guess I need to know.
-
what formats of audio I can use that take up as little space if possible.
Words that may be used Armed, Disarmed, Alarm, Panic and Fire (whoops that's 5), but it would only come from 4 pins
-
what I need to try and make the paly back sound reasonable (not distorted and reasonable volume)
RC and or cap required?)
Yes. You might get away without the seriese cap if the internal circuit if the GSM has one fitted. Some times they have and sometimes they have not.
You heard the quality of my samples, that is the sort of quality you can get with just an 8 bit sample and a PWM output. You would connect the output not to an amplifier but to your microphone input jack. Having said that you might need a voltage divider to cut down the signal from the Arduino to the GSM.
Your problem is memory storage, there is not much room to store it in the program memory of a Uno or similar micros an SD card would be best. I estimate you can get about 3.5 seconds of sound without one.
The trick is recording the words using Audacity ( free app all platforms ) and then normalising the sample at 8 bits. This means scaling the sound so the loudest peak corresponds to the maximum number an 8 bit byte can hold. And then getting the Processing language to output code you can copy and paste directly into your Arduino code.
The sound format would just be raw numbers.
What you want to do can be done.
that's tight at 3.5 seconds, but I reckon less than 1 sec a word might just squeeze it in. did all 5 just under 3.5 seconds but we shall see what we can do with hat.
I get one word to stat with and see how I get on.
I can handle that level of quality.
currently the voltage supplied to the ardunio and the gsm module is 4.2V as the gsm module operates to something like 3.8 to 4.3V, I can do a divider just know how low it need to be taken.
I can do a divider just know how low it need to be taken.
Sorry but does that mean you do know how low to take it or you need to know how low. The best thing might be to have a small “preset” pot so you can adjust it foe maximum volume without distortion.
Thanks for the reply.
I know how to divide the voltage have to do that for the 13.5 volts incoming triggers.
Just need to know how low to go.
Well is is probably in the specification of the GSM module but it should be somewhere arround 10 to 100mV.
I will check the gsm specifications and the pwm output to see what I am starting with.
It is all new to me so sometimes the information staring at me I don't see.
Thanks again for your help.
Okay I am going nuts its official.....
The SIM800L spec for the Chip /the SIM800L board I cant find any spec details on at all.
have posted an update from what I can find, maybe you can point out what I should be looking at.
Thanks
cant post the sim800l chip hardware manual so heres a link instead.
and the pwm output to see what I am starting with.
You are starting with a 5V peak to peak audio signal from the Arduino Uno.
That link is not a link to a data sheet but a simple marketing sheet. You need the proper data sheet.
This is the data sheet
Datasheet_SIM800L
I will have to keep looking then
Okay extracted from the hardware manual of the sim800l
the hhardware datasheet was availavable in the original link, anyway extracted out what i think is relevant but not sure i understand what i need to d next.
I see the capacitors are recomended along with it say 2V input???
mic details.pdf (176 KB)
micdetals 2.pdf (175 KB)
mic details 0.pdf (274 KB)
Ok I can reduce the incoming max voltage to below 2V (if Ihave I read that correctly).
However I may need to look at dealing with the noise if significant by using the caps and zener diodes as show in the diagram. unless there is a solution off the shelf I can wire in?
Not sure I am ready for such a leap, I remember seeing a pcb one of my colleagues was handling many years ago, go pop when they powered up as the caps were in the wrong way round. for something so small they dont have make a bang.
Ok I can reduce the incoming max voltage to below 2V (if Ihave I read that correctly).
Yes that would be my reading of it as well.
However I may need to look at dealing with the noise if significant by using the caps and zener diodes as show in the diagram. unless there is a solution off the shelf I can wire in?
I don’t think that will be necessary, a microphone like that is a very high impedance and those capacitors are very small. Capacitors only go bang when fitted the wrong way round, these are known as polerised capacitors, there are no polerised capacitors in that microphone circuit so you can fit them any way round and they don’t go bang.
