search

Adrianotiger / phoneDTMF

Detect DTMF without external devices
26 stars 6 forks source link

question about volume voltage needed #2

Closed hayden-t closed 1 year ago

hayden-t commented 1 year ago

Im trying to get this working off a mobile phone, i measure the peak to peak voltage of dtmf tone app via my oscilloscope and its about 150mv, does this sound right ??

though it might have been around 1v

do you know what would be needed for the arduino before you need an op amp as mentioned in the readme ??

hayden-t commented 1 year ago

using a headphone output on my computer speaker amp im getting results just not the right key codes. at least its something i can work on

Adrianotiger commented 1 year ago

Im trying to get this working off a mobile phone, i measure the peak to peak voltage of dtmf tone app via my oscilloscope and its about 150mv, does this sound right ??

though it might have been around 1v

do you know what would be needed for the arduino before you need an op amp as mentioned in the readme ??

1V is a great value. On the analog input, you can measure (10bit) with 1024 values. 5V/1024= 5mV for unit. To filter it out, you can for example set the threshold to 0.5V or 100 units. On this library you could just amplify the signal over the software using 4 as value.

I don't know if the mobile phone use the same frequency as the landline phone.

hayden-t commented 1 year ago

its an app that does dtmf,

if arduino cant measure negative does the sine wave sound signal get cut in half ? no sound is 0v right ?

ill try measuring my amp output and keep tinkering, atleast ive got some response from the library and arduino to work with

hayden-t commented 1 year ago

ok the problem was i had my scope probe in 10x mode, but for sound i need 1x , now im getting sensible voltage. 1.5v pp at max volume, still curious about if the sound wave gets cropped down the middle horizontally

Adrianotiger commented 1 year ago

You need to set the middle of your AC signal to 2.5V. So, when you read the DC, it is between 0 and 5 V. You can see the schematic withe the 600:600 Transformer.

hayden-t commented 1 year ago

ok, i just got a bunch of those transformers to experiment with in different project, so will try that out, this makes more sense, so theres no way this will work with out raising the wave half your adc ??

Adrianotiger commented 1 year ago

I don't know. Probably it should be possible. My library is just a fork. It will sample the signal for 20ms to see what frequency is present. If you cut the wave under 0V, you have to analyze it differently.

hayden-t commented 1 year ago

i actually started with this page, but he seems to miss the need for this, even though theres some kind of adc in the schematic picture.