Sending voice to Nokia

Hi All,

I've been searching for info on this and can't find anything related.

I've got a project with a PIC16F913 interfaced to an ISD4004. I want to be able to send the voice data from the ISD to a Nokia cell. I've made up a cable consisting of a 2.5mm stereo plug on one end with an earth and a signal wire connected to the correct tabs (as per pinouts.ru). Looking at the AUD OUT pin of the ISD with my scope I can see there is output happening but when I connect the signal wire to that pin via a cap and earth the other wire I don't get any audio out of the phone.

To test this I am calling the cell with my landline and while the phone auto answers and the headset options are on I can't hear my audio down the line.

My circuit also has a rail - rail opamp in it and even if I take the audio on the output of that I don't get anything.

I can't work out what I'm doing wrong here - anyone able to help?

Thanks

Tony

Tony,

I'm not familiar with the ISD4004, but I've connected two different RC Systems speech boards to mobile phones. Both times I used a 1:1 audio transformer, as some of the amplifier chips don't like to have one side grounded. I got the transformers at Radio Shack.

It's also possible that the pinout you got off the internet is incorrect, but I can't help you there, I don't have any Nokia data.

Jerry.

Hi Tony,

as far as I remember from my Nokia phone, the headset connector was a 2,5mm plug with four contacts.
Have you verified this for your phone?
Also I would expect the input signal for the phone to be microphone level maybe there also is a bias voltage for microphone supply applied...

Regards,

Ingo

Thanks for the reply guys. This is a link to where I got the wiring for the 2.5mm jack - http://pinouts.ru/CellularPhones-Nok...t_pinout.shtml

I'm using a stereo plug and I'm using the base and middle landings which I think is correct. The output I'm using from the opamp should be a large enough signal for the Nokia.

I guess I'll just need to experiment some more to find the right connections.

Regards

Tony

Hi Tony,

are you using a 8210 cell phone for your project?
As the three pole plug seems to be used there only.
Do you have a common ground on the phone and your circuit?
Then you should check if MIC- is on ground potential.
Futhermore I don't think you will need a "strong" signal, as a microphone would not deliver more than 100mV (guess) signal.
Make sure not to overdrive the input.

Regards,
Ingo

Hi Ingo,

The phone I'm using is new (not sure what the model number is) and it uses a 4 pole socket but using a 3 pole plug should work 'cause when I plug it into the phone it recognises that a handsfree is in use.

I've connected the mic- to ground in my circuit and used the output direct from the ISD4004 but no good yet. The output from the ISD is quite low - I haven't measured it but I think it's only around 30-40mv. The gain from the opamp is about 10 so the output is quite a bit higher there.

Even so, I still get nothing out of the phone.

I'm going to keep experimenting - I should get it soon.

If I plug an earphone into the socket I should be able to hear if something is going into the mic should i not? That way I can save some money by not having to call the mobile to test it.

Thanks again,

Regards

Tony

Hi Tony,

if you look at the pinout you have posted, you will see that using a three pole plug would short the microphone input to the speaker output...

Try to get an appropriate connector first.

Regards,

Ingo