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thirsty003
- 25th November 2008, 02:28
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

b1arrk5
- 26th November 2008, 01:34
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.

inse
- 26th November 2008, 17:10
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

thirsty003
- 27th November 2008, 21:49
Thanks for the reply guys. This is a link to where I got the wiring for the 2.5mm jack - http://pinouts.ru/CellularPhones-Nokia/nokia_headset_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

inse
- 28th November 2008, 05:56
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

thirsty003
- 29th November 2008, 06:29
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

inse
- 29th November 2008, 13:01
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