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