thanks for the info , very useful..
ryjobil , sorry, I don't quite what you mean about AC decoupling, and what does your circuit after the amp do?
ok, so I played on a breadboard with a LM324, with a bastl kastle and a 5v power supply. (to avoid damaging a bela board 😉) , the basic concept worked for audio output , I could go +/- 1.1v to 0..3.7v , i.e amplify and offset BUT I found the LM324 was clipping after that... even though its says rail to rail is to supply, (at 7.5v, it clipped around 6v) but I need to check the specs (I'm however going to switch to TL072 when they arrive)
so pretty happy, that can be made to work 🙂
then I went to look at audio input... (so 0..5v to -0.9v to +0.9v)
I thought I could do the same but in reverse, i.e. just use a -ve vref on the opamp, and as its in inverting config, I can scale down... BUT then I suddenly realised I don't have a -ve voltage to supply the opamp , for v- or for the vref.
so I'm not sure how I can generate a bipolar signal for input?
is it possible to 'create a negative voltage', as there are no pin outs no the bela, nor the source I'm using.
EDIT: ive found a max828 ic that creates a -ve voltage, is this what is needed, or am i barking up the wrong tree 😉