I want to connect an old phone to a Bluetooth module. I first thought to use the original speaker and microphone, but the quality is quite bad, so I decided to rip apart an old PC-microphone and cheap headphones.
The microphone is a simple electret condenser, the headphone speaker (don't know exact model) is two-wire and measures 31 ohm, and I use the BTM510 Bluetooth module. The Bluetooth datasheet states that it can drive speakers with a minimum impedance of 16 ohm directly.
The problem is that the old phone horn uses a common ground for the (original) speaker and microphone, so there are only three wires running up the cord. From what I found on the internet, not all amplifiers can have their audio- connected to ground, but I would really like to keep the original three-wire cord.
Is it possible to connect the speaker and microphone to the module with the speaker negative side connected to ground, like in the following manner (with Vcc being about 3.8V). Would this work properly? Would I loose half the power of the speaker?