As with every design, there is always room for improvement and requests. I liked to have GPS data stored in the wav file and this calls for a GPS receiver.
In the first boards that were sold there was no space reserved for a GPS receiver, but you can cut-out a small piece of the PCB in te top right corner to make some space for a GPS receiver. A small 18x18mm GPS like the Beitian BN180 or a Ublox of this size works well enough. It has to be small unit with integrated antenna. Others pick up too much noise, You also need to apply some shielding to the Teensy. We do use biderectional communication now, this is not in the schematic, but pin RX of the GPS unit should connect to TX(pin 1) of the Teensy.
Another addition to the data gathering is a temperature sensor. The code supports a dallas temperature sensor.
Maybe the most useful one is the backlight mod. The blacklight modification allows the brightness to be controlled by the Teensy. This works very nice on autorecord mode, this display can be switched off during autorecord to save battery power. For the backlight modification to work properly, you need to have the later version TFT display, the one with Q1 on the display PCB.
The schematic with all these 3 modifications looks like this.