This bat detector is a showcase of how functionality and physical design can be combined in a beautiful way. It traces the sonar messages of all kinds of bat species in a frequency range of 20kHz to 120kHz by the use of a special microphone. The incoming bat signals are strongly amplified and then converted to the human audible range by an analog mixer design. The device has two operating modes: 1. the user selects the frequency to listen to, and 2. the user picks a high and a low frequency and then lets the device alternate between them. The alternation time can then be manually stretched in a number of positions between 2 seconds and infinity, and a short, soft high or low beep indicates which frequency spectrum is listened to. The software controlling this device is modeling a State Machine, allowing the user to switch seamlessly between operating modes.
The design of the user interface reflects the operation modes: the purpose of the right side turning dial depends on the operation mode (machine state) that is controlled by the sweep button:
The PCB is built from stripboard (see here for the PCB design) and looks in practice like this:
I originally developed this bat detector as a Philips EE project, and all technical details on the final electronics and software design can be found there:
