Analog Electronics, 555 timer as VCO and a board by bkorsedal

Hi, We want to make a simple device. It’s a sensor connected to a 555 timer acting as a VCO. There is also a simple NPN transistor which is sometimes turned on. The whole device is operated using usb power from a cell phone and the audio input/output of the cellphone… (Budget: $30-$250 USD, Jobs: Electrical Engineering, PCB Layout)