water proof ultrasonic
https://www.newegg.com/Product/Product.a...lsrc=aw.ds
even cheaper on ebay.
an industrious lad could could adapt a Car Parking Backup Sensors Kit.
https://www.newegg.com/Product/Product.a...lsrc=aw.ds
even cheaper on ebay.
an industrious lad could could adapt a Car Parking Backup Sensors Kit.