I want to measure the depth the arduino is at in some water and also the distance to the bottom. The sensors and arduino will be underwater. I was thinking a pressure sensor for the depth and a ultrasonic sensor for the distance to bottom. I was thinking of this for the ultrasonic sensor Maxbotix Weather-Resistant Ultrasonic Rangefinder [MB7092 XL-MaxSonar-WRMA1] : ID 1137 : $99.95 : Adafruit Industries, Unique & fun DIY electronics and kits . Not sure on what to use for the pressure sensor, it would have to be waterproof or can i waterproof them afterwards? Any advice on these sensors or suggestions?
I have found a pressure sensor: SparkFun Pressure Sensor Breakout - MS5803-14BA - SEN-12909 - SparkFun Electronics Although it is not waterproof i have seen various articles online where they spray or "pot" the boards so it is waterproof. I would be aiming to do that obviously leaving the actual sensor exposed. Has anyone had any experience doing that? As for the ultrasonic sensor i haven't really found any different examples only the one from adafruit... Which i can afford but seems pretty expensive.
Just looked at the link you posted for the pressure sensor. OMG that's a lot of money to risk dropping in water. I'd be inclined to attempt to make my own. Is size an issue?
The echo sounder could be an interesting project in it's own right. I'd start with a small speaker (perhaps out of an old laptop or mobile phone) and a microphone (possibly from the same laptop or phone), Create a basic oscillator using a 555 chip. A very simple tuned circuit on the microphone feeding a transistor, and you'd practically have a digital high when the tone is present.
Sound travels a LOT better in water so you don't need much power.