Ultrasonic distance meter using arduino

Hi, I am using Ma405s , Ma405r (Transmitter and Receiver) in my project. The specifications are:
description: ultrasonic sensor transducer - receiver
max. input voltage: 20Vrms
operating temperature: -4°F to +185°F
range: 0.6 to 20ft
nominal frequency: 40kHz
sensitivity: -67dB min.
sound pressure: 112dB min.
I am making a distance meter using this ultrasonic transmitter and receiver.
i have made the transmitter circuit and the receiver circuit and would like to interface it with the Arduino. Is it true that i need to amplify the receiver output before giving it to the arduino? If so, how can i do it?
It would be very helpful if u could als guide me as to how can i connect the transmitter and the receiver with the arduino?

Take a look at the datasheets for the Maxbotix sonars. They have a schematic
that shows the amplifier on the receive transducer. Simple opAmp ckt.

I had a look and now i m pretty clear as to how to connect the receiver circuit with the arduino. Coming back to the receiver circuit, i m nt getting a steady output. I have used two LM386 ICs, the first one giving a gain of 50 while the second giving a gain of 200. But the second goes into saturation. I donot know how can i achieve a constant output. Can i use AD620 ? or can u suggest me with some other alternative. Please help me out.