Ultrasonic Module 

Circuit Description
-------------------

The circuit may be divided into the following modules:

1) The Microcontroller
2) The Recieving Module
3) Transmitting Module 1 ( For longer range )
   or 
   Transmitting Module 2 ( For medium range )

------------------------------------------------------------

1) The Microcontroller 
----------------------

This part of the circuit consists of the follwing:

a) The Microcontroller

The pin configuration and description can be summarized below:

Pin 1 - Not Connected 
Pin 2 - Rxd (Serial Data Recieve)
Pin 3 - Txd (Serial Data Transmit)
Pin 4 - Gnd (Power Supply: Ground)
Pin 5 - T2  (A pulse train of 40kHz is generated here : COnnected to the input of Transmitting module)
Pin 6 - T1  (A pulse train of 40kHz is generated here : COnnected to the input of Transmitting module)
Pin 7 - INT (External interrupt pin - Connected to the output of recieving module)
Pin 8 - Vcc (Power Supply: +5V)


b) The 4-Pin connector

The 4-Pin connector enables serial data communication with the microcontroller and provides power supply of +5V to the circuit.

------------------------------------------------------------

2) The Recieving Module
-----------------------

The recieving module filters and amplifies the signal recieved by the ultrasonic reciever. The main components are:

a) The ultrasonic reciever

b) The 40kHz band pass filter circuit (using UAF42)

c) The non-inverting amplifier (using OPA2356 OP-Amp)

d) The voltage-level shifter

The filter IC UAF42 requires supply levels of +12V and -12V. The power supplied to the circuit however is only +5V. So a voltage level shifter module is used for this purpose. 

The ultrasonic reciever is connected to the UAF42 circuit which is a Band Pass Filter of center frequency 40kHz. The output of the filter is connecting to an amplifier circuit which amplifies the signal level from a few milli-volts to between 0 and 5 volts.

The output of the recieving module (that is, the output of the amplifier circuit) is connected to Pin 7 (External Interrupt) of the microcontroller.


------------------------------------------------------------

3) The transmitting module
--------------------------

Depending on the range requirements, either transmitting module 1 or 2 may be used. Each is explained seperately below:

a) Transmitting module 1

This may be used if a long range (approx. 10 meters) is required. In this case only one of the T1 or T2 signals generated from the microcontroller may be used. The ultrasonic transmitter is connected to the secondary of the transformer while a transistor drives the primary of the transformer. The signal is connected to the base of the transistor as shown in the circuit. In this case the collector needs to be given a supply voltage of +5V

b) Transmitting module 2

This is to be used if a medium range is required. A MAX232 level shifter is used to step up the voltage levels of the signals T1 and T2. The transmitter is connected to the output of this module(Pins 14 and 7 of MAX 232).
