Ultrasound Technologies PD1 series, Service Manual

Page: 15 / 75

Ultrasound Technologies Ltd
3.0 Circuit Description
3.1
6 1
Introduction
The circuit has been divided into functional blocks with each block being described separately, the blocks
are as follows:
•
Audio Unit Power Supply
•
Battery Low Indicator
•
Ultrasound Transducer
•
Oscillator and Detector
•
Oscillator and Transmitter Amplifier
•
Receiver and Detector
•
Audio Amplifier
•
Controls and Indicators
•
Unit ON / OFF
•
Battery Low
3.2
6 2
Audio Unit Power Supply
The unit operates from a single 9-Volt dry battery. It is recommended that only alkaline cells
be used. The audio circuit is fed directly from the battery. D1 provides circuit protection from
battery reversal.
The unit is turned on by the membrane switch, which is mounted on the front of the unit.
Closing the switch, grounds the CLK input of U1 pin 3, the output on pin 2 switches on Q2
allowing current to flow into the various circuits.
The unit will remain switched on for approximately 5 minutes (set by C4 and R5) after which it
turns off automatically, unless the user forces the unit off by de-pressing the ON/OFF switch.
3.3
6 3
Battery Low Indicator
U3 is a voltage detector, when the voltage on pin 1 drops below the threshold set by R10 and
R11 (7.3V), the output state changes forcing the LED (D2) to illuminate.
3.4
6 4
Ultrasound Transducer
The ultrasound transducer operates on the pulse wave Doppler principle. There are a number
of transducer frequencies suitable for different applications, however the basic operating
principles are identical.
Each transducer consists of a pair of piezo ceramic crystals, each crystal pair is arranged as
a transmitter and receiver, the ultrasonic output beam is focussed through a lens or faceplate.
©Ultrasound Technologies Ltd Page 11 of 32
PD1 / FT120 service manual Issue 3 January 2007