Service manual Introduction and technical overview 3
Technical overview
The Handle hardware contains the necessary circuitry to perform, measure, and report
tympanograms. It is designed to be portable and rechargeable, and to interface with its
corresponding printer device.
In order to perform a tympanogram, the hardware must support a motor/pump assembly
that is capable of a positive and negative pressure in the ear canal. Simultaneously, a
speaker must drive a monotonic 226-Hz, 85 dB sound pressure into the ear. A
microphone amplifier and A/D converter are included to monitor this sound pressure. The
control of the system (tone and pressure), and display of the tympanogram are
implemented with two micro controllers. The hardware and software must provide a
closed-loop system that maintains the 85 dB sound pressure, regardless of the acoustical
admittance in the ear that changes with pressure.
In addition, the Handle shall be capable of performing fully the above function with a
1000-Hz, 83 dB tone.
In order to support the operator interface, the hardware supports an LCD and keypad with
three keys. In order to interface with the Printer/Charger, the Handle has an IR sensor
communication interface. The Handle is designed to start by the press of a button, or by
insertion into the printer/charger unit.
The Handle hardware system is broken down at the top level into three board-level
assemblies:
1) The MCU Board
2) The Power Supply Board
3) The LCD Board
There are other integral components such as the sensors, motor/pump assembly,
switches, USB port, and IR interface which play significant roles in the plotting of the
tympanogram, the powering up of the unit, and the communication of the unit with a
service computer, ATE testing station, or Printer/Charger.
The Power Supply Board can be broken down into these subsystems:
1. The keypad/power up logic is responsible to start the power supply and interrupt the
master MCU whenever a key is depressed. It also reports which key is depressed and
receives an input from the MCU to keep the system powered up.
2. The battery charger provides a constant current charge to the battery whenever the
Handle is in a printer base. When the battery voltage reaches 4.2 volts, the charger
shall cease charging the battery.
3. The battery detection reports a low battery warning to the micro controller.
4. The negative power supply is an inverting switched capacitor power supply used to
support the analog circuitry and the LCD display.
5. The pump motor control provides a selectable voltage to the motor in either forward
or reverse polarity.
6. The pump motor home detect determines whether the pump diaphragm is above or
below the home position.
7. The valve control provides a fixed voltage to the valve in either the open or closed
polarity.
