Horn - Welch Allyn SureTemp 986 Service Manual

A.3.6 Horn
Model 986 Thermometer
The horn is activated at the start of a temperature taking cycle, at
the end of a Normal mode temperature cycle, and for various error
conditions.
•
A short duration high pitch single beep indicates normal
operation.
•
A long duration beep, approximately one second, indicates
errors such as temperature out of range during a temperature
measurement cycle.
The horn (LS1) is a miniature piezoelectric speaker with a
resonant frequency of 2 kHz driven by processor square wave.
The horn control signal comes from U1 pin 50 to produce the
audible tones.
Appendix A. Theory of Operation
37