Ultrasonic remote control for X=ray appts. - has LED indicating both transmitter operation and unacceptable low transmitter battery voltage

摘要

The ultrasonic remote control, for X-ray appts. has an optical indicator (pref. an LED) to indicate when the transmitter's battery voltage falls below a given level. The LED is coupled to the transmitter so that it also indicates when the transmitter is operating. The transmitter may also contain a device to suppress the output of the transmitter when the battery voltage is given below the given level and thereby to prevent the receiver responding. Instead of suppression the device may shift the transmitter's frequency so that it lies outside the receiver window of the receiver.