Low battery voltage indicator circuit for a metal detector

• US 4,488,115 A
• Filed: 09/30/1982
• Issued: 12/11/1984
• Est. Priority Date: 11/12/1980
• Status: Expired due to Term

• Current Assignee: Garrett Electronics Incorporated
• Original Assignee: Garrett Electronics Incorporated
• Inventors: Podhrasky, Robert J.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/429,489
• Time in Patent Office: 803 Days
• Field of Search: 324/326-329, 324/133, 324/426, 324/433, 324/436, 455/29, 455/115, 455/226, 340/636
• US Class Current: 324/329
• CPC Class Codes: G01V 3/107 using compensating coil or loop arrangements

Abstract

A metal detector is disclosed which has a transmit coil, a receive coil, and circuit means for detecting metal objects due to a change in the magnetic coupling between the coils. Circuit board arrangement techniques are disclosed which enable the close placement of the transmit and receive coils and the circuit board, thereby allowing packaging of the metal detector in a small package. A low battery voltage indicator circuit is provided to warble an audio indicator signal to indicate sufficient battery voltage. In the event the battery voltage drops below a certain level, the warbling of the indicator signal ceases and a steady tone is generated thereby indicating a low battery voltage condition.

Claims

1. A low battery voltage indicator circuit for providing an audio indication of battery status for a portable metal detector which is powered by a battery and has an audio output for indicating detection of an object to an operator, comprising:

a first audio frequency oscillator for producing said audio output in response to a signal generated by said metal detector upon detecting an object,

a second audio frequency oscillator having an oscillation frequency lower than that of said first audio frequency oscillator, said second audio frequency oscillator connected to modulate said first audio frequency oscillator to produce a warbling effect for said audio output,

a voltage level detector connected to monitor the voltage of said battery and produce a selected output when the voltage of said battery drops below a preset voltage, and

means connected to said voltage level detector for receiving said selected output and further connected to said second audio frequency oscillator for permitting said second audio frequency oscillator to modulate said first audio frequency oscillator when the voltage of said battery exceeds said preset voltage and for disabling said second audio frequency oscillator upon receipt of said selected output when the voltage of said battery goes below said preset voltage to terminate the modulation of said first audio frequency oscillator by said second audio frequency oscillator whereby the generation of a non-modulated output from said first audio frequency oscillator indicates a low battery voltage condition to said operator.

2. The low battery voltage indicator circuit of claim 1 wherein said voltage level detector comprises a transistor having the emitter terminal thereof connected to a terminal of said battery, the base terminal thereof coupled to a reference voltage and the collector terminal thereof coupled to a common node, said selected output produced at said collector terminal.

3. The low battery voltage indicator circuit of claim 2 wherein said means for receiving said selected output comprises a diode connected between said collector terminal and said second audio frequency oscillator for applying a selected state to disable said second audio frequency oscillator.