Thermostat having simple battery level detection

• US 5,238,184 A
• Filed: 09/30/1991
• Issued: 08/24/1993
• Est. Priority Date: 09/30/1991
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Adams, John T.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US07/769,043
• Time in Patent Office: 694 Days
• Field of Search: 324/436, 236/46 R, 236/94, 165/12, 165/11.1, 340/636, 136/293
• US Class Current: 236/94
• CPC Class Codes: G05D 23/1905 associated with tele control
• CPC Class Codes: G08B 29/181 due to failing power supply

Abstract

A thermostat having a simple battery level detection circuit. The output of an oscillator, having a frequency dependent upon the battery level, is compared to the output of a battery level independent time base. If the two outputs are not in a predetermined relationship, all connected HVAC equipment is shut off.

Claims

1. In a thermostat for controlling HVAC equipment having a battery, the battery having a power level, battery testing means, comprising:

a time base generator producing a first signal having a frequency substantially independent of the power level;

an oscillator producing a second signal having a frequency substantially dependent upon the power level;

a comparator connected to said time base generator and said oscillator, said comparator shutting off said HVAC equipment if said first and second signals are not in a pre-determined relationship.

2. The battery testing means of claim 1, wherein:

the microprocessor has an internal battery level checking means for determining when battery level drops below a first power level, said internal battery level checking means producing a low level signal, said battery level checking means being connected to said comparator; and

said comparator is activated upon receipt of said low level signal.

3. The battery testing means of claim 2, further comprising:

an indicator connected to said internal battery check means, said indicator providing indication to an operator that the battery has dropped below said first level.

4. A thermostat, comprising:

temperature sensing means for producing a temperature signal representative of space temperature;

a battery having a power level;

temperature responsive means connected to said temperature sensing means for comparing said temperature signal with a desired temperature signal, said desired temperature signal being representative of a desired space temperature, said temperature responsive means producing a control signal representative of a difference between said space temperature and said desired space temperature;

a first battery level check comprising;

a time base generator producing a first signal which is substantially independent of said power level;

an oscillator producing a second signal which is substantially dependent upon said power level; and

a comparator connected to said time base generator and said oscillator and producing a third signal if said first and second signals are not in a pre-determined relationship, said third signal causing said temperature responsive means to become inactive.