GB2395292A - Automatic vehicle windscreen defrosting circuit - Google Patents

Abstract

A circuit for automatically activating defrosting systems of a vehicle's front and rear windscreens may comprise a programmable microchip 5, a timer switch 4 and a temperature sensing switch 3. The timer switch 4 may be preset to activate the defrosting systems before a driver is due to begin a journey, and the temperature sensing switch 3 may be used to ensure that the defrosting systems are only activated when ambient temperature is below a predetermined level. When a preset time is reached, timer switch 4 may close and, if ambient temperature is below the predetermined level, temperature sensing switch 3 may also be closed. With both switches closed, the microchip 5 may provide a voltage output 6 to activate the windscreen defrosting systems for a predetermined duration.

Description

Timed Automatic Windscreen Beater Defrost Circuit The invention is based

upon the manipulation of existing circuitry used in all cars to clear front and rear windscreens of frostlmist prior to a journey.

l:)uring the winter months, nighttime temperatures often dip well below freezing. This results in frost or ice forming and settling on car windscreens, which must be cleared for visibility prior to the start any journey (for example before travelling to/from work).

Currently this is usually done by the driver using ice scrapers and/or deicing fluid.

This invention in the form of additional circuits and components eradicates the necessity to scrape windscreens or defrost them when the engine warms up by allowing preset timed operation of the windscreen heaters prior to the driver entering the car, therefore preparing the car for immediate use by the driver, and avoiding unpleasant and time . consurmng scraping.

The heart of the additional circuitry is to be a programmable chip (microcontroller) to which low level programming code can be written. This chip will perform the activation of relays in the windscreen heater circuits, and will activate these circuits for a given duration only when the required input conditions exist, i.e. the temperature is low enough and the drivers preset time has been reached.

Timed activation is set to whatever time the driver desires in similar fashion to setting an alarm clock. This also allows for the function to be switched out of use during summer months. The circuit will be able to operate with element heated or fan operated front windscreen heaters and all rear windscreen heaters.

A description of the invention follows hereafter with reference to the accompanying

circuit diagrams of the circuit in which: FIGURE 1 shows the control circuit for the activation of the windscreen heaters.

FIGURE 2 shows the power circuit for the windscreen heaters.

As shown in figure 1, the control circuit comprises of the car battery 1 connected negative to the car frame 2 and supplying two inputs to the programmable microcontroller chip 5 via a temperature sensing switch 3 or the preset timer switch 4. An output 6 from the chip is then provided.

Figure 2 shows the power circuit also connected to the car battery 1 supplying the existing circuitry for the rear windscreen heater 13 via fuse 7, ignition switch 10 and push button switch 11.

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Additional feeds for the rear windscreen heater 13 and front windscreen heater 12 are established via fuses 7 and relay contacts 9. The relay coils 8 operate the contacts.

Supply to both of the inputs of the programmable microcontroller chip 5 in figure 1 have to be present to obtain voltage at the output 6. For this to occur, the temperature sensing switch 3 and preset timer switch 4 must both be closed, indicating that the temperature has dropped to a certain predetermined level and the drivers preset time has been reached.

The programmable microcontroller chip will maintain voltage at the output 6 for a predetermined duration. This output 6 will supply voltage to operate the relay coils 8 in the power circuit figure 2, which in turn will close relay contacts 9 to supply both front and rear windscreen heaters 12,13 bypassing the ignition switch 10 and push button switch 1 1.

When the predetermined duration of supply to the output 6 from the programmable microcontroller chip 5 in figure 1 is complete, the output voltage is removed and the relay coils in figure 2 are de-energised, removing the supply to the heaters after the windscreens have been defrosted.

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Claims (5)

1. I. An electrical circuit which enables the automatic activation of car front and rear windscreen heaters for the purpose of defrosting or deicing.
2. 2. An electrical circuit as claimed in claim 1 where circuit activation and operation is controlled by a programmable chip.
3. 3. An electrical circuit as claimed in claim 1 or claim 2 where the driver can preset the timed activation of the circuit.
4. 4. An electrical circuit as claimed in any preceding claim where the activation of the circuit depends on the ambient temperature.
5. 5. An electrical circuit substantially as herein described and illustrated in the accompanying drawings.

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