This car lock defroster is meant to save as an aid in opening car locks which often tend to get jammed, especially during the winter months. The circuit basically consists of a small heating element around the barrel which is triggered automatically by the accompanying circuit which controls its switching.
Although a simple monostable timer could have been used, but this would trigger the circuit even during summers, precisely every time the door is opened, thus causing unnecessary drainage of batteries. Using an on/off switch would defeat the whole purpose of the device. Switch S1, shown in the accompanying circuit, is a simple normally open micro switch that if fixed in such a way that every time the door handle is moved, it is pressed while attempting to open the door five times, the heater gets activated for a period of several seconds, after which it discharges.
The circuit uses a 4017 decade counter which is clocked forward by S1. When S1 is pressed five times, output q5 goes high. When this happens, the counter should reset as it is connected to reset terminal, But, a delay of up to 20 seconds, adjustable through P1 is provided by C1,R1,D1 and P1. In the meantime the relay Re 1 remains activated, which in turn, activates the heating resistors R1 a and R1 b.
The heater resistors, which are wire wound, should be fastened to the barrel using tinned metal wire and then covered with metal foil. The circuit consumes very low current, in the order of a few hundred micro amperes. So it can be left directly connected to the batteries.
Although a simple monostable timer could have been used, but this would trigger the circuit even during summers, precisely every time the door is opened, thus causing unnecessary drainage of batteries. Using an on/off switch would defeat the whole purpose of the device. Switch S1, shown in the accompanying circuit, is a simple normally open micro switch that if fixed in such a way that every time the door handle is moved, it is pressed while attempting to open the door five times, the heater gets activated for a period of several seconds, after which it discharges.
The circuit uses a 4017 decade counter which is clocked forward by S1. When S1 is pressed five times, output q5 goes high. When this happens, the counter should reset as it is connected to reset terminal, But, a delay of up to 20 seconds, adjustable through P1 is provided by C1,R1,D1 and P1. In the meantime the relay Re 1 remains activated, which in turn, activates the heating resistors R1 a and R1 b.
The heater resistors, which are wire wound, should be fastened to the barrel using tinned metal wire and then covered with metal foil. The circuit consumes very low current, in the order of a few hundred micro amperes. So it can be left directly connected to the batteries.
Schematic : The car lock defroster uses a novel way to produce heat
