Mutchus

Protect your valuable laptop against theft using this miniature alarm generator. Fixed in-side the laptop case, it will sound a loud alarm when someone tries to take the laptop. This highly sensitive circuit uses a homemade tilt switch to activate the alarm through tilting of the laptop case. The circuit uses readily available components and can be assembled on a small piece of Vero board or a general-purpose PCB. It is powered by a 12V miniature battery used in remote control devices. IC TLO71 (IC1) is used as a voltage comparator with a potential divider comprising R2 and R3 providing half supply voltage at the non-inverting input (pin 3) of IC1. The inverting input receives a higher voltage through a water-activated tilt switch only when the probes in the tilt switch make contact with water. When the tilt switch is kept in the horizontal position, the inverting input of IC1 gets a higher voltage than its non-inverting input and the output remains low. IC CD4538 (IC2) is used as a m...

People often forget that many voltage regulator ICs have an upper limit (usually 35 V) on the input voltage they can handle. That applies primarily to types with a fixed output voltage. Adjustable voltage regulators also have a maximum voltage specification, in that case between the input and output (commonly 40 V). The input voltage must thus be limited to that level in a fault situation in which the output is shorted. This circuit shows a way to allow such regulators to be used in situations with higher input voltages. Although the solution consists of an additional three components, it is simple and can be built using commonly available components. Voltage Regulators Protector Circuit Diagram The voltage across the regulator is limited by the combination of T1 and zener diode D1 to a value that allows the regulator to work properly with loads up to the maximum rated load. R1 provides an adequate operating current for D1 and the bias current for T1. It’s a good idea to use a Darlingt...

The circuit described here can be used to  ensure  that  a  12 V  sealed  lead  acid  (SLA)  gel battery isn’t discharged too deeply. The  principal part of the circuit is a bistable relay,  which is driven by the output of an op amp.  Lead Acid Battery Protector Circuit Diagram The battery voltage is first reduced via D1, R1,  P1 and R2, and then continuously compared  with a reference voltage set up by diode D2.  When the battery discharges too much and  its terminal voltage drops below the level  set by P1, the output of the opamp becomes  High, which causes the relay to toggle. This  in turn isolates the load from the battery. The  battery can be reconnected via S1 once the  battery has been replaced or recharged.  The relay used in the prototype is a 5 V bistable type made by Omron (G6AK-234P-ST-US  5 VDC). The two windings of the relay each  have a resistance of...