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Our Complete range of products are Infrared Obstacle Detector and Mobile Bug.
Infrared Obstacle Detector is useful in many applications. One of the most demanding applications can be a tool for blind person. Latest technologies like Automatic (driverless automobiles, train anti-collision, electronic toys like car, train, and robotic gadgets etc.).
The principle involved is infrared (IR) emitter and receiver. When IR emitter emits light and it becomes incident on an obstructing object, it gets reflected. This reflected light is picked up by a sensitive receiver and can be converted to suitable signal to alarm the user regarding the obstacle. Absence or reduction of received light decides the presence or absence of the obstacle.
Modulation is the answer to make our signal stand out above the noise. With modulation we make the IR light source blink in a particular frequency.
Another purpose this modulation solves is to make the circuit more sensitive and able to work with higher range i. e. to detect obstacles from more distance, the light emitter is modulated at about 38 KHz.
About the Circuit :
Mobile Bug is a device that senses the presence of an activated mobile from little distance and gives alarm. The circuit can detect incoming and outgoing calls, SMS and video transmission even if the mobile phone is kept in the silent mode. The moment the bug detects RF transmission signal from an activated mobile phone, it starts sounding a beep alarm and the LED blinks.
The alarm continues until the signal transmission ceases. An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. The transmission frequency of mobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. This handy, pocket-size mobile transmission detector can sense the presence of an activated mobile phone from a distance of one and-a-half meters. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone for spying and unauthorized video transmission. So a circuit detecting gigahertz signals is required for a mobile bug. Here the circuit uses a 0.22µF disk capacitor (C3) to capture the RF signals from the mobile phone.
The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired The disk capacitor along with the leads acts as a small gigahertz loop antenna to collect the RF signals from the mobile phone Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter with capacitor C3 connected between its inverting and non-inverting inputs. It is a CMOS version using gate-protected p-channel MOSFET transistors in the input to provide very high input impedance, very low input current and very high speed of performance. The output CMOS transistor is capable of swinging the output voltage to within 10 mV of either supply voltage terminal. This will upset the balanced input of IC1 and convert the current into the corresponding output voltage. Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stable for easy swing of the output to high state. Resistor R2 provides the discharge path for capacitor C4. Feedback resistor R3 makes the inverting input high when the output becomes high. Capacitor C5 (47pF) is connected across ‘strobe’ (pin 8) and ‘null’ inputs (pin 1) of IC1 for phase compensation and gain control to optimize the frequency response.
When the mobile phone signal is detected by C3, the output of IC1 becomes high and low alternately according to the frequency of the signal as indicated by LED1. This triggers monostable timer IC2 through capacitor C7. Capacitor C6 maintains the base bias of transistor T1 for fast switching action. The low-value timing components R6 and C9 produce very short time delay to avoid audio nuisance. Assemble the circuit on a general purpose PCB as compact as possible and enclose in a small box like junk mobile case. As mentioned earlier, capacitor C3 should have a lead length of 18 mm with lead spacing of 8 mm. Carefully solder the capacitor in standing position with equal spacing of the leads. The response can be optimized by trimming the lead length of C3 for the desired frequency. You may use a short telescopic type antenna. Use the miniature 12V battery of a remote control and a small buzzer to make the gadget pocket-size. The unit will give the warning indication if someone uses mobile phone within a radius of 1.5 meters.
Dilip Bhoyar (Elektrokit)
Keshav Imperial,Shop Nop B-101,B Wing First Floor,Nagpur, , Shani Mandir, Near Shani Mandir, Sitabuldi, Nagpur-440012, Maharashtra, India, Shankar Nagar
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