Long-distance infrared emission circuit diagram analysis

Here's the long range/long range IR transmitter circuit to provide extra power to your IR transmitter. Most infrared remote controls do the job reliably within a range of 5 meters. If you design your IR transmitter to operate well over extended distances (e.g. 10 meters), the circuit complexity increases. To double the distance from 5 meters to 10 meters, it is recommended to increase the transmit power by 4 times.

If you want to achieve a highly directional infrared beam (a very narrow beam), you can appropriately use an infrared laser pointer as the infrared signal source. Laser pointers are easily available in the market. Even so, with the very narrow beam emitted by a laser pointer, you still need to be particularly careful lest a slight shake of the gadget might alter the beam positioning and cause loss of contact. Here's a really simple circuit that will get you quite a distance. It utilizes three infrared emitting LEDs (IR1 to IR3) connected in series to increase the radiated power. Additionally, to increase directionality and power density, you can build an IRLED inside the flashlight's reflector.

To improve the performance of the circuit, a MOSFET (BS170) is used, which operates as a switch, thus minimizing the electrical power losses that can occur when using transistors. To prevent any dips during its "on"/"off" operation, a 100uF storage capacitor C2 is used across the battery supply. If the infrared transmitter is powered by ordinary batteries, its benefits will be more obvious. Capacitor C2 provides additional charge during the "turn on" process.

Since MOSFETs exhibit a large capacitance between the gate-source terminals, a specific driver arrangement has been built implementing an NPN-PNP Darlington pair of BC547 and BC557 (as an emitter follower) to Prevent gate drive input distortion. The data used for transmission (CMOS compatible) is used to modulate the 38kHz frequency generated by the CD4047 (IC1). Even so, in the circuit shown here, tactile switch S1 has been used to modulate and transmit the IR signal.

Assemble the circuit on a standard PCB. Use switch S2 for power "on"/"off" control. Commercially available IR receiver modules (e.g., TSOP1738) can be used to efficiently receive the transmitted IR signal.