diagram ingram

Nearly always when a remote control doesn’t work, the underlying problem is elementary: the unit does not emit light. The cause may be dry solder joints, defective LEDs etc., but also a flat battery (perhaps due to stuck key). The human eye is unable to perceive infra-red light. By contrast, an ordinary photo transistor like the BP103 has no problems working in the infrared spectrum, so in the circuit here it simply biases the BC558 which, in turn, makes LED D1 flash in sympathy with the telegram from the remote control. The preset in the circuit determines the sensitivity.

As I was developing my IR Extender Circuit, I needed to find a way of measuring the relative intensities of different Infra red light sources. This circuit is the result of my research. I have used a photodiode, SFH2030 as an infra red sensor. A MOSFET opamp, CA3140 is used in the differential mode to amplify the pulses of current from the photodiode. LED1 is an ordinary coloured led which will light when IR radiation is being received. The output of the opamp, pin 6 may be connected to a multimeter set to read DC volts. Infra red remote control strengths can be compared by the meter reading, the higher the reading, the stronger the infra red light. I aimed different remote control at the sensor from about 1 meter away when comparing results. For every microamp of current through the photodiode, about 1 volt is produced at the output. A 741 or LF351 will not work in this circuit. Although I have used a 12 volt power supply, a 9 volt battery will also work here.