Every Home requires a Remote Tester because we are now using a number of Remote controlled Gadgets like TV, Home theater system etc. The Remote handset emits invisible pulsed Infrared rays which controls the functions of gadgets based on the pulsed data arriving. The Infrared Receiver LED (Rx) or a Photo module in the gadget senses this pulsed IR rays and makes the gadgets function accordingly. The Infrared Emitter LED (Tx) in the remote handset is similar to an ordinary LED but emitting Infrared rays in the wavelength around 900 nanometres. This wavelength is beyond our Spectral response, so we can’t see it. So what will do to confirm whether the Remote handset is working or not. If this tester is not available, we have to go to the shop to purchase a new one. Sometimes, it may be due to battery problem. Let us make one tiny Remote tester. It blinks an LED if the Remote is good. Its cost is only Rs.25.
We need the following components to make the Remote Tester
Its working is too simple. We are using an Infrared Receiver (Rx) to sense the IR rays from the Remote handset. The Infrared Tx (Transmitter) and Rx (Receiver) pair is available just for Rs.5. Purchase one pair and use only the Rx. It works similar to a Photodiode in the Reverse biased condition.
See what is happening. In the circuit, the IR receiver LED is connected in the reverse biased mode with the resistor R1. The Cathode of IR (Rx) goes to the base of the PNP transistor BC557. The Emitter of T1 is connected to the Positive rail, while its Collector has a Red transparent LED with the current limiting resistor R2.
So in the standby condition, the Red LED remains off. Why this? The IR (Rx) is not getting IR and it is in the non conducting mode. At the same time, the base of T1 remains high through R1. So T1 remains off. LED also remains off due to the lack of power from T1. But when we focus the Remote handset and any button is pressed, if the remote is good, it emits IR rays. When these IR rays fall on the IR ( Rx ) of the circuit, it conducts. This takes the base of T1 to ground potential and T1 conducts. The Red LED now gets power and it blinks based on the on/off of T1 because the IR (Rx) is getting pulsed IR rays.
This can also be used to test various projects using IR transmitter circuits. Since the working of IR LED is not visible, this will help to confirm whether the circuit is emitting IR rays or not. It can also be used as an IR (Rx), Photodiode and Phototransistor Tester.
Note – The IR (Rx) conducts when strong light such as sunlight falls on it. So test in a low light area or enclose the IR (Rx) in a black tube.
Here is a Trick to Test Remote without a Tester .Even though, the IR is invisible to human eye, a Camera can see it very well. Just focus the Mobile phone camera towards the IR LED of Remote and press any key of the Remote. You can see the Pink light flashing from the Remote IR LED. It is the Infrared rays.Well it is working.