We all use remote control handsets for controlling various household devices such as TV, AC, Music systems, curtains etc, and sometimes we seem to have problems with these devices, or even a newly purchased remote controller unit occasionally seem to malfunction, and identifying the issue becomes quite difficult for us.
This simple 2 transistor circuit will allow you to check the response of any remote control handset and help you to verify whether or not it is working OK, or needs to be replaced with a new.
Most of the time a low battery or a loose battery connection becomes the main issue which causes a remote handset to malfunction, however if you have a new battery installed and still the device doesn't work efficiently then perhaps this simple remote tester circuit could be used for identifying the fault.
Using a Two Transistor Circuit
A simple remote tester circuit using just 2 transistors can be seen in the above figure. The working of the design is self explanatory.
When the remote control handset's button is pressed and pointed towards the photodiode of the circuit, the photodiode begins conducting and allows a few mV to pass through it.
These tiny electrical signals in the form millivolts reach the base of the NPN BC547 which responds to these signals and in turn begins conducting. However, its amplification is significantly low at this stage.
Therefore another transistor in the form of BC557 is attached with the collector BC547 to enhance or boost the amplification to a level sufficient enough to illuminate an indicator LED.
The amplified signals from the photodiode ultimately is boosted to illuminate the attached red LED connected across the collector of the BC557 and the ground line.
The LED lights up and begins flashing as per the remote control's internal pulsed waveform or the programmed signal code.
The 1N4007 ensures some degree of filtration from stray signals and helps the LED to remain shut off during standby positions.
Still you may find the LED glowing dimly if an ambient light is incident on the photodiode, since all forms of white light will have a certain amount of infrared waveform which can affect the photodiode performance.
Using an Opamp Circuit
The above design can be also experimented with an opamp circuit as shown below:
The remote control tester above using an opamp also looks pretty straightforward.
An ordinary opamp 741 is employed here for the detection. It is configured as a comparator. Its inverting input pin#2 is used as a reference level, and is set by fixing the connected preset.
The photodiode can be seen connected across the the non-inverting pin#3 and the positive line.
The preset is adjusted such that in normal condition when no signal is being received by the photodiode, the LED at pin#6 stays just shut off.
This is actually very easy, just switch ON power and begin adjusting the preset to-and-fro, and set it at a point where the LED just remains shut-off.
Next, point a TV remote control handset towards the photodiode, press any of the buttons of the remote control, you will instantly find the LED blinking in response to the remote control's coded IR signals.
Using TSOP1738 IC
The TSOP17XX series infrared sensors are specially designed for IR remote control operations. Even our TV sets use this versatile and efficient device for sensing and decoding IR signals and for executing the necessary commands.
A simple remote tester can be built using the same IC, through the following schematic:
Again the remote tester design using a TSOP1738 appears extremely straightforward.
The connection arrangement of the TSOP IC is in its standard form, rest of the circuit is as simple as it can be. Just a couple of transistors are enough to get the circuit working in the most versatile way.
The great feature of this circuit is its immunity to noise and ambient light, not forgetting the sensitivity and range too. The detection range is actually awesome, you can point the remote handset to an opposite wall and still get the LED to respond efficiently from the reflected IR rays.
The aim of the above explained remote tester circuits is to show how a simple IR circuit can be used for activating an LED in response to IR rays from any ordinary IR remote control system.
The LED can be easily replaced with a relay for accomplishing more complex jobs as per a given application requirement, or as per user preference.
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