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The datasheet for TSOP1738 states absolute max 6 volts, and this is using a 9volt battery - will burn out TSOP. there is no indication of polarity of LED. LED and buzzer are directly across TSOP VCC and OUT pins, meaning TSOP output transistor when on will carry full current of both LED (with NO Current limiting resistor) and buzzer - but data sheet states maximum of 5mA !!Question - which will burn out first LED or TSOP or both ???
Your schematic is in error on the pin numbering of the TSOP1838.You should not tell people to use any old component - for example some components will have lower voltage ratings and could be destroyed.The 10Kohm pullup should not be needed since there is a 30K pull up in the TSOP.I don't see the point of the 47 ohm resistor - it would hardly limit the current and will not drop much voltage since it only feeds the TSOP which only draws a max of 5mA.Similarly, the 1N4148 will not drop much voltage, and if used at all would be better in the main battery feed as a reverse polarity protection.As for the LED flashing on off, etc. If you look at the datasheet for the Vishay TSOP1838 Page 4 Fig 6, you will see the output is high, except when there are brief pulses of IR light modulated at 38KHz, typically from a remote control. With you circuit driving a BC557, it will be on, and the LED also, except for these brief pulses which may be hard to see. You could try stretching the pulses with a NE555 timer (look up data sheet and suggested circuits) and invert signal so LED is only on during (stretched) pulses.As for a line follower, these are usually based on photo transistors to detect the difference between a black line, and a white background. An IR receiver looking for pulses of 38KHz infra red light is unlikely to be of any use.
I was wrong about the LED being mostly on. Because the BC557 is a PNP, it will be mostly off while the TSOP output is high (inactive). When it turns on briefly with the IR pulses, possibly these may be too short to be seen much. Maybe increase the LED current to say 20mA or more, by reducing its 1K resistor, provided you do not exceed the limit for the LED. Or try the NE555 as I suggested.The TSOP1838 is now obsolete. The TSOP32238 is a better choice, and can work on anything from 2.5 to 5.5 volts, so you could use just 2 or 3 AA batteries
The TSOP1838 abs max rating is 6.0 volts, so if 4x1.5 volt AA cells are used, apart from volts drop across 1N4148 diode - this would exceed the safe max voltage.Apart from this what is the purpose of the diode - if it s reverse polarity protection, it would be better places at the input to also protect the transistor.I doubt this circuit could be used for e.g. line following a suggested, since there is a lot of response delay through the TSOP1838 recognizing a 38KHz signalApart from
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