Data logger and remote control block diagrams

Data logger (5 marks)

A data logger automatically measures and records physical quantities over time.

 Sensors -> Signal    -> MUX -> S/H -> ADC -> Micro-controller
            conditioner                          |   |
                                                 |   +--> Memory
                       Real-time clock ----------+
                                                 +--> Display / PC

1. Sensors convert temperature, pressure, voltage, etc. into electrical signals.
2. The signal conditioner amplifies and filters them.
3. The multiplexer selects one channel at a time, and the sample-and-hold keeps the value steady.
4. The ADC converts it into digital data.
5. The microcontroller adds a time stamp from the real-time clock, stores the data in memory, and shows it on a display or sends it to a computer.

Remote control (5 marks)

A remote control operates a device (TV, AC, fan) wirelessly from a distance, usually with infrared (IR) light, using a coded pulse train.

 Transmitter:
 Keypad -> Encoder IC -> Modulator -> IR LED
                         (38 kHz)
 ......... infrared light .........
 Receiver:
 Photodiode -> Amplifier -> Band-pass -> Demodulator -> Decoder -> Controller
 (IR sensor)                filter                                 / device

Transmitter: pressing a key makes the encoder generate a unique binary code. This code modulates a 38 kHz carrier, and the IR LED sends it as light pulses.

Receiver: the IR photodiode detects the light, and the amplifier and band-pass filter select the 38 kHz signal. (An integrated IR receiver module such as the TSOP1738 contains the photodiode, amplifier, filter and demodulator in one package.) The demodulator recovers the code, the decoder interprets it, and the controller carries out the command (channel change, volume).

Advantages: convenient, low cost, no wires. Limitations: needs line of sight and has a short range (about 10 m). RF remote controls work without line of sight.