| This unit is used for remote control using infrared over a distance of up to about 10m. Depending on the circuit details, it can provide simple on-off operation, or it can receive data from a hand-held remote control or a PIC. |
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How does it operate?
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Circuit for detecting any IR pulses
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. The infrared photo module in the Livewire circuit is a socket with the same pin arrangements as the actual detector, not a functioning detector. |
Hand-held infrared remote controls used for TV, hi-fi’s etc. send out bursts of pulses of infrared at 38kHz.
Infrared photo modules are specially ‘tuned’ to pick up these pulses.
These remote controls produce bursts of pulses of infrared at 38kHz. When the detector receives these, its output signal falls to 0V i.e. a digital low (when there are no infrared pulses the signal from the detector is a digital high). The other components in the circuit smooth out the bursts, so the output signal from the subsystem stays low while any button on the remote control is pressed.
The output signal can be fed to a further subsystem, such as a PIC or a CMOS 4000B IC. |
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Circuit for use with Sony IR remote control
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. The infrared photo module in the Livewire circuit is a socket with the same pin arrangements as the actual detector, not a functioning detector.
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The circuit on the left uses the same infrared photo module, but it is able to receive data (not just a single on/off signal) and needs to be linked to a PICAXE microcontroller.
The signal can come from either a Sony TV remote control, or it can be generated by a PICAXE 08M microcontroller.
A special command called ‘InfraIn’ in PIC Logicator and PICAXE Program Editor is used to check the data. The InfraIn command waits until it receives a code from the infrared detector. This happens when a button is pressed on the TV remote control (or a code is sent from a PICAXE 08M). So pressing different buttons on the TV remote can give different results on the receiving PIC.
Full details of the operation of this system are given on this web site.
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Two infrared photo modules are available. They are almost identical except for the voltage supply they require.
The HRM138BB5100 operates reliably with a supply voltage in the range 2.7V to 5.5V and so is suitable for battery operation. The HRM538BB5100 is a few pence cheaper but needs a supply voltage in the range 4.5V to 5.5V and so is only suitable for use with a 5V power supply.
The HRM138BB5100 is available from Rapid Electronics (order code 55-0902). The HRM538BB5100 is available from Rapid Electronics (order code 55-0901) and from Revolution Education (order code LED020). It is also in the Revolution AXE040 kit (which includes a Sony IR TV remote control). |
Possible applications
- Low cost remote control at a distance of up to about 10m
- Detecting a moving object by checking if it has interrupted an IR beam
Making
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Pins of IR photo module
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How part of the PCB for the circuit for detecting any IR pulses might look
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Testing
To test the circuit for detecting any IR pulses, make sure that the signal going out (on the green PCB track) is high when no IR signal is being transmitted, and goes low when a button on the remote IR control is pressed.
To test the circuit for use with a Sony TV IR remote control, make sure that the signal going out (on the green PCB track) is high when no IR signal is being transmitted. Connect a PICAXE microcontroller to the detector. Write a short test program to turn an output device off and on when the correct IR code is detected. Extend this to test the response to different buttons.
Fault finding
If there is a fault, check that:
- The detector is the right way round
- The voltage on pin 2 of the IR photo module is low (0V)
- The voltage on pin 3 is high (the supply voltage)
- The capacitor and photo module are the right way round
- The diode (if used) is the right way round
If there is a fault, check the tracks and solder joints.
Alternatives
- Remote control can be achieved with the Rapid 4-bit IR remote control and the TEP Infrared remote control system. These are more expensive than the systems described here, but they can be used with any PIC or other integrated circuits.
- A high power IR LED and detector can provide remote control. This is inexpensive, but will only work reliably over about half a meter and is disturbed by bright light.
- Remote control can also be achieved with radio which has a longer range and can pass through walls and doors. But this is more complicated and expensive.
- Remote control can also be achieved with ultrasound
Web links
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