Remote control

Overview  Circuit description  Protocol  Parts/PCB  Wishlist
The circuit uses an IR receiver chip to receive the IR signal from the remote. The chip includes a bandpass filter and a demodulator, so the output is a logic signal.

The signal is then processed by an Atmel 89C2051 chip that decodes the remote signal and controls the volume pot and relays.
Controller schematic
The controller section is more or less a standard 8051 circuit - the controller chip is basically an updated Intel 87C51 with less pins. Please note that the controller chip has to be programmed. If you buy an AT89C2051 chip it's "empty", so the circuit won't do anything...

The "power off" switch SW1 as well as the output from the IR receiver are connected to the chip's two interrupt inputs. That means the chip can be "put to sleep" most of the time, because signals on those two pins can wake it up.

The address jumper JP5 is used for selecting the RC5 address. Read more in the "Protocol" section. The header JP6 is used for setting options like B+ delay.

BTW, in case you're wondering - 11.0592MHz IS a standard crystal frequency... :-)
Relay driver schematic
This circuit is used for controlling the relays. According to different datasheets the transistor is rated for somewhere between 0.5 and 0.8A.

Most standard relays draw less than 0.1A, so connecting more than one relay shouldn't be a problem. 5 or 6V relays can be used.
Motorpot driver schematic
This part controls the volume pot.

The output pins on the microcontroller are high on reset/power-up, so the motor has to be off with both control inputs high.

The two BC547 transistors Q1 and Q2 make sure the base drive for the output transistors is off on power-up.

When the volume pot has to be moved, the base of either Q1 or Q2 is driven low switching off the transistor. This enables two of the output transistors to switch on. Q3 and Q5 switch on for one direction and Q4 and Q6 for the other direction. If both Q1 and Q2 are switched off at the same time strange things may happen. So that mode of operation is not supported by the standard software ;-)

Here is the complete schematic. I have made both a low resolution file (72dpi) for viewing, and a higher resolution file (200dpi) for printing.

Overview  Circuit description  Protocol  Parts/PCB  Wishlist


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