How many times you needed some remote control to handle some electric device ? many times. There are lot of remote controls like infrared, RF, SMS (like my other circuit) and more. The basic small-range remote controls are 2, Infrared and RF (Radio Frequency). One of the weaks of Infrared is that the signal can not pass the walls. So, if you want to control your garage door, the only way is to use some RF remote control. The circuit (transmitter and receiver) use few components and ordinary (I love few component circuits) . Its easy to build it because you don't have to tune-up any coil or variable capacitor. The RF modules are fix to work in 418MHz area.
I have designe this remote control considering :
If you press the S2 key, the logic of this pin goes to '0' (0V) and AVR awake frome the sleep mode (because PB1 is INT0) and check if pressed the S1 key. If not, the AVR take as pressed key the S2. If yes the AVR take as pressed key the S1.
If you press the S1 key the logic of this pin and PB1 (through 1N4148) goes to '0' (0V). In this case the AVR take as pressed key the S1.
After, calculate the checksum and transmit 4 times the same 4 byte sequence to make sure that receiver takes the data and goes to sleep mode until next interrupt on PB1.
When the INT0 pin (PB1) of AVR goes to 0V, the transmitter TLP434A is working. If you stop press the switch S1 or S2, the TLP is stop working.
example: if byte1=30h, byte2=35h and byte3=03h the 4th byte (chechsum) will be (byte1) XOR (byte2) XOR (byte3) = 30h XOR 35h XOR 03h = 06h.
This method use 4 bytes x 8 bit each = 32 bit length (without start and stop bits). That is mean 1 possibility at 4.294.967.295 to receive the receiver, the same 4 bytes from some other RF device.
This transmitter will work with all 2323 chips but better is AT90LS2323 with working voltage 2.7 - 6 volts.The microcontroller that I use is AT90S2323 with working voltage 4 - 6 volts. Its worked fine with 3v lithium battery.
As antenna you can use ~7cm cable in to transmitter`s box.
The receiver constituted by RF receiver module RLP434A at 418MHz, the microcontroller AT90S2313 and the 2 relays with can handle any electric (or electronic) device up to 10 Amps (the contacts of my relays are 10Amp at 250Volts).
The RLP434A is an RF receiver module with receipt frequency at 418MHz with ASK modulation. There are 2 outputs from this module, the digital, with levels from 0v to VCC (5 volts in our case) and the analog output. Analog output is not used. The transmitter send 4 bytes with 2400bps 4 times and the receiver RLP-434A, collect them and move them to AT90S2313 to RxD pin, PD0.
Two reasons to select AT90S2313 (20pins) instead of AT90S2343 (8pins) is because
As antenna you can use a cable 30 - 35cm long
The power supply
The power supply of RF receiver constituted by 2 voltage regulator, LM7812 and LM7805. The first (12V) its only to power the 2 relays and the 2nd (5V) to power the AVR microcontroller and the RF receiver module. The LED, is voltage indicator and the 4 capacitors are to flattening the voltage.
Usage of transmitter
Power on the receiver and press S1 key to transmitter. You will see that relay on PB0 of receiver will arm. If you press one more time the same key, the relay will dissarm. If you press S2 key from transmitter you will see that relay on PB1 of receiver will arm. If you press one more time the same key, the relay will dissarm. Each key is for 1 relay only.
I choose to drive 2 relays and not only 1 because for some application like garage door 1 relay can handle the door (open-close) and the other to turn-on or off the light of the garage.
New feature added! roll-code. Roll-code function is increase the safety of remote control, because it is change the transmitting code everytime you press any key on the remote control (AT90S2323 circuit) and the RF thief scanners will be useless!
Click here to download the firmware, source code and schematic for AT90S2313 and AT90S2323 microcontrollers
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