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modnexaremote [2009/06/29 22:52]
sestst
modnexaremote [2018/11/03 02:59]
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-{{ :​nexatotal.jpg |Nexa Receiver and Transmitter}} 
  
-====== Generic 433 MHz transmitter ====== 
-The [[audioprotocoltransmitter | AudioProtocolTransmitter]] module, can encode digital protocols as audio signals from the sound card/audio output from a PC. To be able to transmit the signals, some kind of hardware is needed. This is a description of how to build a generic RF-transmitter working on the 433MHz band. 
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-===== Step 1, Signal Level ===== 
-The first step is to transform the low level AC output signal from the sound card to a digital signal strong enough to drive a transmitter. This is done with a simple OP-Amp circuit as follows: 
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- {{ :​transmit.png |Transmitter schematics }} 
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-The OP-Amp can be any general purpose type which can handle single power supply and high power output. 
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-===== Step 2, Transmitter ===== 
-The easiest way to build the transmitter is to modify an existing one. I took an ordinary Nexa remote control, disconnected its logic chip and hooked up the output of the OP-Amp to the transmitter stage of the remote control. 
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-This is how the remote control looks (to the right): 
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-{{ :​nexatotal.jpg |Nexa Receiver and Transmitter}} 
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-Disconnecting the logic chip requires a steady hand, here are the steps: 
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-==== Locate the data output ==== 
-Locate the signal output pin from the chip. This is where the digital protocol is sent to the RF-transmitter stage. 
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-{{ :​nexaremote1.jpg | Output pin}} 
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-==== Disconnect the output pin ==== 
-Cut the track on the board from the output pin and the pin next to it, remove the surface mounted capacitor. This is a bit tricky, because the tracks are small... 
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-{{ :​nexaremote2.jpg | Disconnect output pin}} 
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-==== Connect our signal ==== 
-The final step is to connect our digital output signal (from the OP-Amp) to the RF-transmitter. I used the hole in the PCB as guide and soldered it to the connecting pad of capacitor I removed: 
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-{{ :​nexaremote3.jpg | Connect our signal to the transmitter}} 
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-Now any output from the sound card will be transmitted as a 433MHz signal, and we have a generic remote control transmitter! 
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-===== Step 3, Package ===== 
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-There are many ways to hook this up to the computer. I used a cheap USB-headset converter as sound card, put the OP-Amp-circuit on a Veroboard and powered it from the USB-cable and finally put the whole pile into the box of an old WLAN-HUB. It looks ugly inside, but once I close the box I have a nice looking USB-connected generic 433MHz transmitter :-). 
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-{{ :​nexaremote4.jpg | Ready transmitter}} 
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-The circuit board to the right of the Veroboard is actually a receiver I tried to put in the same box. I had to give that up, since it is to sensitive to the electromagnetic noise from the USB. I had to use the [[modupm|UPM-recevier]] connected via a fem meter cable to get away from the noise. ​ 

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