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Laipac RF Transmitter/Receiver

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rewguy

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I need help with TLP / RLP from Laipac! PDF can be found here:

https://www.electro-tech-online.com/custompdfs/2004/03/TLPRLP434.pdf

I am working on implementing a 315MHz transmitter/receiver with a microchip 12f629 on the transmitting end and a 16f84a on the receiving end. When I read the PDF above that describes the transmitting/receiving modules, I was left with many questions.

Basically, how do these things work? Let me explain. When I put +voltage on the transmitter, does the digital data out pin of the receiver go high? Isn't that the point? I thought it would be simple to test this by making a LED 4x7 display on the receiving end say "----" when the pin was low and "SGnL" when it was high. Then I made the transmitting end simply put positive voltage on the data-in pin and take it off, sort of like blinking a LED, only blinking the positive voltage on the transmitting pin about every second or so.

Well, the problem is this: If the transmitter is off, the receiver will show SGnL for about a second, and then it will light up both SGnL and ---- at the same time (jumping back and forth so quickly that they both appear lit). This is very strange, as I would expect the pin to be low if there is no transmitter.

Hooking up the tranmitter, it appears that the correct result is show on the display only for maybe a tenth of a second after the transistion. After that, both ---- and SGnL appear. This leads me to believe that if nothing is being transmitted, the pin somehow oscillated back adn forth between 0 and 1, and during transition, it is 0 or 1 for a tenth of a second.

What is the deal with this? How am I supposed to transmit data and then read it? Does this have anything to do with TTL input and ST (Schmidt trigger) input? What is the difference?

Also, all diagrams I see with this device are using HT12E to transmit and HT12D to receive. Should I be using these, and what do they do? What is the advange? Please help.

rewguy
 

Jerran

New Member
I just started playing around with RF communications myself. I dont have a lot of knowledge in the area but Ill pass on what little Ive discovered till a more knowledgable poster shows up :)

Im using a different transmitter/reciever module but am using the same encoder/decoder as you listed. From my experience this is how they both function.

Encoder:
The encoder takes parellel data from the 4 pins(d0 - d3) and turns it into a serial data stream to the transmitters output. The encoder has a transmit enable pin that must be pulled to ground before any data is sent. Once the transmit enable is grounded data is sent until its brought back to V+ or left floating, the decoder will latch d0-d3 to what ever state the pins on the encoder where set at when the transmit enable pin is brought back to V+.

Decoder:
The decoder takes the serial RF data and sends it out parellel on pins D0-D3. This data is latched when the encoders transmit enable pin is brought back to V+.

Using encoders/decoders ensures the data being sent is valid, the circuit wont be affected by stray radio waves of the same frequency. They are also easily manipulated threw the output of a microcontroller.
 

Jess--

New Member
I know this is an old thread but I will post my knowledge of transmitters / receivers.

if you leave one of these receiver modules on while there is no signal being transmitted then it will start receiving static, most (if not all) of these receivers have an amplifier on board which takes a signal (no matter how small) and turns it into full 0 - 5v data which is great for digital data that is encoded, but if you are looking for just signal present or not present its pretty useless.

most decoder chip designs (ht12D etc) will only activate after receiving the correct code three times within a specific time (depends on the speed you are running the chips) this very efficiently ignores static.
 
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