ASK 433mhz interface with microcontroller

[Darpan747]

Hello,
I am making a pc controlled application where I have used max 232.
So through uart , i send characters.
and i have connected ask transmitter to max232 tx pin.
and receiver on the rxd pin of microcontroller.
but these is not working.
I have tested the modules in other application, they are perfect.
and using wired connection that means directly connecting tx pin of max232 to rxd pin of uc, the code also works.
can someone please help me on this.:?::-(

 

[betwixt]

It isn't clear what you are doing. Please draw a block diagram of the system, it sounds like you are using the MAX232 to interface the PC and microcontroller to the ASK tranmitter/receiver. The levels it needs are probably not RS232 and if you are using the same MAX232 in both directions it implies you have a direct ground connection between each end anyway.

Brian.

 

[Darpan747]

Hello,I have attached a rough block diagram.
I hope that you get the idea what i want to tell.
my pc sends the signal through uart, and i have connected ask tx to it.
and ask receiver is connected to my controller.

 

[betwixt]

That should work OK although be aware that you may have to encode and decode the data to get it through reliably.

You need to split the problem into two halves, first find out it you are transmitting anything at all. Possibly the PC serial port is not sending unless it has it's handshaking lines set correctly. An oscilloscope is the best test instrument for this but if you do not have one, wire an LED and 470 Ohm resistor in series and connect them across the data line to the transmitter and ground. It may light up or it may not but when data is being sent it should flicker.

If you do seem to be sending data to the transmitter, move the LED to the output of the receiver and try there. Again, it should flicker as data is being sent. If it does flicker the problem is in the MCU hardware or software, if it doesn't the problem is in the receiver. Be aware that these receiver modules tend to produce random output when nothing is transmitting to them so be careful that it really is your transmission you see and not interference from elsewhere.

Brian.

 

[ANS HAFEEZ]

my last smster project is same as you are doing i tried so hard and also achieve trnsmission over 433Mhz but there is TOO MUCH NOISE TO WORK perfectly..

FIRST YOU have to send data in micro and then transmitt it
and better is to use some encoder/decoder IC pair between micros i have used TX2B/RX2B pair which provides you almost 10 channels other options is to implement menchestor coding to remove noise which is very complex for me THANKX ....

 

[Darpan747]

Hello Brian,
Hello,
I have tested these ask transmission using encoders and decoders.
I had used ht12e and h12d.
using that , the project was working very fine.
But I want to make my project work without encoder and decoders.
I also tried using that led method.
the led blinks when i send something from UART, but on the receiver side the led does not blink, these i tried using 2 ask receivers.
Suggest.
Hello Hafeez, i have tried with encoder and decoder, and they are working fine, can you suggest me without encoder and decoder.
Thanks

 

[betwixt]

I don't think it will ever work without some sort of signal conditioning. The encoding isn't to encrypt the signal, it's needed to make it more obvious to the receiver. What goes wrong is this:

1. With no transmission the receiver produces random output which at times will look like data and may cause the receiver UART to prematurely start to 'frame' some data.
2. When the transmission starts it takes a few mS for the receiver to adapt to the new signal level, this means you can lose the start of every byte that has a pause before it.

The minimum solution to these is to send a 'preamble' before the data, for example to send several bytes of 0xAA before the data you want. They do two things, firstly they keep the tranmission alive for a short period so the receiver has time to adapt to it and secondly they give the receiving UART something to align the data frame to. By that I mean time to find the start and stop bits. You ignore the 0xAA (or whatever value you choose) at the receiver so the next valid byte it sees is the one carrying your data.

Brian.