Trouble with RF module (ASK 434Mhz)

Thread Starter

allahjane

Joined Sep 19, 2012
75
Hello,
Hey I got this RF transmitter and receiver pair from ebay (Says 434Mhz and ASK modulation)

http://www.ebay.in/itm/280952855034...:IT&_trksid=p3984.m1439.l2649#ht_1883wt_1139

Its same as

https://www.sparkfun.com/products/8950

I prepared a test circuit on a Breadboard/project board as shown in the Attached Image



on turning on the power the Data Pin on the receiver side Always remains HIGH (+5v) no matter what

Even when the transmitter is removed from the circuit the receiver give HIGH output at data pin

I'm using the digital data pin and the ground pin to form the data out circuit as you can see in the figure labeld as data terminals

However a the data pin on receiver goes to LOW state for a split second whenever i give a +5v to the data pin of the transmitter i.e closing the D switch (this may be due to the fact that I'm using the same power Source for both transmitter & Receiver) after then it quickly becomes HIGH again

there is no tuning controls available on the pair either

What am i doing wrong? has the ASK modulation has to do something?


Please help me
 
Last edited:

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
These module can't be used without any uC or Decoder chip like HT12E/D if u want to test u have to use Oscilloscope, testing with LED at Data o/p will tell nothing....
 

ErnieM

Joined Apr 24, 2011
8,377
Looking at the Running TX433 and RX433 RF modules with AVR microcontrollers app from Sparkfun there is a image of a transmitter and receiver "In the last pictures you can see data packets of 4 bytes seen on the oscilloscopes. Yellow signal is from transmission data line(TX) while blue is taken from receiver data line(RX):"




So it seems the receiver data is normally high for no data.

He's got some good comments on how these things work in the real world well worth reading. You do need to transmit real serial data to receive the same, though a simple square wave may go thru the pair as well for a test application.
 

Thread Starter

allahjane

Joined Sep 19, 2012
75
THANKS I got it Actually the receiver is highly susceptible to noise in absence of transmission from the transmitter...

as the author says..
when transmitter doesn't transmit any data – receiver catches various noises that come from power supply or other sources because receiver likes adjust its input gain depending on input signal level
 

Thread Starter

allahjane

Joined Sep 19, 2012
75
THANKS I got it Actually the receiver is highly susceptible to noise in absence of transmission from the transmitter...

as the author says..
when transmitter doesn't transmit any data – receiver catches various noises that come from power supply or other sources because receiver likes adjust its input gain depending on input signal level
 

THE_RB

Joined Feb 11, 2008
5,438
I've seen these on ebay lately for $3.95 for a PAIR (one TX and one RX).

They can have issues from the receiver cranking up gain when sending serial high bytes like 0xFF, it's better to use manchester encoding or some encoding type that tries to keep roughly the same amount of 0 and 1 bits over time.

If you must use serial you can send it in half bytes (send two serial bytes, each is half 0 bits and the nibble you are sending). Or you can send a preamble byte like 0x55 so the receiver can set the gain before the data byte(s).
 
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