HM-R 433 (FSK) sending junk characters

[Sharagim]

Hello,
I have a HM-R 433 (FSK) which is a FSK receiver module (plus a HM-T 433).
As I was not successful on making connection between two MC so I decide to check it with pc.
connect it to max232 but on terminal I am getting many junk characters (even when sender is off).
This circuit is on project board but I don't think noise make it like this (not sure).
I am using stable power supply but changing it was without effect too (going on battery ...) !!!
Is there any idea what is making it like this ?
BR,

 

[D.A.(Tony)Stewart]

use CM choke for noise and scope data. FSK is noisy when there is low signal. Check RSSI or AGC level on Rx module. Vdc on chip pin?

Or ensure Tx to Rx path is line of sight < 150m.

give details above if not.

 

[Sharagim]

Thanks for your reply.
I moved into a soldered board but I am getting same result.
This is a module which doesn't have any option for RSSI,... is there any way to find it when the module doesn't offer it ?
for V I am using a meanwell power supply 5v-dc .
the distance between to module is about 0.5 m (50cm) , but when the tx module is off I see many junk characters too.
could you please let me know what do you mean with cm choke , which kind and where to plug it ....

 

[D.A.(Tony)Stewart]

CM= common mode choke ... better write to their tech support
Is it an obsolete module?
**broken link removed**
I dont have your schematic, but similar one shows RSSI signal that indicates Rx Signal Strength Indicator,, DC proportional to Rx carrier level [-dBm] If signal is not adequate, Rx Data should be disabled in FSK, otherwise you get noise.

 

[Sharagim]

datasheet link : http://www.kosmodrom.com.ua/pdf/HM-R433.pdf
for better feeling I put some receving data here :

ȧT<STX>æ<BEL>ê<EOT>·Þ…?Æ<ÑlÏ«}á<BEL>ùRÀƒÑÛ…Ï<DC4>þ<ETX>ö´xb<ETB>úæ4À§ïœþÔl>à³9ø°ïbPP8*;úÉ T¥8<FF><DC4>o<SO>XåwP½<ETX>Ô†?*<EOT>o9¾‰X¸dp=ø<RS>ó
n<SI>B<VT>Ï<ACK>†r†àq¿üÓ2K¤<ACK>Þ>ù<ACK>þõŸ³ü~þ’Í<BS>ð<LF><DC3>ƒÂ5HøÉ

 

[D.A.(Tony)Stewart]

You need to scope all the internal pins and see what is going on. to see if it is defective or working ok.. Use spectrum analyzer with scope probe to sniff LO etc.... Look at better options **broken link removed**

 

[vinoth8051]

Hi,
Better you may go with very basic steps to ensure every thing, other than RF module is alright.
1) Establish wired RS 232 communication between Microcontroller and PC with some typical baud rate such as 4800. (-> if this works, atleast we are sure that no error in implementing RS232 protocol)
2) Now interface FSK receiver to PC ( with proper voltage level conversion e.g with MAX 232 ) and FSK transmitter to Microcontroller. (let battery be your power source for TX side)
3) Try to send single constant character such as "A" continuously.
sending a single character continuously would help us to easily distinguish between junk values and baud rate or flow control problems.

 

[Sharagim]

Hi,
Thanks for your comments.
Finally I got data on receiver , bt it is not 100% accurate .
for example :
the correct data should be :

***<start>@#@#@23.50@#@#@</start>*******

But sometimes I am getting :

%%%%šÑ…ÉÑù@#@#@23.50@#@#@</start>*******

or

RRRâšÑ…ÉÑù@#@#@23.50@#@#@</start>*******

Is there any idea why it is working like this ?
I tried with battery too and nothing changed.
MC send data in there parts,
first send some "*" then some data and again some "*" .
This problem happening in first "*" parts. last part * is always ok .

BR,