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I've bought a Realtek RTL2832 DBV for my RPI to read 433 mhz data and a transmitter HM-T433. I can successfully receive messages from two 433mhz remotes with the rtl_433 utility, but when I try to send any data I am always getting readings like

[00] {0} 00 : 00000000

I've tried sending the data trough the ninjablock utility, RCSwitch, pilight, custom code and a lot more of other possibilities but all readings from rtl_433 are bits of 0.

Is this normal? Is there something wrong with the transmitter (how can I check that)? Am I not reading the data correctly?

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  • piscope will show you data being sent and received.
    – joan
    Mar 22, 2015 at 12:12
  • What antenna are you using with the HM-T433?
    – scruss
    Mar 22, 2015 at 12:32
  • I have a 10cm wired soldered to the transmitter. The RTL2832 DBV receiver is near the transmitter, I've tried from 2cm distance to 1m and still the same.
    – Ali Cornea
    Mar 23, 2015 at 15:09

2 Answers 2

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I think you are mixing up signal moldulations.

HM-T433 uses FSK (Fequency Shift Keying).

Most applications in 443MHz use ASK (Amplitude Shift Keying) and of those most use OOK (On/Off Keying). That means they either send a signal with constant amplitude and frequency for "1" and don't send anything at all for 0.

RTL2832 is capable of doing both FSK and ASK. But you have to configure it correctly for your application. The rtl_433 utility is fitted for ASK/OOK so your transmitter does not match. You will need to find another utility that uses FSK.

Try GQRX to find out if you receive the signal at all.

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This site says that HM-T433 is a perfect match for HM-R433. The other one is most likely a just a demodulator/TV tuner. Do you have receive modules?

EDIT: TRY FLIPPING THE TX/RX PINS

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  • I have only the HM-T433. The thing is that with another transmitter (cheap Chinese one) all is working fine.
    – Ali Cornea
    Mar 23, 2015 at 15:11
  • Why not use that?
    – Aloha
    Mar 24, 2015 at 8:30
  • That's not mine :) I've borrowed from a friend of mine.
    – Ali Cornea
    Mar 25, 2015 at 11:21
  • @AliCornea Then buy one yourself, since it's a cheap one. Mar 31, 2017 at 7:40

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