Are you sure that your module works well to 12V12 V?
Since heit is the "XY-MK-5V" model I think heit has the voltage up to 5V5 V as ideal.
For all I know, these modules work well between 3.3 V and 5V5 V, maybe saturating the circuit.
Really, the transmitter work with up 12Vto 12 V.
But I suspect that it does not work at the frequency in question see there's. See, there are a lot of bad information on the internetInternet about them.
- Product Model: MX-FS-03V
- Launch distance :20 20-200 meters (different voltage, different results)
- Operating voltage :3 3.5-12V12 V
- Dimensions: 19 * 19mm19 mm
- Operating mode: AM
- Transfer rate: 4KB 4 KB/ Ss
- Transmitting power: 10mW10 mW
- Transmitting frequency: 315Mhz315 MHz
- An external antenna: 25cm25 cm ordinary multi-core or single-core line
- Product Model: MX-05V
- Operating voltage: DC5V
- Quiescent Current: 4mA4 mA
- Receiving frequency:315Mhz315 MHz
- Receiver sensitivity:-105DB105 dB
See more at: http://www.buildcircuit.com/how-to-use-rf-module-with-arduino/#sthash.u2AxOcew.dpufHow to use 315 MHz RF transmitter and receiver modules with an Arduino