1
\$\begingroup\$

I have a prototype board which has two RF modules on it, a 2.4GHz Wifi module (ESP-01) and a low cost 433.92MHz RF receiver module (Wenshing RWS-371F-6). My 433MHz transmitter (a remote control) sends data encoded in manchester to be decoded by the receiver, this part is working well. The data rate is 2000 bits per second and I am using 433.92MHz SAW ressonator on the remote control PCB prototype. I have a frequency meter, and its transmission frequency is exactly at 433.9MHz constantly. When the ESP-01 module is not connected to the board, I can control the relay of the board from 50 meters distance with short presses on the buttons of the remote control, and it almost always work at this distance (to control the relay). When the ESP-01 module is connected to the board, the 433MHz RF performance is very poor. For example, from only 5 meters distance I have to do a long press on the button in order to control the relay, and sometimes it does not work. And with the ESP module connected to the board, It does never work doing short presses on the button like works when the ESP-01 module is not connected on the board...

As can be seen on the photos, I have tested 433MHz module antenna with helicoidal and straight wire (17,3cm and 13cm), and with 13cm long wire the result is even worst.

This board have 12V (100KHz - LNK626DG) power supply that is generated from the mains, then the 12V is reduced to 5V (7805) and 3.3V (LM1117IMP-3.3), two linear voltage regulators. The board has a ground plane also, shared by all them.

The only thing connected to the 5V output is the 433MHz RF receiver. At the input of 5V regulator I have a 100nF ceramic, and at output 10uF ceramic 0805 16V, and at the two 5V supply pins of the 433MHz module I have a 100nF ceramic.

The ESP-01 is being supplied by a regulated 3.3V (this power supply will be changed by a buck converter of 1.5MHz on the next prototype). At the output of this regulator I have one 22uF ceramic, and very close the the 3.3V pin of the ESP module I have 2x 22uF 0805 10V ceramic capacitors.

In that board it is also possible to connect a bluetooth module like the HC-05 (bluetooth is also 2.4GHz) in place of ESP-01, and when the BT module is connected to the board and working, it does not cause interference on the 433MHz RF like the ESP module do, maybe due to the low-power RF of bluetooth.

I have noticed that the 3.3V output is at one edge of the PCB and the ESP connector is at the other edge of the PCB...

Do somebody know if is it possible in my board, to have a good performance on 433MHz RF and use the ESP module at the same time? Because in my board the ESP module seems to be causing interference on the 433MHz module's receiving capability.

Why is this interference occuring? And what could be done to solve?

Is it layout issue?

Datasheet of the 433MHz receiver module: www.web66.com.tw/_file/C3/31776/Dfile/1402897191832file.pdf?t=2019091807

Regards.

\$\endgroup\$
  • 1
    \$\begingroup\$ Have you checked whether the ESP module itself is working fine? Have you checked supply voltages, etc on the modules (ESP and 433MHz receiver) when this problem occurs? \$\endgroup\$ – Big6 Nov 28 '19 at 18:00
  • \$\begingroup\$ The ESP is working great, I have done a webserver with it, and its working fine. I have put the scope directly on VCC and GND pins of the 433MHz RF module and the signal is very good (straight line), and the 5V is good independently the ESP is attached of not to the board. The signal at 3.3V of ESP is also ok. The problem is persistent on the 433MHz receiver, and the result is simple to say, that is, if ESP is present, 433 is bad, if ESP is not present, 433 is good. \$\endgroup\$ – abomin3v3l Nov 28 '19 at 18:23
  • \$\begingroup\$ Those little 433Mhz modules are notoriously terrible, especially the receivers. Not saying that's your only problem but you should know that the little cheapo ones are pretty garbage. \$\endgroup\$ – Shadetheartist Nov 28 '19 at 20:53
  • \$\begingroup\$ Can you maybe share design files of your proto board (schematic, pcb) so that anyone can see what resources are shared between the ESP and the 433MHz module? \$\endgroup\$ – Cisco25 Nov 28 '19 at 20:58
  • \$\begingroup\$ Placing the PCB antenna next to the trafo isn't a great idea. From what I can tell, the magnetic field of the coil goes straight through the antenna... And of course that radio module alone is ASKing for problems. Turns out you get what you pay for. \$\endgroup\$ – Lundin Dec 2 '19 at 14:59
2
\$\begingroup\$

Your 433MHz receiver module has a trimmer in the rf coil and no crystal, which suggests it is a superregenerative type. These have poor selectivity and so are prone to interference at other frequencies. It also has no shielding, so a strong rf signal could 'break through' and be picked up by active components on the board. The ESP-01's antenna is less than 10mm away from the 433MHz antenna, so the opportunity for interference is high.

First thing I would do is rotate the ESP-01 180° or mount it vertically, so its antenna is further away from the 433MHz receiver. I would also consider using a higher-spec superheterodyne 433MHz receiver, oriented so its antenna is as far as possible from the ESP-01 and with shielding around it if not already shielded.

Your ground plane might be improved by moving it to the top of the board and routing more wires on bottom. That way it could act as shield preventing rf from the ESP-01 from getting into traces going to other parts of the circuit.

\$\endgroup\$
  • \$\begingroup\$ Do you mean something like this? I can buy a pair for tests... produto.mercadolivre.com.br/… \$\endgroup\$ – abomin3v3l Nov 28 '19 at 21:43
  • \$\begingroup\$ If I replace my "superregenerative" module by a "superheterodyne" (like the module of the link above), will I need to change the design of the remote control also? In order to work? \$\endgroup\$ – abomin3v3l Nov 28 '19 at 21:46
  • 1
    \$\begingroup\$ Yes, that module should work fine with your transmitter. \$\endgroup\$ – Bruce Abbott Nov 28 '19 at 21:57
  • \$\begingroup\$ This question may apply to this topic: Why superheterodyne is to be better than superregenerative? \$\endgroup\$ – abomin3v3l Nov 28 '19 at 23:16
1
\$\begingroup\$

As has been mentioned, regenerative receivers are notoriously terrible.

But even building something to receive OOK signals with a good sub--GHz data radio as Ti, SiLabs, etc sell, you still need to worry about local noise sources.

Decouple all power and signals between the radio and digital circuitry with low pass filters such as SMD ferrite beads. If you have a debug serial cable especially decouple that.

Avoid using a switching power supply, if you must start with one follow it up with a linear regulator.

These are not theoretical guesses, but rather issues found in actually building a device of this type.

Conversely, with a reasonable protocol it is not all that likely that the wifi radio will be transmitting while you try to receive, nor is that as likely (at least with a good sub GHz radio) to be an issue as one might guess.

\$\endgroup\$
  • \$\begingroup\$ I should have some SMD ferrite beads to make tests. In the case of this 433MHz receiver module, it has 8 pins, 3 pins are connected to GND, 2 pins are connected to 5V, 1 pin is antenna, 1 pin is the digital output, and the remaining pin is floating (it is a linear/analog output). Then your recommendation is to place a ferrite in series between the digital output and MCU, and in series with the 2 pins that are connected to the 5V rail? All these ferrites near the 433Mhz module pins? Ican try this tomorrow... Thanks for your help! \$\endgroup\$ – abomin3v3l Nov 29 '19 at 0:15
  • \$\begingroup\$ Between the 433Mhz module's digital output and the MCU input there is a 1K resistor because the module is powered with 5V and the MCU at 3.3V. Is an aditional ferrite required in this case? \$\endgroup\$ – abomin3v3l Nov 29 '19 at 1:13
1
\$\begingroup\$

In order to find root cause of interference, use the suggest methods given already to isolate Conducted noise with ferrite series chokes and Radiated clock noise with a dummy shield can over top to isolate coupling.

This could be a grounded "can" put over a protective insulator just to attenuate radiated EMI such as from harmonics of the 26MHz square wave clock. If it improves reception, then you know proximity and radiated EMI is the cause.

enter image description here

\$\endgroup\$
  • \$\begingroup\$ I did not understood what test(s) I need to do. Where do I have to add the ferrite bead? In series with the VCC signals of the 433 module? I did not understood about the dummy shield can and where it should be placed and also if it should be connected to GND. Could you explain more? Thanks for your help, but I have less knowlegde about RF. \$\endgroup\$ – abomin3v3l Nov 28 '19 at 23:12
  • \$\begingroup\$ Isolate the ESP-01 from causing interference. (1) cut +5V and add RF Choke across cut before Caps (2) turn on radiated EMI (stop the clock or block the radiated noise of the clock.) How to shield EMI? tiny Faraday cage in a can grounded over ESP-01 Or make an extension ribbon cable to move card away from 433MHz ccts. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 29 '19 at 1:20
  • \$\begingroup\$ I did some tests. I have placed ferrites in series on the 5V pins of the modules, before the capacitors, and also had a bad result with the 433MHz reception when the ESP module is connected to the board. \$\endgroup\$ – abomin3v3l Nov 29 '19 at 19:41
  • \$\begingroup\$ So I used an 8-way cable to make the ESP module about 15cm (~6 inches) farther from where it is normally mounted on the board. Result: 433MHz reception got bad too. \$\endgroup\$ – abomin3v3l Nov 29 '19 at 19:59
  • \$\begingroup\$ That implies proximity and radiated interference (shield it) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 29 '19 at 19:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.