RF Receiver 315MHz interference by RC Helicopter.

[Innovative]

I just bought a RF Receiver 315MHz for my FYP to control the RC Helicopter. When the helicopter is stop or run on slow RPM, the RF receiver working well. However, when increase until around 300RPM, the RF Receiver was not able to received signal from the transmitter. Do you have any circuitry to reduce the interference from RC motor to 315MHz receiver?

[yonghui]

hi,

how u connect it now?
the interface is between microcontroller?


regards,
yh

[Innovative]

What you means how i connect it? The data of RF 315MHz receiver is connect to RB2(RX) of the PIC and output of the PIC control the PWM of motor. The circuit board of receiver was mounted on the Helicopter body and connect by 7.4V-->7805-->5V. The problem is on Transmitter to REceiver. Means when the Helicopter is stop or run on slow RPM, it can receive the signal well for increase, decrease, stop... etc. (I am using UART protocol, so what i sent it can be recerived and shown on LCD,. There are no doubt on the TX->RX without turning of Helicopter.) While the speed of blades increase until certain level, it is unable to receive any signal from the Transmitter RF Transmitter 315MHz (RF-TX-315). Please advice!

[ABSF]

The data of RF 315MHz receiver is connect to RB2(RX) of the PIC and output of the PIC control the PWM of motor. The circuit board of receiver was mounted on the Helicopter body and connect by 7.4V-->7805-->5V.

The problem is on Transmitter to REceiver. Means when the Helicopter is stop or run on slow RPM, it can receive the signal well for increase, decrease, stop... etc. (I am using UART protocol, so what i sent it can be recerived and shown on LCD,. There are no doubt on the TX->RX without turning of Helicopter.) While the speed of blades increase until certain level, it is unable to receive any signal from the Transmitter RF Transmitter 315MHz (RF-TX-315). Please advice!

Is your motor inside the heli also use the same battery used by the PIC?
How's the connection between the PIC pwm to motor? Through a transistor or MOSFET?
Is your TX also controlled by another PIC?

You'll need to filter the supply lines properly using capacitors and inductors especially the +5V lines. The interference is probably comming from the motor interfering the PIC or RF Rx. You have to determine where. Then screen the motor or PIC with metal casing and see if it works.

If you suspect the TX to Rx is cauing the problem. Then get a better (more powerful) TX and RX pair to replace your cheap ones and see if they work.

Allen

[Innovative]

Yes, the RX module, PIC and motor is using same battery and motor controlled by MOSFET. TX using another PIC with different battery/USB 5V power.

Do you means using the inductor and capacitor on the RF RX and PIC +5V power? What is the value i should use and how is the connection? How can i determeine where is the interference if i do not have oscilloscope at home?
BTW, if i screen the RF RX module with metal casing is it still able to receive signal from TX?

What is the better (more powerful) TX and RX pair you advised? For the original RC Helicopter control circuitry also a cheap China brand but it able to control well without interferrence.

[ABSF]

What I mentioned above are just proposals. Without using test equipments to determine where the motor is interfering your circuit. I can only guess and suggest preventions.

How's your circuit constructed? On breadboard, stripboard or etched your own PCB? Did you put 100nF caps across the motor? I am guessing the noise generated by your motor is interfering with the data that enters your PIC after stripping off from the carrier. So you can either concentrate on reducing the noise of your motor or reduce the interference of you RF devices by screen.

No, screening will not shut out the RF device from transmitting or receiving. I remember there is a point where you can connect a wire to act as a arial for your Tx or Rx. Read your RF module's datasheet again.

Allen

[Innovative]

Gratly appreciated for your advice, it is really helpful and i will test it out by today and let you know what is the outcome.

I have tested on the breadboard for the receiver and the bread is far away from the helicopter, it face same issue as well. Then, i etched the PCB and put inside the helicopter, it is more worst. Do you have any preference for the layout need to take care? Opps, i not put any 100nF on the motor, does this help to reduce the noise from motor?

Yes, i have connected the wire act as attenna of the RX and TX. This is my question if i just screen the module and let the wire expose outside, does the wire will coupling by the EMI noise as well to interrupt the signals?

Thank you very much!!

-CK-