How to reduce motor electrical noise?

Question

I have made RC car using using ht12e and ht12d, two geared DC motors, RF module. Now my problem is that when motor starts rotating, it is generating some kind of RF signals which are interfering with my RF receiver signals and it cannot receiver further signals from the transmitter unless I reset power to it. I read about low pass filter over net but couldn't understand well.

I tried shielding motors using aluminium foil which helped to some extent but not completely. How can I eliminate this problem using simple components?

This is my circuit:

I have used 433 MHz ASK module.

Answer 1

Firstly look how I've modified the power and ground leads below (in red): -

It's important to star-point different circuit blocks back to their respective batteries in order to minimize loop current emissions. The important one is the 12V local to the L293D chip. Talkingof which, be sure to use the version with a "D" on the end because that has internal flyback diodes and without these you'll be producing voltage spikes that could interfere with tesla coils (that was a joke that last bit).

Next are decoupling capacitors across each motor - If you are using PWM control you need to be a bit cautious with high values as these will suck energy from the pulse width modulation. Try 10nF across each motor and if necessary try a 10uH inductor in series with each motor with a bigger cap (like 100nF) still directly across the motor.

The problem could be also solved by making the whole of the 0V system a local earth plane - there may still be currents flowing in your current set-up that cause the HT12D to glitch and lose control.

Make sure you have all the major electronic components decoupled with caps too. Maybe 10uF and 10nF across the HT12 and L293D and receiver. HT12 and receiver should be close together and have as a minimum a shared local earth plane.

Answer 2

Measure with oscilloscope the VCC of the module, and VDD of the HT12D, and check for any electrical noise. If so, you may need to add decoupling capacitors (e.g. 0.1uF) to the 5V near these devices.

While still measuring, try various low value capacitors placed across the motor terminals. Start with a few picofarad and double each time.

Answer 3

The answer of @JamesCameron is good, but I'd separate the power path to the RF parts and the motor parts as much as possible with LC filtering:

• there should be a clear point, where the power goes off to the RF receiver and the motor driver
• from that point, add chokes (actually even ferrite beads might help) in series of both circuits - reducing the high freq. kickbacks from the power lines.
• after the choke, add smoothing electrolytic capacitors in parallel with the circuits (220uF will most likely do, or might even be overkill.)
• also, immediately at the power, and "non-RF" pins of the sensitive device add very small (~0.1pF) capacitors to reduce RF noise picked up through those pins.

I'd also shield the whole motor driver board in small metal box, and put it as far as it is possible away from the receiver.

Answer 4

You should look into replacing the RF module. I say this because ASK is particularly vulnerable to noise because noise is very additive and can quickly degrade amplitude modulation schemes. Its the reason why AM radios can hear lightning and other things that are going on. Using FSK or similar will help increase your noise immunity. I say this because reducing motor noise comes down to isolating from it.

Take a look at XBee or similar simple to use modules. If they use FSK or DSSS you will save yourself a lot of headache.