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I am stuck on a problem with RF Module. I am trying to make an RC Car and facing a lot of problems while doing so.

I am using a 433 Mhz RF module, HT12E-D encoder decoder, L293D and 2 BO motors(DC). My circuit works fine with 100-200 RPM Motor but as soon as I use a faster motor such as a 300 RPM motor the circuit stops receiving any signal due to which the car just moves according to the last signal.

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As soon as the high RPM Motor is connected following happens:

  • The transmission board stops working(when any other button is pressed no response is there)
  • The data pin LED continuously blinks
  • Have to stop the motor forcefully to continue transmission

The best guess would be the motor driver circuit is taking up all the current. so I tried two different power sources for the circuit I powered up the Motor Driver circuit using 7.4V li-ion Battery and the receiving part with a regular 9V battery. but still the same problem is there. I am thinking of using another Encoder decoder IC P2272 or HC148. Any suggestions? Please help

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  • \$\begingroup\$ You have no decoupling capacitors at U1 or IC2. Wouldn't that be a problem? \$\endgroup\$
    – Transistor
    Jun 28, 2018 at 18:44
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    \$\begingroup\$ Is this your 1st EMI problem? The radio needs clean voltage and low radiated noise \$\endgroup\$
    – Tony Stewart EE75
    Jun 28, 2018 at 18:44
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    \$\begingroup\$ While the specifics can vary, much of your problem stems from poor part choices. 433 MHz radios are typically quite crude, and (at least with conventional modulations) basically never used for RC vehicles; they went straight from HF/VHF to 2.4 GHz packetized data radios like the nRF24 series. Also the horribly lossy L293D is not what you want for driving DC motors on battery power; you want an FET bridge or at larger sizes discrete FETs. \$\endgroup\$
    – Chris Stratton
    Jun 28, 2018 at 19:39
  • \$\begingroup\$ I tried the same thing with a better version of motor driver TB6612FNG but the same problem persists thus now trying the approach of using 4 relays to drive 2 DC motors. What do you suggest? \$\endgroup\$
    – Arduino
    Jun 29, 2018 at 21:27
  • \$\begingroup\$ I'm voting to close this question as off-topic because it has been abandoned by the asker in a form where it is hard to tell what is being asked. It is particularly mysterious how connecting a motor causes "the transmission board" to stop working. \$\endgroup\$
    – Chris Stratton
    Sep 3, 2018 at 18:14

2 Answers 2

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To reduce EMI Problems I recommend:

  • place 100nF X7R Ceramic capacitors directly at U1 pin 18 and IC2 pin 16.

  • add some µF X7R ceramic capacitor at IC1 pin 1 and 3. (2,2µF up to 10µF)

  • C1 is not intended to be "used" by IC1. It shall store the energy required by the Motor. Move C1 close to IC2 Pin 8.

  • Add some µF ceramic capacitor to IC2 Pin 8.

  • Add some nF ceramic capacitors between: 1y-2y, 4y-3y, 1y-GND, 2y-GND, 3y-GND and 4y-GND to filter the brush noise. The values need to be tried.

  • choose ceramic capacitors which have Umax dubble the voltage of your Max voltage.

  • Layout: use one solid ground layer without a single trace. other
    Layers: Separate the traces with switching noise from the antenna &
    connector part

by this the EMI is not spreaded that much by the Motor and IC2 and the EMI imunity of U1 is improved

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Look at some commercial RC cars, and you'll often find a tiny ceramic capacitor connected across the terminals of each DC motor. Motor-brushes create large voltage-impulses during each commutator break. "Commutator noise." Such mechanical pulses can be like a Marconi transmitter: kilowatts for nanoseconds, heavy in UHF/microwave emission.

One solution is to use FM modulation, spread-spectrum, etc., noise-immune channels. A simpler solution is to add a short-lead ceramic capacitor, 0.01uF or larger value, connected directly across each motor terminals. (If connected elsewhere, such as onboard PCBs, the motor wiring may turn into UHF antennas.)

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