0
\$\begingroup\$

Following the recommendations I got on my last question about troubleshooting communications in my RC car, I probed the +5V power pin of my RF 434MHz receiver module with my oscilloscope. Below is a snapshot of it.

Scope shot of receiver Vcc pin

The periods marked in red (1 & 2) are the exact moments the receiver lost connection with the transmitter. Period 1 happen right after I applied full throttle (when the voltage raised) and then let it come to a full stop. Right after that, the voltage drops and the receiver output pin goes silent (LOW) during half second. On period 2, the car is sitting still and the voltage drops spontaneously below 5V and the receiver looses connection again.

So, it's clear to me that the receiver power supply is noisy. It's varying around 100mV when the car is stopped and shows up to 200mV pp. The receiver doesn't seem to like when the voltage drops below 5.0V.

My question is: how can I make the power supply more stable for the receiver module?

I can think of two solutions:

  1. Add a filter to the receiver +5V pin. If so, what filter circuit should I use?

  2. Add a buck/boost voltage regulator to feed the receiver. Would this remove the ripple on the supply?

\$\endgroup\$
1
\$\begingroup\$

If your receiver shares the power supply with the motor, then it's going to drop at full power. You could filter momentary burst of full power... but the longer the on time the harder it gets. A separate power source would work.

Regarding the receiver module, if it's that sensitive to the input power, then maybe add another battery and a three terminal voltage regulator.

\$\endgroup\$
  • \$\begingroup\$ They used to share the power supply, then I had more problems (the MCU would boot upon reaching full power). Then I separated both supplies but they still share the negative (ground) connection. That is, the MCU and receiver have a separate set of 4x NiMH rechargeable AA cells. The motors have a separate 6-cell NiMH AA pack. But even on separated supplies, the motors seem to be pulling the receiver supply up and down. Thus my request for help. \$\endgroup\$ – Ricardo Sep 9 '14 at 0:51
  • 1
    \$\begingroup\$ Hmm, that's weird. Are you sure it's a power supply problem? You talk about lot's of noise. Maybe more filtering or shielding, or both. \$\endgroup\$ – George Herold Sep 9 '14 at 1:10
  • \$\begingroup\$ The scope shot above is from the receiver power supply pin. According to the datasheet (available on the linked question) it's supply should be 5 +/- 0.1V. And the connection drops exactly when the supply voltage drops a little, in the marked regions. But the supply is noisy, too. So, yes, I've got both problems. My question actually, what filter should I apply to my receiver? The full schematics are also in the linked question. \$\endgroup\$ – Ricardo Sep 9 '14 at 1:38
  • 1
    \$\begingroup\$ Hi @Ricardo, sorry I couldn't get the link to the receiver to work. If it's that sensitive to the input power, then maybe add another battery and a three terminal voltage regulator. \$\endgroup\$ – George Herold Sep 9 '14 at 12:35
  • \$\begingroup\$ Yes, that's where I'm getting at. Thanks for your help!! \$\endgroup\$ – Ricardo Sep 9 '14 at 12:50

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.