Driving DFPlayer Mini from an RC receiver

Support
1

I have a four channel radio control receiver in a model. Channel four is an on/off servo channel. I am trying use it to trigger a soundtrack to play on the DFPlayer Mini. I know that I can do so using a Pololu RC switch with digital output between the servo and the DFPlayer but am trying to avoid the cost and complexity. Is there any way of a connecting them directly please?

2

Hi @Peter197296

Welcome to the forum!

Since your RC receiver outputs a PWM signal for the servo, and the DFPlayer Mini in standalone mode just needs a pin pulled low to play the next file, you can create a super simple interface using a low-pass filter and a transistor.

For that you’d need:

You would wire it up in a similar fashion to below:

RC CH4 (PWM)
|
10kΩ
|
±—> to transistor base (via 1kΩ)
|
1”F
|
GND

Transistor:

  • Base: from above
  • Collector: DFPlayer IO1
  • Emitter: GND
3

‘on/off servo channel’ is typically used to describe a channel in the transmitter, not the receiver, and means that the channel is a signal for the servo that is either on or off - that is, it is either sending PWM at zero value or at full value depending on a two-way switch. That’s not suitable for driving the player attached to the receiver without a PWM decoder, such as the Polulu device you mention.

Using that term for a receiver seems inconsistent - it would be either an on/off channel (which would work as a switch) or a servo channel. Do you have a reference for that receiver with a description of how that channel works?

4

Thanks Dan. I will give that a go.

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5

Dan,

I tried your suggestion but got nothing. The PWM voltage from CH4 to ground is 0.32 when the channel 4 button is pressed and 0.17 when released. However I get no volts at all at the transistor base at any time. Does that give you any clues please?

Regards

Peter

6

Hi Dan
Don’t think that is going to work.
If the signal is a servo drive it will be a pulse of between 1mSec and 2mSec with a period of 20mSec.
So that will be only a 10% duty cycle at best.
Your filter will produce a DC voltage of the AVERAGE PWM signal which if a 3.3V peak will be 0.33V at the filter output which is about what Peter is seeing.
Now to even look like turning the transistor on will require at least 0.6V at the base. Why Peter is seeing nothing I don’t know but there is not much hope of turning a transistor on with that set up. Even with a 5V system you would only achieve 0.5V which is still not enough.
Cheers Bob

7

Hi @Peter197296,

Appreciate your persistence here, and totally understand wanting to keep things simple and inexpensive. That said, based on what you’ve tried and the PWM signal limitations, it’s looking increasingly unlikely that a purely passive or DIY solution will be reliable.

You could go down the microcontroller route (something like a Raspberry Pi Pico or Attiny is only around $5–10 AUD), but once you factor in setup, programming, and possibly needing USB adapters or extra components, it can quickly become just as involved, if not more, than using something like the Pololu RC Switch.

So while it might seem like the more “expensive and complex” option up front, in practice, the Pololu switch is actually the cleanest, most plug-and-play solution for this sort of RC-to-logic signal conversion. No soldering filters, no writing code, it just works, reliably.

Might be worth saving yourself the time and hassle in the long run!

1 Like
8

Ryan,

Yes, I am rapidly coming to the same conclusion. Thanks to all for your help.

Regards

Peter

1 Like