DFPlayer Mini with RF Transmitter
Account cancelled 2017-10-24 14:26:05 2417 Views0 Replies Hi,
I am having some problems getting DFPlayer to work with my project which also uses a small 1W VHF FM Transmitter.
My Project is an Amateur Radio Repeater and Logic Board.
Basically, it takes a radio signal coming in on one frequency and repeats it out on another frequency and I've used a DFPlayer Module to store and play audio tracks containing Morse Identification and Voice Beacon Announcements which are played and transmitted every 15 minutes to identify the repeater.
But I'm having big problems getting the DF player to play nice with the Transmitter.
At first, when the transmitter was transmitting, I'd get no audio at all on the carrier, until I touched or went near the metal box the project is housed in and then the audio came up and I could hear the audio. I got round this by using a 47uF Electrolytic in series with the Speaker Output from the DFPlayer Module to the MIC IN on the Transmitter.
However, doing this cleared that problem up but brought on that 250Hz humming which is clearly audible.
I've tried all sorts from De-coupling everywhere on my circuit to trying to add High Pass RC Filters in the audio line to null out that humming at that frequency but nothing works and any RC filter I try just kills the audio completely.
One other problem I had with my circuit was using the SPKR output to feed into my MIC IN on my transmitter...
I am using the SPKR+ wire with the above mentioned 47uF Cap in series for DC blocking and that works, I hear audio - with that humming so I thought maybe connect the SPKR - to GND but that just wiped out the audio completely again. So at the minute, SPKR - is free floating and I'm just using the signal from SPKR+
I've been working on this problem for weeks now and I'm now running out of ideas. Nothing I do gets rid of this 250Hz humming on the audio line coming from the DFPlayer. I even tried re sampling the MP3s and using a variety of Sample Rates and Bit Rates in case it was that but that didn't help either. The humming remains.
I have the following connections on my DF Player...
VCC goes to 4V which is switched "On" by my MCU via a P-Channel Mosfet. VCC is decoupled at both ends (Where it comes into the PCB and at the DFPlayer).
GND goes to a common Ground Plane shared by everything on the PCB
RX Goes to my MCU Via a 1K resistor (my MCU is running at 3.3V but I still needed the resistor due to some strange paracitic stuff going on through my circuit across the RX Line).
TX is NOT Connected and is free floating.
SPKR + is connected with a 47uF Capacitor in Series to MIC In on my Transmitter
SPKR - is Free Floating because it doesn't like connecting
Also one very strange thing I've noticed when I put my Oscilloscope on the audio line and that's during playback, I can see serial square wave data flashing up on the trace every now and then like it's picking it up from somewhere... However, during playback from the MP3 there should be no serial data being sent or received in my program so I don't know why that's happening either.
Any help would be appreciated, I'm getting desperate at this stage. I am so close to completion and everything is working except for this horrible humming.
I've even used screened power cables with the screen connected to GND and the metal enclosure, I've laid foil between the lid of the box and the antenna for extra screening, I've tried numerous values of decoupling capacitors at various points on the board, I've tried RC Filters.. nothing I've tried gives me nice clean audio at a reasonable level.
All ideas welcomed!
I am having some problems getting DFPlayer to work with my project which also uses a small 1W VHF FM Transmitter.
My Project is an Amateur Radio Repeater and Logic Board.
Basically, it takes a radio signal coming in on one frequency and repeats it out on another frequency and I've used a DFPlayer Module to store and play audio tracks containing Morse Identification and Voice Beacon Announcements which are played and transmitted every 15 minutes to identify the repeater.
But I'm having big problems getting the DF player to play nice with the Transmitter.
At first, when the transmitter was transmitting, I'd get no audio at all on the carrier, until I touched or went near the metal box the project is housed in and then the audio came up and I could hear the audio. I got round this by using a 47uF Electrolytic in series with the Speaker Output from the DFPlayer Module to the MIC IN on the Transmitter.
However, doing this cleared that problem up but brought on that 250Hz humming which is clearly audible.
I've tried all sorts from De-coupling everywhere on my circuit to trying to add High Pass RC Filters in the audio line to null out that humming at that frequency but nothing works and any RC filter I try just kills the audio completely.
One other problem I had with my circuit was using the SPKR output to feed into my MIC IN on my transmitter...
I am using the SPKR+ wire with the above mentioned 47uF Cap in series for DC blocking and that works, I hear audio - with that humming so I thought maybe connect the SPKR - to GND but that just wiped out the audio completely again. So at the minute, SPKR - is free floating and I'm just using the signal from SPKR+
I've been working on this problem for weeks now and I'm now running out of ideas. Nothing I do gets rid of this 250Hz humming on the audio line coming from the DFPlayer. I even tried re sampling the MP3s and using a variety of Sample Rates and Bit Rates in case it was that but that didn't help either. The humming remains.
I have the following connections on my DF Player...
VCC goes to 4V which is switched "On" by my MCU via a P-Channel Mosfet. VCC is decoupled at both ends (Where it comes into the PCB and at the DFPlayer).
GND goes to a common Ground Plane shared by everything on the PCB
RX Goes to my MCU Via a 1K resistor (my MCU is running at 3.3V but I still needed the resistor due to some strange paracitic stuff going on through my circuit across the RX Line).
TX is NOT Connected and is free floating.
SPKR + is connected with a 47uF Capacitor in Series to MIC In on my Transmitter
SPKR - is Free Floating because it doesn't like connecting
Also one very strange thing I've noticed when I put my Oscilloscope on the audio line and that's during playback, I can see serial square wave data flashing up on the trace every now and then like it's picking it up from somewhere... However, during playback from the MP3 there should be no serial data being sent or received in my program so I don't know why that's happening either.
Any help would be appreciated, I'm getting desperate at this stage. I am so close to completion and everything is working except for this horrible humming.
I've even used screened power cables with the screen connected to GND and the metal enclosure, I've laid foil between the lid of the box and the antenna for extra screening, I've tried numerous values of decoupling capacitors at various points on the board, I've tried RC Filters.. nothing I've tried gives me nice clean audio at a reasonable level.
All ideas welcomed!
