MP3 UART voice module on D1 mini pin D7/D8 not working

I run a test with the MP3 UART voice module connecting to an Ardunio Uno on pins ⅔ via the supported cables and everything ran just fine.

So I moved over to my target setup, which is a Wemos D1 mini. I soldered the connection to the only free pins I have left on this project: D7 & D8.

 

For some reason this is not working at all. I get no sounds from the speaker and I am not sure why that is.

when giving power, the busy led on the sound module flashes up, indicating it is powering up.

I took these measurements on the sound module:

- the VCC pin has 3.3 V.- the TX pin has 3.3V (I find this strange. But I never checked the TX pin while I had it all connected via the cable on the Uno)- the RX pin has 0.2 V (intepret this as that the module is receiving a serial connection. I dont have a good oscyloscope to check this further. The one built in my volt meter is just a gimmick and of no use).

This is my code:

 

/*

* @file Voice Module.ino

* @brief

* @n [Get the module here]

* @n This example Set the voice module volume and playback

* @n [Connection and Diagram]()

*

* @copyright [DFRobot](https://www.dfrobot.com), 2016

* @copyright GNU Lesser General Public License

*

* @author [carl](lei.wu@dfrobot.com)

* @version V1.0

* @date 2017-11-3

*/

#include <SoftwareSerial.h>

 

SoftwareSerial MP3(D7, D8); //RX,TX

 

unsigned char order[4] = { 0xAA, 0x06, 0x00, 0xB0 };

 

void setup() {

 

Serial.begin(9600);

MP3.begin(9600);

Serial.println("serial initiated");

volume(0x1E); //Volume settings 0x00-0x1E

Serial.println("Volume set");

}

 

void loop() {

Serial.println("playing...");

play(0x01); //Play the specified audio:0x01-file0001

// Serial1.write(order,4);//order play

delay(2000);

}

 

void play(unsigned char Track) {

unsigned char play[6] = { 0xAA, 0x07, 0x02, 0x00, Track, Track + 0xB3 };

Serial1.write(play, 6);

}

void volume(unsigned char vol) {

unsigned char volume[5] = { 0xAA, 0x13, 0x01, vol, vol + 0xBE };

Serial1.write(volume, 5);

}

 

Is this not working due to using specifically D7 & D8? I remember reading somewhere that you can excplicitly change the pin function to GPIO, but I cannot find it anymore.

I am kind of stranded on this issue and any help is apreciated