Controlling a Ultrasonic driver board with Arduino

I Have a Ultrasonic driver board that is activated with a momentary switch acting as a toggle (click turns it on - click again turns it off).

As the main chip has no writing on it, how would I probe it to find out what pins do what and interface a Arduino with it?

What i know so far:

The board has heavy debouncing on the button so controlling it by putting a transistor switch over the button will not work, as i need to switch this on and off in 100ms intervals. The debounce seems to be about 1000ms

Short press toggles PWM output. Long press toggles LED's on the back of the board.

With a multimeter I have found the pin that reads the button, +5V and Ground

My Goal is to control this board with digitalWrite() from a arduino or a transistor switch controlled by a arduino.

#include <SoftwareSerial.h>
SoftwareSerial HM10(2, 3); // RX = 2, TX = 3
char appData;  
String inData = "";



void setup()
{

  Serial.begin(9600);
  Serial.println("HM10 serial started at 9600");
  HM10.begin(9600); // set HM10 serial at 9600 baud rate
  pinMode(5, OUTPUT); // onboard LED
  digitalWrite(5, LOW); // switch OFF LED
}

void loop()
{
  HM10.listen();  // listen the HM10 port
  while (HM10.available() > 0) {   // if HM10 sends something then read
    appData = HM10.read();
    inData = String(appData);  // save the data in string format
    Serial.write(appData);
  }


  if (Serial.available()) {           // Read user input if available.
    delay(10);
    HM10.write(Serial.read());
  }
  if ( inData == "a") {
    Serial.println("Power off");
    digitalWrite(5, LOW); // switch off
  }
  if ( inData == "b") {
    Serial.println("Power on");
    digitalWrite(5, HIGH); // switch On

  }
}

Can you please explain how you come to know this: "The board has heavy debouncing on the button so controlling it by putting a transistor switch over the button will not work, as i need to switch this on and off in 100ms intervals. The debounce seems to be about 1000ms".

How do you know this is not how log it takes the piezos to begin to operate.

Paul

I have another driver with a momentary activation and similar hardware that will activate a run at full power instantly, but the shape of the board makes it not usable, so that's why i'm trying to workout how to control this one.