Honeywell HPMA115S0, sensor not start again after stop I use HPMA115S0 sensor with Arduino for Nodemcu, i can read it value but face one problem. The sensor not work after send stop measure command (fan not start too).

const int StartPmMeasure[4] = {0x68, 0x01, 0x01, 0x96};
const int StopPmMeasure[4] =  {0x68, 0x01, 0x02, 0x95};
...
void stopSensor() {
  if (isSensorStart) {
   Serial.println("INFO: Stop sensor");
   sendCommand(AutoSendOff);
   sendCommand(StopPmMeasure);
   isSensorStart = false;
 }
}

void startSensor() {
 if (!isSensorStart) {
  Serial.println("INFO: Start sensor");
  sendCommand(StartPmMeasure);
  sendCommand(AutoSendOn);
  isSensorStart = true;
 }
}
I have the same problem here. I'm using a HPMA115S0 with an ESP8266 and found out that the sensor don't respond in general if you are doing a deep sleep with the ESP. If the ESP wakes up, the sensor does not respond on commands till you remove the 5 volts of the HPMA for a short time to make an "hard reset" of the sensor.

I think there is a problem with the ttl-level on the UART-RX-line of the HPMA. Because if you're pulling the rx-line of the sensor manually to ground (maby the ESP is doing this if he goes to deep sleep or wakes up), the sensor does not respond after that.

I spend very much time in this phenomenon. I used different pins on the ESP for software UART and used the hardware UART, problem still exists.
I assume that the ESP pulls all his pins on ground level for too long. That means that the stop bit (high-level), which the sensor wants after 8 bits are transmitted, is not present. This leads to strange behavior of the sensor.
I don't have a digital storage scope to see the level on rx-line, so this is only a presumption. But I don't have this problem, if the ESP idles with an sleep-command.
Maby you are also doing a deepsleep with your ESP which results in the same problem?

Best regards