hello everyone .
i have a hc-602 ultrasonic sensor and use esp 8266 as microcontroller . i connect the sensor to 5v 1a electricity and the gnd of sensor and microcontroller are common .

when i monitor that i receive some value , the first values always are wrong, but after some wrong value the data will be correct without doing anything .
my question is why first values of the sensor are wrong ?
any idea ?

 

why first values of the sensor are wrong ?

I'm not familiar with that sensor, but many circuits take a little while from switch-on to stabilise. For analogue circuits this may be due to capacitors charging. For digital circuits it may be due to boot-up/initialisation routines.

 

i have a hc-602 ultrasonic sensor

I cannot find any reference to this number. Are you sure it is correct?

 

I’m not familiar with the ESP MCU, but the ADC in ATMega MCUs are recommended to throw away the first value whenever switching channels. And I understand that it has to do with the capacitance of the ADC.

 

I’m not familiar with the ESP MCU, but the ADC in ATMega MCUs are recommended to throw away the first value whenever switching channels. And I understand that it has to do with the capacitance of the ADC.

An erroneous first value could indicate an acquisition time that is too short.