But imagine, for example, that the receiving Arduino is powered off and then back on.

Now if the receiving program is “in sync” – if it starts reading from the beginning, it will receive the numbers all right. Here is what the sequence of chars coming from the serial line could look like: Our program in another Arduino is receiving the numbers and it needs to run its loop 10 times per seconds to control the nuclear reactor in your basement. Suppose one Arduino is sending numbers (fixed 3 digits length) once per second. In this code, I assume that the data/command are 3 chars long and I only do the processing if there are exactly 3 characters received. But you cannot stop your loop and wait! You want to keep processing the inputs and controlling outputs 10 times per second – imagine your program controls a quadrocopter it cannot just stop controlling the aircraft and wait for the data to arrive from serial line.Īnother solution is to change the condition to something like this: One solution would be to wait for all data to come something like calling Serial.readStringUntil which will read until a terminator character is received or there is a timeout. There may be just the first char, or the first two chars, etc. If your data or command is more than 1 char long, there is a good chance that you cannot process it yet because it is not completely received. The condition is true if there are one or more characters available. Well, you put if (Serial.available() > 0) into your loop and if there are some data (or command), you process it. Now you want your program to respond to commands sent from the serial line or to process data sent from another Arduino. You make your loop code run fast, for example, it is executed 10 times per second. You have a program which is doing lot of things – reads the sensors, controls outputs, shows current status on a display, etc. Let me explain what I mean by an example. It may seem easy but often you run into problems. When writing Arduino programs, you sometimes need to receive some commands or data from serial line.

Arduino fast serial read