First we need to understand the Red Green Blue color format, for each component we have a possible value between 0 – 255, meaning that each component has a resolution of 8 bits. Let’s create a protocol to send color information to a microcontroller in RGB format, with the goal of controlling a RGB Led. Creating one it’s not complicated, the easiest protocol is just a fixed length data sequence that provides a known header. It becomes clear that if we want to transmit complex data, we have to conform with a protocol or create one. For example, the TCP protocol is defined as: Some protocols define fixed data length, others more complicated are designed for variable data length. We can’t just send data bytes and hope someone understand them. We have by example TCP and UDP protocols, which are the basis of internet data exchange.Ī communication protocol consists of a well designed data pattern. This a common checksum validation methodSending and receiving multiple bytes of information efficiently between microcontrollers, sensors or computers requires the design of a communication protocol. We'll employ PWM to control each RGB Component in the Led perform checksum validation, it's optional but really suggested get checksum value from buffer's last value, according to defined protocol prior overflow, we have to restart readCounter store received byte, increase readCounter this conditional is implemented, so that we don't restart readCounter It's possible the header appears again as a data byte. If it's the first time we find the header, we restart readCounter given the case we must ignore it and restart our reading code. We must consider that we may sometimes receive unformatted data, and After summing we need to AND the result to a byte value. We perform a sum of all bytes, except the one that corresponds to the original int is a signed 16 bit value in Arduino 8 bit boards.
After the shifting we AND the result because the value is a 16 bit value Bitshifting is faster, but a little harder to understand. Dividing is easier to understand, but computes slowly 2 - Bitshift Right by 2, to obtain and effective 8 bit value. 1 - Divide our 10 bit value by 4, to obtain and effective 8 bit value. 10 bit max value is 1023, 8 bit max value is 255. analogRead() returns a 10 bit value, we need to scale it to a 8 bit value. we define our header byte only once, we're not going to change it
Serial communication protocol arduino code#
The following code will be downloaded to the first Arduino (the one with the potentiometers):
Serial communication protocol arduino serial#
They will be connected through their UART pins (Arduino Serial Library employs UART). One will have 3 potentiometers, one for each color component (Red, Green, Blue), the other one will have an RGB Led connected to it. We are going to employ two Arduinos for testing. The following table illustrates the protocol we’re going to use: Validation gives us assurance that the data we receive is not corrupted (sometimes by unknown causes we might have data corruption, for example: a bit value changes by electromagnetic effects in the transmission line, the color might change dramatically by this cause). Every package we send/receive will have a length of 5 bytes. We also require a header to identify the protocol, and optional but extremely suggested is the use of a checksum byte as a validation method, this gives us a protocol with a fixed value of 5. Our protocol needs to implement a minimum of 3 bytes (1 byte equals 8 bits) to contain color data in RGB format. So… the RGB format defines a 24 bit color.
Sending and receiving multiple bytes of information efficiently between microcontrollers, sensors or computers requires the design of a communication protocol.
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