Using the comport object in Pure Data

I’m building a Raspberry Pi 4 based device that uses a thing called Pure Data to play sounds in response to incoming MIDI messages. The device also has a controller and display which is controlled by a Raspberry Pi PICO. I’ve connected the hardware for a serial connection and discovered how to send serial messages from the Circuit Python program in the PICO. Now I need to get the messages from the PICO into my music making software. This is how to do it.

The above patch fragment (is that even a thing?) shows how it we can surface serial data in a Pure Data patch. However, before we can do this we have to add the comport object to your Pure Data installation. If you re using a Raspberry Pi it turns out that this is very easy:

sudo apt install pd-comport

This console command installs the comport object. Now we can add one to our patches. The patch above shows that we can send it messages to make it do things. The message on the left sets the device name. The second messages sets the baud rate. The third message asks the comport to display all the available comports that Pure Data has found.

When the above patch is triggered by a message on the inlet it will set up a comport and set the baud rate to 19200. Any messages that we send to the comport object will be sent out of the comport. These need to just lists of bytes. If the comport receives any bytes from these are sent out of the bottom of the comport object. In a while we’ll take a look at how we can encode and decode messages that we want to send over the serial connection.