If you’re chaining multiple controllers together, only one of them needs pull-up resistors. Note that there are two spots for 4.7 kOhm resistors on each controller. The controllers each have two sets of inputs for power and I 2C communication so multiple controllers can be chained together on the same bus.

The gerbers are formatted for fabrication by OSH Park, which I highly recommend for low-volume jobs. If you’re interested in making your own, you can download my eagle files for the schematic, board layout, and the gerber files for fabbing the PCB. My sonar controller basically consists of an ATtiny84, with eight inputs for HC-SR04 ultrasonic rangefinders.

That’s really all there is to it! The protocol is simple, but there’s some fiddly details to work out in the code. If you’re not familiar with I 2C I’d suggest reading up on it. One other difference with the Raspberry Pi to Arduino protocol is that we’ll be using I 2C instead of serial. The Arduino assembles the bytes into 8 16-bit ints.The ATtiny sends its readings back to the Arduino as 16 bytes.The byte has no meaning, it’s just a flag to signal the ATtiny to ping its sensors.The ATtiny then pings all of its sensors and sends back the readings when it’s done. The communication protocol is going to be very similar to the one that I outlined for communicating between a Raspberry Pi and an Arduino, only simplified. Basically, the Arduino tells the ATtiny when it needs updated sonar readings. Then we’ll look at the physical layout of my sonar controller.We’ll start by defining a communication protocol.As with my earlier post on Raspberry Pi to Arduino communication, there’s several steps to this process.

Attiny88 wire library