Robie Jr Remote with Arduino

thingiverse

I purchased this Radio Shack Robie Jr on Ebay several months ago, and it was listed as a parts-only machine in pretty bad shape with no remote and missing grippers, plus the gears on the wheels were stripped. I had another Robie in good condition with a remote so I decided to recreate its remote using a 3D printed case and an Arduino controller. The remote doesn't use RF or IR signals like most remotes are familiar with; it uses ultrasonic sound. This means we need an ultrasonic transducer for the Arduino to drive, and fortunately they're cheap and easy to find now because they're used in ultrasonic distance measuring modules for hobby robots. I got the one I used from a Banggood HC-SR04 module, and I just desoldered the TX transducer from the board and drove it directly from 2 Arduino digital pins. First, I needed to examine the signals coming from the working Robie Jr remote I had. To do that, I used one of the cheap Ebay Logic analyzers. I took the remote apart and with a little reverse engineering, I found the pin coming from the microcontroller that drives its transducer. The remote has four direction buttons and a follow switch. When the follow switch is on, the robot heads toward the remote. The robot has an ultrasonic receiver in each of its shoulders so it can determine which direction it needs to steer to. I used the Logic analyzer to record the signals from the remote for each direction button and the follow switch. The protocol is pretty simple: when the forward button is pressed, the remote puts out a constant 41.7 kHz signal. The other direction buttons and the follow switch produce a 1.982 millisecond burst of the 41.7 kHz carrier signal followed by a silent period and then another 1.982 millisecond burst. That is repeated until the button is released. The length of the silent period varies depending on the button pressed. Here are the values for each direction: Forward: continuous 41.7 kHz carrier Reverse: 1.982 millisecond bursts of carrier separated by 0.143 seconds of silence Left: 1.982 millisecond bursts of carrier separated by 0.133 seconds of silence Right: 1.982 millisecond bursts of carrier separated by 0.123 seconds of silence Follow: 1.982 millisecond bursts of carrier separated by 0.113 seconds of silence The code was written using version 1.8.5 of the Arduino IDE, and some of the delays were produced using delay loops, so future changes in the IDE or compiler might break the code. I'm sure the code could be done better, but it works. I used Fusion 360 to design my remote's case, which is made up of five parts: the top, bottom, front, switch plate, and clamp. The switch plate is the only part that was printed with a barb on the bottom so you have to flatten them out with pliers. I designed my battery compartment so the solder tabs are on top. The power and follow switches are held in place by a printed clamp, so you have to use switches of the right size. I used Dupont wires and headers on the Arduino Pro Mini, but they take up a lot of room, so next time I would just solder the wires to the board. The Arduino is hot glued in the case. I used a 2 x 6 male header soldered to a piece of prototype board as a power distribution strip for the Dupont connectors. The range of my remote is about 5.5 meters.