This is article 2 of the series on building a Radio. A key part of the project is the interface; I wanted to keep 100% of the original radios look and feel; that meant somehow I needed to use the knobs in the front along with the spinning the dial. The solution I came up with was to use an Arduino microcontroller, more specifically the Arduino Uno, to handle all the hardware interactions. This article will look at how it was hooked up, along with the code used for it. For the purposes of this article I will not go into too much detail about the parts, and allow the reader to research where needed.
In total there are 5 “devices” hooked up to the Arduino, the first three of these were the knobs. The volume knob, an original knob that came with the unit, feeds the Arduino a number, 0-1023 using a 5 Volt line, then that was mapped to a number between 0-100 to make life easy. The leftmost knob goes between AM/FM/AMC, and on my unit I could never get a stable reading out of it to feed the Arduino, so this knob is actually disabled on my final product. I could have replaced that knob with another, but I felt the project was great without that, along with it would have added a lot of work and stations to make. The center knob is a 10kΩ potentiometer I bought from makershed.com, they seemed to have a size that fit well; I had to drill down the inside of the plastic knob, but that’s how these things go. The two wires I got from the potentiometers each went into their own analog pin, I used 5 for the volume knob and 2 for the station, but this is completely arbitrary.
At this point I should mention that devices like the servo came with a little header on their wires. I took that piece on, and soldered a good wired onto the end to put in the Arduino. The wire the servo came with was thin and didn’t go in a pin well. Moreover all the parts needed power, so I got a tiny bread board from THE SHACK, took over one two row part of it that had double sided tape and put it in the radio. Then whenever I needed 5 volts, I could just use another pin in the bread board. You can see this in the photo below.
The next device to hook into the microcontroller was the servo, now as I said in the last article where I went over me tearing parts out of the original unit; the station knob was done with a string and a sensor and awfulness. Thus, I am using a servo instead; the code gets the input from the station knob, and then adjusts the servo to that mapped value. I got a HexTronik HXT900 Micro Servo 9g/1.6kg off Amazon for cheap; it works well, is tiny, and did everything the project needed; yet, it is fairly loud, so if that is important to you (when the station changes you hear it) then you may want another one. I put the servo in Pin 9 on my Arduino.
The last little device that was hooked up just for fun was a little yellow LED; my radio had a burnt out bulb next to the dial, so I replaced that with a LED. The 13 pin on the Arduino Uno already has a resister on it for a LED so I just put it in there.
The code is fairly simple and straight forward, it reads all the knobs, adjusts the dial when needed, and then sends all its readings over USB to the PC doing the music playback. The baud rate is set for 9600. The one little problem the Arduino code gave me that I didn’t foresee was I needed a set “packet” length to go to the pc, thus when the PC reads the line it knows if it got the whole data set or not reliably. To do this I have a set pattern that the data is fit into. It goes | then whatever the volume is | channel number | and then enough dashes to fill up 10 characters. So an example could be |100|5|— . I thought it was a fun and interesting little quirk.
The system waits 200ms, to let the values change and stabilize if they want, then does it all again. I am used to desktop programming where 100% CPU is bad, so I treated this similarly by habit, but you could speed it up if you wanted. The code is going to be in here to follow (its pde, but rename to TXT works too), along with a picture of the wiring (though some wiring may have changed in final product, old picture).
One part I have yet to mention that is a critical component is the speaker, I used the speaker that came with the unit. I cut the wire from the original circuit, then got a 3.5mm stereo jack from THE SHACK and soldered the wires onto that after making sure that I got positive and negative in the write positions. I can’t guarantee this will work with all radios but that plug was able to go right into a USB audio card I used.
Feel free to email or post with questions. The next part will be the PC and the software running all of this.