You can build a sophisticated computer-controlled radio signal generator with a few parts and a bit of wiring. Here’s how.
A signal generator is a very useful piece of test equipment for a home electronics lab. It can be used to create radio frequency signals to test your circuit designs. It can also be used for home-made receivers and transmitters as a variable frequency oscillator or VFO.
In the old days (and by this I mean more than 10-15 years ago ) building a good quality signal generator or VFO would take careful design and hundreds of parts. Or, if you purchased one, it would cost hundreds or thousands of dollars.
Today, you can just be a good systems integrator. The four parts shown above cost under $18 total.
Signal Generator – How the parts fit together
Here is what they do and how they fit together.
- Synthesizer. This little module is available on e-bay for under $9 (all prices USD). This direct digital synthesizer forms the heart of the signal generator, with a range of 40 MHz and an output of around 1 volt. It works off a five volt power supply. The output frequency can be programmed with parallel or serial data. For my purposes, I will use a couple of pins on my Arduino to connect to the synthesizer for frequency control. This is the most expensive part and also the most complex module.
- Computer. The basic Arduino UNO is more than powerful enough to control the synthesizer, manage a display and controls, and connect my signal generator for computer control. The nice part about the Arduino is that it is easy to change the control program later if I think of new ideas for the test equipment. You can buy an Arduino UNO clone for under $4.
- Display. The LCD 1602 Keypad Shield for the Arduino is also available for under $4. It contains a 16X2 display (two lines of sixteen characters each). It also has five push buttons which can be programmed to control your device. In my design, the push buttons will send commands to the Arduino, which will in turn program the synthesizer frequency. The LCD display will be used to show the frequency and provide a control menu.
- Encoder. Every good signal generator needs a knob. Well, actually it doesn’t. But I want the choice of having a tuning knob to use in addition to the push buttons. The device shown is the KY-040 optical shaft encoder. This is just like the knob you have on your car radio – you can hear 16 little clicks as your rotate it. The KY-040 costs $1 on e-bay.
These four parts, together with a bit of wiring, will be assembled inside a 3D printed enclosure. I may want to add an amplifier and some extra filtering later, so I will leave room in the box for that. Also, I will make a little printed circuit board to hold the synthesizer module and encoder. In addition, I will include a connector for an external power supply or battery, so I can use the signal generator without connecting the Arduino to my PC.
Lastly, I will have to write the software for the Arduino. This should be easy because I have already done the software for the AD9850 module and there seems to be lots of software available for the LCD Keypad.