A software defined radio basically consists of an RF front-end hardware part and specialized software that performs the processing of this signal. By default SDR software is controlled by keyboard and mouse. If we want to feel the old feeling of tuning the frequency with a knob then we have to make a special device that will give us that pleasure. The simplest and cheapest way to make such a device yourself is by using a PC mouse and a cheap rotary encoder. 

  Specifically, in the project I will use a wireless mouse, so accordingly the tuning button that I will make will be wireless. Any wireless mouse that has two buttons and a scroll wheel can be used. In particular, I used an inexpensive Genius model.

 First, I'll disassemble mouse so we can see the parts it's made of. It consist a blue focused LED, then three buttons, and for us the most important part, this small rotary encoder. I will unsolder encoder and replace it with a more robust one. I will also mount external buttons in place of the left and right buttons. Also I will replace focused led with a small 3mm diffuse LED that will serve as an indication of the device's activity. 

To make the construction as simple as possible, it is desirable, after soldering the wires that are needed for the corresponding external components, to use the part of mouse case again so that we can use the original "Power on" switch, as well as the battery compartment. Here is what the mouse board looks like after soldering the necessary wires leading to the external components. And this is what the soldered tuning wheel looks like inside after mouse modifications.

  The right click is connected to the encoder button. On the bottom side there is a switch and a place for the battery. 

 And finally, the device built in a suitable box.

  I will demonstrate how to work in SDR++ software with RTLSDR USB dongle. Of course, we can use this tuning knob in any SDR software to adjust the receiving frequency. 

In fact, two mouses are connected to the PC, which, as we know, can work independently of each other. With the standard mouse we start the program and set the options and functions of the SDR software, and we modified the other mouse into a tuning button.

  It remains to mark the number of the frequency that we want to change and start dialing. For my SDR radios, I use this old All-in-one PC, which also has a touch screen, so it represents an ideal solution for this device. We simply touch the digit that we want to change.

  Let me not forget to mention that the two buttons, left and right click from the old mouse are very useful when using several plugins intended for this purpose.

   And finally a short conclusion. This is a really cheap and easy to make device that will give us great pleasure when searching to SW stations. The feeling of selecting stations in a retro way with a large tuning wheel is particularly pleasant and takes us back to some earlier days of radio technology.