Howto For Creating a Digital Scanner for the Raspberry Pi 4

Introduction

This guide will show you how to create a digital, trunked Raspberry Pi 4 scanner using an RTL SDR and SDR Trunk software. Top of the line digital scanners cost upwards of $500-$600, this project will cost about half of that with a lot of flexability in how it can be implmented.

My goal with this was to create as close to an all-in-one solution as possible, where there was only one thing to plugin and it is fairly portable.

Note: this will NOT work with anything less than a Raspberry Pi 4 with 4 Gb of RAM. The lower Pi's don't have enough "horse power" (CPU or RAM) for this application.

Step One: Parts List

Here are a list of parts you'll need, some of these things can be obtained at Microcenter for lower prices so if you have one near you, check there first. One option is a kit which will give you more than you need, but will cover items 1, 3, 10 and possibly 11. It may be a little more cost effective. https://www.microcenter.com/product/615270/canakit-raspberry-pi-4-starter-max-kit-(4gb-ram)

A Raspberry Pi 4 with at least 4 Gb of RAM (8 Gb works too if you'd like): https://www.amazon.com/Raspberry-Model-2019-Quad-Bluetooth/dp/B07TC2BK1X or Microcenter: https://www.microcenter.com/product/609038/raspberry-pi-4-model-b-4gb-ddr4
Raspberry Pi 7 inch touchscreen: https://www.amazon.com/Raspberry-Pi-7-Touchscreen-Display/dp/B0153R2A9I or Microcenter: https://www.microcenter.com/product/613535/raspberry-pi-7-touch-screen-lcd
A high quality power supply, I like this one (you can get one with a switch for $1 more): https://www.amazon.com/CanaKit-Raspberry-Power-Supply-USB-C/dp/B07TYQRXTK or with switch: https://www.amazon.com/CanaKit-Raspberry-Power-Supply-PiSwitch/dp/B07TSFYXBC
A good cooling fan, I used this one as the Pi will be running at around 30-50% CPU pretty much 24/7 with will be overclocked (as an optional step) and we will need to keep it cool: https://www.amazon.com/gp/product/B07ZV1LLWK
A case, I used this one because of it's large size which gives plenty of room to move around and route stuff inside: https://smarticase.com/collections/all-products/products/smartipi-touch-pro (choose the large size). You can also add on the external micro SD card access, but this is optional.
You'll also need this extra part for that case (choose the one with USB and audio jack from the drop down list): https://smarticase.com/products/usb-and-audio-jack-extender-for-smartipi-touch-pro
An RTL SDR dongle: https://www.amazon.com/NooElec-NESDR-Smart-Enclosure-R820T2-Based/dp/B01HA642SW
An antenna: https://www.amazon.com/gp/product/B07HLKKHCM
As for sound options, in wanting to keep this as a single unit with one power cord, I chose this USB speaker: https://www.amazon.com/gp/product/B086JXJ1LF. It's size matches the case, the sound quality is decent, and the cord can be hidden behind. The problem with this speaker is that in combination with the RTL SDR dongle they will draw too much power from the USB bus and you'll get over voltage errors which will also an annoying clicking sound and won't work at all. I got around this buy creating USB power cable that plugs into the 5 volt and ground pins on the Pi and paired it with this splitter: https://www.amazon.com/gp/product/B00NIGO4NM. If you don't want to go to that much trouble, you could just use a pair of cheap powered computer speakers that plug into the 3.5 mm port, it just means there will be two wall warts rather than one. Another option is this USB speaker: https://www.amazon.com/gp/product/B075M7FHM1, it will not be very loud and the sound quality is so-so, but it get's the job done and doesn't draw too much power.
MicroSD Card: There are some options here too, but any class 10 or A1/A2 card should work like this one: https://www.amazon.com/SanDisk-128GB-Extreme-microSD-Adapter/dp/B06XWMQ81P
A USB SD/MicroSD card reader (unless there is one on your PC already, many laptops have them): https://www.amazon.com/Anker-Portable-Reader-RS-MMC-Micro/dp/B006T9B6R2
USB Extension Cable: https://www.amazon.com/C2G-52119-USB-Extension-Cable/dp/B00CJG2ZYM
An SMA extension cable: https://www.amazon.com/gp/product/B00COJWKGC
A keyboard: https://www.amazon.com/gp/product/B07VR5Y39T
Optional: Right angle USB extension cords, these give a cleaner look if you're using the USB speaker: https://www.amazon.com/gp/product/B07CF7243G
Optional: The above cooler (from #4) has a fan with LED's on it, if you don't want with that you can get this fan as a replacement: https://www.amazon.com/gp/product/B00NEMGCIA, and you'll need these too: https://www.amazon.com/EDGELEC-Breadboard-Optional-Assorted-Multicolored/dp/B07GD2BWPY

Step Two: Install Operating System On Micro SD Card

Install the Raspbery Pi imager on your computer: https://www.raspberrypi.org/software/
Insert the microSD card in your computer and open Raspberrry Pi Imager
Click Choose SD Card and the card that is inserted should be the only option, choose that one.
Click Choose OS and scroll down to Ubuntu and click on it, then choose the LTS version of the 64 bit server, for example: "Ubuntu Server 20.04.2 LTS (RPi 3/4/400)" the line under it should read "64-bit server Os with long-term support for arm64 architectures" The latest version may be different, but the important part is to choose LTS 64 bit.
Click the Write button and the OS will be loaded on the SD card.
Once done the imager will say the card can be removed from the reader, click continue and close Raspberry Pi Imager.
Eject the card and reinsert it and if using Windows ignore any warnings that pop up.
Go into the folder (if on Linux it's the system-boot folder), and open network-config with a text editor.

Comment out all the lines and add the below lines to the bottom, be sure to keep the spacing intact, note there are two spaces for the indent:

version: 2
renderer: networkd
wifis:
  wlan0:
    dhcp4: true
    dhcp6: true
    optional: true
    access-points:
      "SSID":
         password: "PassPhrase"

Change SSID to the name of your WiFi (make sure it is in quotes) and same with the password (also in quotes). The Raspberry Pi WiFi only works with 2.4 GHz WiFi's and will not work with 5 GHz ones. Also if your WiFi has security, it will only work with WPA 2 Personal.
Next edit user-data in a text editor and add the following to the bottom (also keeping the spacing intact):
```
## Reboot after cloud-init completes
power_state:
  mode: reboot
```
Save both files take out the card and insert into the Raspberry Pi.

Step Three: Case Assembly

Follow the instructions for assembling the Raspberry Pi, touchscreen here, but see the below exceptions: https://cdn.shopify.com/s/files/1/0793/8029/files/touch_pro_assembly_instructions.pdf?v=1615409778
On Step 4 and 5, skip the red and black wires as they will not be needed.
Skip step 6 as we will be using the extender plate ordered from Smart Pi (number 6 on the parts list above).
On step 7 we will be mouting the Raspberry Pi at the inner position (the second image and instructions) and secure the Pi into that position using the standoffs that come with the cooler. Also make sure the silver part of the ribbon cable faces the white part of the fastener.
Skip step 8, there won't be a camera.
On step 9, I used the adhesive front panel.
If you purchased a USB speaker, you may want to run the cord under the bottom of the case (between the base and top), do this before step 10.
On step 11 use the door, but you may wish to drill small holes for air curculation for the fan on the cooler.
Skip step 12-14.
Before step 15 follow the below instructions.

Extra Assembly Steps

Drill a hole in the back of the case for the antenna and mount the cable from parts list #13.
Drill holes in the back panel cover for air circulation and mount it.
Install the cooler fan from parts list #4 and optional fan (parts list #16), note how the stand offs that come with the coller are used to screw in the Raspberry Pi and the screws that came with the case screw the cooler into the stand offs. (opposite from the instructions for both).
If you are using the USB Speaker from parts list 9 (the first one) that uses too much power, then I created the cord in the below picture, I purchased these: https://www.amazon.com/gp/product/B081JGZK14 and soldered a red and back juper wire on to the plus/minus pins of the USB (the two outer ones) and plugged them into a 5v pin and ground:
As you can see from the image above, how to add in the plate from parts list #6 which I plugged into the USB splitter from parts list #9 which is wrapped around the cooling fan.
Plug in the two cables according to the instructions from the case instructions step 15.
Next with plug in one of the USB extension cables (parts list #12), the USB dongle from the keyboard (parts list #14) and the USB splitter which plugs into the USB cable from the plate and the 3.5 mm plug for the audio port from the plate.
Then plug in the RTL SDR dongle from parts list #7)
Once all the above are connected, assemble the rest of the case, it will be a tight fit, but it will all fit in there. Then attach the antenna from parts list #8
If you purchased the right angle USB cables from parts list #15 attach that so it faces the back and plug the speaker into it. Here's a look at the finished product (if using the USB speaker)
At this point you can use velcro to adhere the speaker to the case if you would like.