dragon-radar

The aim of this project is to describe how I have created a reproduction of the dragon radar based on a Raspberry Pi Zero. A video preview is available here: https://www.youtube.com/shorts/0jsaYxSqkwQ

Drawing

Hardware

Bill of materials

Component	Note	The place where I got it
Raspberry Pi Zero	Any Raspberry Pi Zero supplier
SDCard	An SDCard for the Raspberry Pi Zero
screen + driver	Be careful, there are different models of the driver pcb (the dimensions can be different). I personally got this version:	Link
battery		Link
battery charger + boost		Link
power switch		Link
speaker	8ohm speaker (max diameter 17mm)	Link
push button	MSP121CSW momentary switch	Link
mini hdmi connector		C1 from Link
hdmi connector		A1 from Link
hdmi ribbon	50mm	Only FFC -5cm from Link
audio filter + amplifier	see below

A 5V micro USB charger is also required to charge the dragon radar battery.

Audio filter + Amplifier

Unfortunately the Raspberry Pi Zero doesn't offer an easy way to send audio output to an extrenal speaker. An audio signal can be retrieved from the GPIO 18. This signal must be filtered and amplified before being sent to a speaker. I have designed a specific PCB to perform these tasks.

Kicad project

audio-pcb-kicad-project.zip

Bill of materials

Component	Number	Package
Capacitor 390 nF	1	SMD 1206
Capacitor 1 uF	2	SMD 0805
Capacitor 33 nF	1	SMD 1210
Capacitor 10 uF	1	SMD 1210
Resistor 20K	2	SMD 1206
Resistor 270	1	SMD 1206
Resistor 150	1	SMD 1206
8002 audio amp IC	1	SOIC 8

I sent the PCB gerber files to PCBWay then I sold the components on it.

Connection diagram

Fixings

To fix components inside the case I used glue sticks and inserts/screws for some PCBs. The M3 inserts used are: Link.

Case

I have designed the case using Fusion 360.

Here are the files: case.zip

For a better result I have sent the STL files to Sculpteo.

• Material: SLS (Plastic), Nylon PA12 100-120µ (White)
• Finition: Polish, White

Assembly

Back

1. Case back

2. Add push button

3. Add power switch

4. Add LCD driver + HDMI plug

5. Add battery charger + boost

6. Add Raspberry Pi Zero + HDMI plug

7. Add audio filter + amplifier

8. Add speaker

9. Add battery

Front

1. Case front

2. Case front

The button cap is simply clipped on the push button.

Software

For this part there are two different ways:

1. Using Raspberry Pi OS:

   • Install Raspberry Pi OS on the SDCard.
   • Configure the system to send output audio to GPIO 18 (adding dtoverlay=pwm-2chan,pin=18,func=2,pin2=13,func2=4 to /boot/config.txt should do the trick).
   • Add the dragon-radar program, compile it and configure the system to run it at start.
   • Configure the system as read only filesystem.

2. Using Buildroot to create our own customized Raspberry Pi Zero image. This is more complex but should boot fastest.

I personnaly choose the second way, the pi zero image can be found here: sdcard-dr-snd-hdmi-init-fast.zip