Buy a kit

kv4p HT makes no money from these sites, but they provide convenient kits:

Or loose parts

SA818-V radio module (DRA818V may be substituted)
SMA male antenna of your choice. e.g. pocket-size antenna or 1/4 wave Signal Stick
Choose one of these 2 connectors (either works, they have the 5.1k ohm pull-down resistors needed to make problem ESP32s work):

Option 1 (Recommended): this short cable and this adapter from Amazon. This option may have better audio quality.
Option 2: this small connector from AliExpress (choose "Color: C female-C-C", be careful because they have similar names!)

NOTE: All three 1.8x PCBs have the same functionality. The only difference is the ESP32 dev board footprint.

Version	ESP32 dev board	PCBWay link	JLCPCB files
v1.8a	1" wide 38-pin ESP32 (example on AliExpress , choose 38-pin USB C)	PCBWay (choose PCB+Assembly)	JLCPCB files (GitHub)
v1.8b	0.9" narrow 38-pin ESP32 (example on Amazon )	PCBWay (choose PCB+Assembly)	JLCPCB files (GitHub)
v1.8c	30-pin ESP32 (example on Amazon )	PCBWay (choose PCB+Assembly)	JLCPCB files (GitHub)

NOTE: v2.0c is also available (from Halibut Electronics as a kit), or from files in GitHub. v2.0x is a substantial improvement over the v1.x line, it does not require an ESP32 dev board, and it was properly engineered by a professional.

Solder the parts
- Solder the SA818-V, ESP32, and SMA connector to the PCB.
- Then, trim all of the ESP32's legs as short as possible (so they don't contact your phone).
3D print the case
- Choose a kv4p HT case on Thingiverse (make sure it matches the PCB version 1.x or 2.x)
- The case looks cooler with 2-colors, which most 3D printers can do (see how)
Assemble the parts
- Insert the PCB into the case until it snaps in
- Cut a strip of sticky gel pad to attach the kv4p HT to the back of your phone
- Screw on the antenna
Install the Android app
- The app requires Android 8 or higher, which came out in 2017 and pretty much all phones with a USB C connector will have.
- You can search the Play store for "kv4p HT", use this link to the kv4p HT app, or scan this QR code:
- NOTE: The first time you run the Android app, it will flash the firmware onto your kv4p HT. It takes about 5-10 minutes.

If for some reason the Android app can't flash your kv4p HT firmware, you can use this web-based flasher. It's not usually necessary.

Plug USB C cable from kv4p HT to your computer (your phone's browser won't work)
Use this online flash tool to install the latest firmware, which requires Chrome, Chromium, or Edge.