It's likely that many people have considered whether smartphones could replace handheld consoles, or at least serve as an operating interface (especially for manufacturers with a strong Japanese influence).
HoweverKV4P HTThe project aims to achieve this goal by transforming Android phones into more modern, portable handheld devices.
The KV4P HT project consists of two parts: a mobile application and hardware. The mobile app can be found directly on Google Play, while the hardware needs to be either self-made or purchased. The KV4P HT app connects to an ESP32 via USB OTG functionality on the phone to communicate, and the ESP32 controls the SA818 radio module based on settings in the mobile app. Since the SA818 module comes in two versions (UHF and VHF), the KV4P HT can only be used as a single-band device.
The KV4P hardware currently has two versions: the original version v1.x, designed by the original author, which uses an ESP32 development board; and the v2.0x version designed by Bimei Electronics. In the v2.0 version, the ESP32 module and USB serial chip are directly soldered onto the main board. Additionally, v2.0 has a better filter. Both versions are open source and can be found in the project's repository. Neither version includes an amplifier, so the output power is 1W, which is the same as the SA818. The latest version of v2.0d was created this time.
Although I chose the v2.0d version, I regretted it once I started building. Aside from the difficulty of sourcing components domestically, the construction process is also significantly different. Unlike the v1.x versions, which only require soldering a few simple components with a soldering iron, the v2.0x series designs do not consider manual soldering at all. The spacing between some components is very small, and if the assembly order is incorrect, it can be very difficult to fix. For example, the USB interface is located close to the CP2102. After soldering the CP2102, soldering onto the USB interface becomes more challenging. Similarly, the tantalum capacitors are also very close to the ESP32, making it necessary to solder and adjust the perspective just to see if the ESP32 has been soldered correctly. In addition, the 0402 capacitors used in the filter section are so small and located very close to the large coil inductors that they are easily pulled into the inductor by surface tension. However, the v2.0d actually provides ample space for utilization. Aside from potentially using colored LEDs in the future, the two large-space pin headers on the right side are completely unnecessary, occupying a significant area (presumably someone wants to connect a string of lights there?). Overall, if you have access to equipment like a hot plate and desoldering station, you can try the v2.0x series. I recommend using a steel mesh to minimize manual adjustments and surface tension issues. For beginners who only use soldering irons, the v1.x version is more suitable. Both versions have the same functionality and are not significantly different in size. Purchasing the development board does not cost much more than purchasing the ESP32, CP2102, and other components separately.
Once the device is assembled, it's time to use it. After connecting the C2C line to your phone and opening the KV4P HT app, it will automatically prompt you to flash the firmware. Simply click "Install" and wait a moment for the process to complete. In the app settings, you can enter the call sign used for APRS messages, select the frequency range for the SA818 module, and set the noise reduction level. Thanks to the advanced Android system, you can also enable subtitles in the settings, allowing you to listen without any sound issues.Can those low-powered handheld devices actually do it?
Return to the main interface, where you can directly enter the frequency at the top of the screen and select channels from the list. To add a channel, click the "+" button in the bottom right corner. Thanks to the virtually unlimited storage space on Android phones, you can add an unlimited number of channels here. Finally, press the large white button or the button on the side of the KV4P HT mainboard, and you can speak into your phone.
In addition to voice communication, it is also possible to send and receive APRS text messages. Unfortunately, due to the decoding capabilities of FT5D, it has never successfully received text messages sent by KV4P HT. However, text messages sent by FT5D can be successfully received and displayed by KV4P HT.
Currently, the only features available are these, which can only satisfy basic voice calls and APRS text messages. Other functions are completely absent, and even the settings options are not comprehensive. For example, the signaling system only supports sub-audible noise suppression, but there is no support for scanning dual-watch, APRS paths, or channel export/import. However, the main function of the KV4P HT can be achieved through a mobile application, and various functions can be added through continuous iteration and upgrades. In principle, other projects using SA818 can achieve similar functionality, including digital voice. However, at present, the KV4P HT is still just a toy for enthusiasts.
Finally, the KV4P HT unit was integrated with Fujitsu, and it can also be considered a Japanese handheld device.
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