KV4P V2.0c HT build is complete and functioning well!

I'm happy to report that last weekend I completed the KV4P V2.0c HT build and it's a great success after a couple of bumps in the road. 

For those of you that haven't heard of this project, it's the brainchild of Vance K4VP, who designed a cool PCB and accompanying Android software that allows you to turn most native Android devices (think phones and tablets) in a functional 2-meter HT that supports FM analog and APRS at around 1 watt output. 

I purchased the version 1.8c rev of the PCB and assembled it, which required some light soldering of an inexpensive SA818-V RF module acquired via Ali Express ($10.30 for 2 units including shipping) and an ESP32 microcontroller ($28.99 for 5 of them on Amazon) to a PCB that was created via PCBWay. Total investment around $35. Unfortunately, I couldn't get the v1 board to work reliably; it would work and then the app would lose connectivity with the PCB for an unknown reason.

A little while later, I was listening to the Ham Radio Workbench podcast when I learned that Mark Smith N6MTS, proprietor of Halibut Electronics and regular on the podcast, had designed an improved version of the KV4P PCB and was selling it for $59, including a pre-populated ESP32. I ordered one and a couple of weeks later it arrived. Mark's board does still require an RF module, and fortunately when I ordered it for the original build, it came in a 2-pack, so I already had everything I needed. In addition to a cleaner design, the V2.0c PCB also features dual PTT switches (more on that later). 

It took about 10 minutes to solder the RF module onto the PCB, about an hour to 3D print the case designed by Vance (print files are on Thingverse). I had already installed the KV4P App from the Google Play Store on my Android "project phone" (a Blu View 5 pre-paid phone that I bought for $35 at Wal-Mart). The PCB attaches to the phone via a USB-C connector, which also provides power to the HT, so no external battery is needed. I should mention that there are several versions of the case to choose from: I chose the "right-hand" case that has a PTT "button" on one side, assuming you will be operating the HT using your right hand. 

After making the initial connection to the phone, the app wouldn't recognize the PCB. I assumed it was due to the ESP32 needing initial firmware installation. I first tried the web-based firmware installer on the KV4P website, but it didn't want to work. Then I realized I probably needed to install the USB driver (I'm using a Mac), so I installed that. Still no dice. Lastly, I read that sometimes the ESP32 needs to be booted by holding down the reset button, applying power, then pressing the program button briefly, and releasing the reset button. That did the trick and I was able to install the firmware.

Next, I reconnected the HT to the phone, and the app needed to do another firmware update, which took about 2 minutes. After that, the app recognized the PCB and I did a couple of test transmissions, raising a local 2-meter repeater and hearing myself on simplex. 

I ran into one more issue after putting everything together in the case. While the app was working OK, I couldn't get the PTT buttons to work. I put a message out on the "kv4p HT" Discord channel and Vance quickly replied that sometimes the case can be an issue, causing one of the PTT buttons to be constantly depressed. So I broke out my handy Dremel and removed about 0.5mm from the inside of the case on the side opposite the case's PTT "button". That did the trick--after reassembling everything, the PTT switch now works. I should also mention that I used a couple of removable adhesive pads to secure the HT to the back of the phone, which works great (they're described on the KV4P website). 

Later on I did a few advanced tests, including using the HT to squawk my location via APRS, and sending APRS text messages from the KV4P HT to and from my Yaesu FT5DR. Pretty cool!

So, while there were a few bumps here and there, I'm very pleased with the final result. It's a fun and relatively easy project to assemble, doesn't cost a lot, and it certainly makes for an interesting conversation piece! I'm thinking I might do some experimentation with the USB-C interface to see if I can get it working a Python or C program (eg without the Android phone), enabling it to be controlled via a Raspberry Pi, Android or a laptop. Vance has generously published the source code for both the ESP32 and the Android app on github, so I don't see why this wouldn't be possible. A pair of them would make an inexpensive way to exchange data via APRS. If you need help, Vance has created a Discord channel for community support (which he monitors regularly), 

I'll keep you posted!