Ringo is a cell phone kit — period. What can you do with it? Assemble a cell phone yourself! And why would you do that? Of course, to learn how such a device works “in principle.”

Insights into the hardware and software of cell phones are hard to come by, as they are among the most modern technologies that have been developed in recent years. After all, Apple and its competitors have made hundreds of billions of dollars with smartphones over the past decade. So, why build such a device yourself? Are you automatically following in Steve Jobs's footsteps? Certainly not. Or does it give you the knowledge you need to hack such devices and take over entire companies or networks? Probably not. But you can learn to understand a phone's basic functions and how they work. That’s something. Plus, Ringo is an ideal Christmas present, which the offspring can benefit from for longer because they can learn a lot during assembly (with a little help). The kit, referred to by CircuitMess as “Makerphone,” comes from a Kickstarter project. The accompanying video will give you an impression of Ringo.
 
Ringo Kickstarter video

Experiments with radio

Whoever once wanted to develop a Verizon CDMA device had to bring many hundreds of thousands of dollars and a lot of patience. And the often (insanely complicated) certification processes reliably deterred small companies. In the course of the last few years, the situation has been simplified in so far as certification is usually no longer required for LTE and Co. Nevertheless, the components to be used remain problematic. Anyone who has ever dealt with the (considerable) demands of a smartphone SOC knows immediately that this is a major hurdle.
 
No matter whether one approaches the topic of mobile radio out of pure interest, because of its technical peculiarity, or simply for the fun of it, the cell phone kit developed by CircuitMess is in any case a tool that promises joy. I was provided with a sample by Elektor, and in the following you will be able to read about my experiences with it.

What is in it?

The basic architecture is an ESP32, which cooperates with a more or less finished PCI-like module with an SIM800 network processor. This results in a very limited mobile phone support: more than GPRS is not available. Unfortunately, in some countries 2G networks will be deactivated in the not too distant future. But don’t worry. Not only in Europe, this will still take some time, because 3G will be switched off first (and replaced by 5G) due to the poorer voice quality, so GSM will remain available to us for several years in most parts of the world.
 
Be that as it may, the packaging alone is interesting. One is confronted with a molded foam surface in a box (Figure 1), in which the individual modules are fitted. As so often in modern times, there is no printed construction manual. It is available on the Internet instead.
 
Inside the Ringo kit
Figure 1: All parts of the kit are nicely in place. (Source: CircuitMess)
From a technical point of view, the Ringo is otherwise a well-equipped device. The ESP32 can access an external memory in the form of a micro SD card. A color 1.8" display with a resolution of 160 x 128 pixels is available for the display.

In addition to a normal T9 keyboard, a really small joystick is also provided for interaction with the user. In the area of ​​network communication, Ringo offers both telephony and the ability to send and receive SMS. The Ringo’s audio equipment is good. Unfortunately, the buttons on the individual keys are not printed. Not nice, but the usual block of 12 should be pretty self-explanatory. There is also a group of RGB LEDs on the back of the board. 

Assembly!

If you read the documentation and think about the fact that the manufacturer describes the kit as suitable for 11-year-olds, you quickly realize that something is wrong here. The solution to the riddle: The board is pre-equipped with SMDs, and you only have to solder in wired components — so you don’t have to order a reflow oven right away. 

In my opinion, the construction of the kit is almost foolproof. In this context, I found it interesting that a number of circuit boards are prevented by a kind of “spacer” from touching a neighboring circuit board, producing a short circuit. The development team showed attention to detail with the boards used. For example, pads or “soldering eyes” are only provided on one side of the in-house ESP32 board, while the opposite side is completely covered with paint (Figure 2). This precautionary measure prevents accidentally incorrectly soldering the headers, or at least makes it very difficult.

 
One of the Ringo's surfaces
Figure 2: One surface of the board is completely covered with varnish, so you can hardly solder in the headers the wrong way round.
The pin headers used are of very high quality — I wonder why they weren't cut to the correct length. I was less impressed by the fact that two spacers were different, but only slightly, because they were almost the same size. This can lead to confusion, especially with inexperienced young electronics engineers. Also, I don't understand why the spacers had to be screwed together and why 3D-printed spacers were not included.

I was not so happy that some large circuit boards such as the ESP32 are only held in place by a screw (see Figure 3). This leads to the fact that not only I, but especially inexperienced solderers in particular, solder the circuit board at an angle as shown here. The manufacturer has apparently already priced in something like this, because my Ringo was easy to assemble despite this inconvenience.

 
The second circuit board
Figure 3: The second circuit board is on top of it. I've placed the header at a slight angle, but the whole thing still works without problems.
Ringo controls
Figure 4: These are the controls and connections
of the completely assembled Ringo. (Source: CircuitMess).
Another rather minor point of criticism is that the manual recommends installing the circuit boards first and then installing the buttons. This is unfavorable in that some buttons are close to the boards, which makes attaching them a mechanical fiddling. Figure 4 shows the finished mobile phone including the labeling of the operating elements.

The front and back walls consist of a two-part, laser-cut plastic sheet — a very interesting approach. I liked that so much that I will probably do the same in future projects of my own. The bottom line is that assembling the Ringo is a very interesting exercise, during which you can learn a lot about mechanical and other construction. Real problems with soldering are not to be expected from my point of view.

First start-up

After the successful assembly of the somewhat large do-it-yourself phone, press the Power button to wake up the built-in ESP32. At this point, you will probably be prompted to charge the phone. For this purpose, the kit includes a charger with a Micro-USB connector. If you have a modern smartphone, Its charging cable with USB-C plug does not fit.

A micro-sized SIM card is required. A nano-SIM card common today is too small and only fits with such a small subframe. If you are looking for SIM cards for IoT applications, you are not well advised to go hunting in the supermarket or cell phone store. For some years now, there have been dedicated providers for the IoT, such as podGROUP, which — with low data consumption — can offer much lower prices (in the range of €2 to €3 per month and SIM).
 
As the ESP32 is too weak to run a full operating system, you have to be careful when modifying the software. If you write a new sketch into the ESP32 SoC with the Arduino IDE, you eliminate the firmware on it, which provides the various phone functions.
The more elegant way is to set up the toolchain based on PlatformIO, which then allows the firmware to be adapted. Similar to a classic RTOS, all modules are put into a .bin file at compile time, which is then executed.
 
By the way, the firmware provided by CircuitMess is not only suitable as operating software. If you study it carefully, you will learn a trick or two about system programming.

Will Ringo replace your phone?

Can Ringo make your smartphone unemployed? The answer is a more than resolute “no” for many reasons. A modern smartphone can simply do far too much that Ringo can't, and it has several orders of magnitude more processing power.
 
Nevertheless, Ringo is a kit that you will have a lot of fun assembling, and you will certainly learn a lot in the process. The architecture realized here is also suitable for creating various special-interest communication systems.

The firmware of the ESP32 is — if programmed correctly — much more compact than a full operating system like Android. Provided that the radio module is only ever supplied with encrypted information via its interface, a smartphone can be constructed that is virtually invulnerable to many attack scenarios. And that is a strong advantage for some applications.
 
If I were 15 years younger, I would think of many more things for which such a homemade cell phone could be used (except for "posing"). In any case, Ringo is a kit that I really liked putting together.