Contributed by iiv, curated by Ai-Thinker

A few days ago, while chatting in the group, I happened to get one of Brother Mo's (yes, the guy who calls himself the polyhedron of Happy Planet!) newly invented little boards. It is a very small board using the M62-CBS module that Ai-Thinker released not long ago. This module is tiny, only 12x12mm in size (click here for module details). Based on this module we can build some compact applications. The chip used by this module is our old friend again, the BL616, which performs quite well.

Live look:

The front of the board — the layout is very compact.

The back, where the silkscreen shows the IO markings plus Brother Mo's exclusive logo.

You can see it is a very small board. I measured it at about 25x25mm. Despite its size, it still carries an onboard CH343P UART chip for easy serial debugging, plus an RS2227 that can switch between two USB ports; the switch on the back lets the M62 switch between USB and UART. There is also an onboard common-anode RGB LED and a patch antenna I had never seen before (Brother Mo, are you there? Could you send me a few samples to play with! I don't know why thinking of Brother Mo always makes me think of lucky draws, haha /funny). From the silkscreen on the back you can see a total of 13 usable IO pins are brought out, convenient for building other functions.

It is a really nice board, and I honestly cannot find any faults with it. But Brother Mo asked that I must give some suggestions, and if there are none I have to make them up on the spot. So let me briefly share my personal opinions:

• The RGB LED pin could be changed to keep one set of SD card functions, because the SD card pins happen to be IO10 - IO15
• Replace the RS2227 with a QFN package, since its size is much smaller than the current MSOP, saving some space; then a 0603 or 0402 indicator LED could be placed next to it as a power LED
• I feel the silkscreen on the back is a bit large and misaligned; every time I check a pin I have to count one by one. If it were smaller and closer to the header pins, the pin definitions could be identified at a glance
• If possible, I hope auto-download can be added, so that the reset button doesn't have to be pressed when flashing firmware

Those are my humble opinions on this board. Okay, Brother Mo, don't read any further.

Let's light an LED!

Since the board is still in the testing phase, my board has a bug. I had encountered something similar before, so my guess was that the BOOT pin was not connected to the module. I couldn't help myself and took it apart. Let's take a look at what's inside the module...

There are several 0201 components on this board. To keep them from being blown away, I used high-temperature tape to stick them down (although one resistor still ran off in the end...).

Apply some solder paste, hot air gun at 500 degrees, and it comes off in no time. You can see the test point at the back is connected to IO2 of the internal chip. On some Ai-Thinker modules this pin only connects to this test point. Looking at the schematic (a very blurry schematic; I put on my reading glasses and used a magnifying glass for a long time...), the resistor from IO2 to the module's BOOT pin is not soldered. So when designing boards with Ai-Thinker modules, pay attention to this. I remember making the same mistake the first time I designed a WB2 board; I thought my board was wrong and studied it for a long time, only to find out it was a module issue...

Once the problem is found, it is easy to solve. You can directly fly-wire the test point with enameled wire. But since we've already opened it up, that's obviously not my style. Why not open the lid and see what's inside!

You can see the layout is very compact. In the middle is the BL616 chip from Bouffalo Lab, plus some peripheral components. Find the corresponding resistor position and solder a 0201 0-ohm resistor on it. But I only had 0402, so I used a piece of wire to connect it.

If nothing unexpected happens, our BOOT pin should now work normally. Hold BOOT and plug in USB; the device appears, and it's done.

Finally, light the LED again. Well, goodbye!

Have questions?

For other questions, please visit the unified discussion area: Ai-Thinker Discussions