September 23, 2016
The concept was to put a 32 bit ARM into an Arduino style setup. The "Maple" sounds was designed to have the same physical dimensions and some degree of pin compatibility with the Arduino. What a great idea! Why didn't it fly? It looked like this:
Later they came out with the sleek little "maple_mini", which abandoned physical compatibility with the Arduino, but retained the Maple IDE development system. It looked like this:
The observant reader will have noticed that the original Maple used an STM32 with a larger package (with 64 pins) than what was used for the Maple-mini (48 pins). Both the Maple mini and the Chinese "blue pills" I have been working with use the STM32 with the smaller 48 pin package.
The "made in China" STM32F103 "blue pill" boards I am working with have a lot in common with the Maple Mini, but there are differences. The Maple boards have a boot button rather than two jumpers. The boot "button" on the maple-mini is connected to PB8, and there is a USB disconnect circuit controlled by PB9. On the big maple, the boot button is connected to PC9 and the USB disconnect is on PC12.
The Maple basically put the STM32F103 into an Arduino Pro form factor, giving some compatibility with Arduino shields and such. Along with the Arduino style IDE, it certainly looks like a superior choice to me from this point far in the future, but all we can do is shed a tear. The first boards were sold in 2009, the r5 was being sold in 2010.
It can be powered from USB, from a barrel jack, or from a Li-ion battery. A jumper needs to be placed on the appropriate pair of pins according to the power source. Up to 12 volts can be supplied via the barrel jack, but closer to 3.3 will allow more current without thermal issues with the on-board regulators. The onboard regulators are MCP1703 from Microchip. These have an 0.625 volt dropout (so when your Li-ion battery drops to 3.925, it is game over)
The board can charge the Li-ion batter (that is what the BQ24010 is all about). It works like so:
Maples Rev 3 and Rev 5 also have a built-in LiPo battery charger. In order to use it, put a jumper across the CHRG header on the power selection header and across the USB, or EXT selectors, depending on whether you’re charging the battery via USB cable or barrel jack connector. The LED labeled CHRG will light up while the battery is being charged. When the battery is finished charging, the LED labeled DONE will light up.Why isn't this fine board a winner instead of the Arduino with its wretched 8-bit AVR controller? I don't know what the original price on these were. But I think it boils down to the Arduino being "good enough" and having more publicity. In 2020, I can buy an Arduino Uno for $22 on Amazon with its 16 Mhz 8 bit AVR on board with 32k of flash and 2k of ram. I see an old listing for the Maple at $32. No battery managment on the Arduino either. It just doesn't make sense.
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