I just received a rev 3 maple mini. Has a darker print than the others I've recieved in the past. On VIN it says MAX 5v. But the documentation and previous versions have said I can run up to 12v. I'm a bit worried about plugging in my 9v power source. Will it be ok?
Maple mini - MAX 5V?
(18 posts) (6 voices)-
Posted 3 years ago #
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I got it frm seeeduino
It. says r3 on the unit. they had 80 units in stock. http://www.seeedstudio.com/depot/maple-mini-p-861.html?cPath=132_137. image is different to the unit.Posted 3 years ago # -
gbulmer
Moderatorasterix - The constraint is the voltage regulator. This regulates the voltage down to 3.3V from whatever you put into it. It acts like a variable resistor, and converts the excess power into heat, and it has a limited ability to get rid of the heat. If the heat can't be removed fast enough, it will overheat and, if you are lucky, shut itself down (and come back on when it has cooled enough), or be damaged.
AFAIK, the change to the silk screen is because several people damaged the voltage regulator, but the regulator has not changed.
The link provided by ala42 is to LeafLabs statement that that voltage regulator can dissipate 0.37W maximum (it should be a Microchip MCP1703), when running at an ambient temperature of 25C.
You might want to be conservative, allow a bit of headroom, or a warmer environment and derate it to 0.3W, which represents an ambient of roughly 50C.
So it you use a 9V power supply, it will have to convert the power to heat, and it must not be driven above, say 300mW, so
power = voltage * current, and it must be < 300mW
= (9-3.3) * current = 5.7V * current < 300mW
current < 52.6mALooking at the ST Micro datasheet for the STM32F103xB (i.e. the generic part on the Maple Mini),
(At http://www.st.com/internet/mcu/product/189782.jsp, document DS5319: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00161566.pdf)Section "5.3.5 Supply current characteristics" says the maximum current, running at 72MHz, when "All I/O pins are in input mode".
50mA = "Table 13. Maximum current consumption in Run mode, code with data processing running from Flash" with "External clock(2), all peripherals enabled" "All I/O pins are in input mode" at 85C.
36mA = "Table 17. Typical current consumption in Run mode, code with data processing running from Flash" with "External clock", "All peripherals enabled (though it says add 0.8mA for each ADC)" "All I/O pins are in input mode" at 25C.Note these values are with all pins set to be digital inputs, and tied to ground or Vdd, so they are not driving any current, not even the pin 13 LED.
Bottom line, a Microchip MCP1703 regulator *should* run from 9V, providing the MCU isn't driving much current (WAG <10mA) through output pins.
A better approach would be to use a 5V power supply. Doing the power calculation again
(5-3.3) * current < 300mW
1.7 * current < 300mW
current < 176mA(NB: If that regulator is one of the other common SOT23 parts, then its maximum power dissipation might be even lower, and hence its safe current supply capability lower.)
(FULL DISCLOSURE: I am NOT a member of LeafLabs staff).
Posted 3 years ago # -
jessb
LeafLabsHey guys,
gbulmer is, as usual, totally correct; the power regulation on Maple Mini r3 is the same as r2, but "officially" from now on it only supports up to 5V. As before you should still be able to power it from higher voltages as long as you're not pulling too much current, according to the calculations gbulmer provided.
And no, it's not a knock off, seeed is an official LeafLabs distributor! Boards should be trickling back into stock at other distributors in the next couple weeks.
(Also woops, sorry for not pushing the updated docs into the repo. will do that asap.)
Posted 3 years ago # -
Thanks gbulmer. You're always very helpful and explain things quite well.
Although afaik now I have yet another blown board!!!!- I powered up the unit using 9v external battery. Unity worked fine.
- I patched in my xbee (vcc, gnd, rx2,tx2), and array of shiftbrite leds (spi pins in maple, v+ & gnd to the same battery powering the maple) and uploaded a sketch via usb power (no external power)
- The first shiftbrite led in my shiftbrite array lit up!!! That has never happened before using usb power! For that to light up I must be getting 7.2v out of the VIN rail or the shiftbrite won't light up. Im pretty sure this shouldn't be happening.
- Each shiftbrite chip draws up to 800ma. So rather than pushing my luck I disconnected usb and powered up the units using external power (9v).
- Everything appeared to be working ok. Xbee receiving data, lights on in my shiftbrite array. I disconnected the xbee and shiftbrite array to upload any sketches.
- I changed to a new rechargable battery (multi reads the battery at closer to 10v).
- Had everything completely disconnected (including spi pins)
- vin & gnd to battery and SMOKEY VREG!!!!!I don't know seriously I've blown too many of these boards, I've spent probably close to $600 on maples with postage added in, and I'm a bit deflated right now.
Posted 3 years ago #
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