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#1 CasaDelGato

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Posted 11 December 2010 - 01:57 AM

Has anyone actually run a Netduino mini on 12v, and used 8 or so digital outputs? (I also notice that it's only kinda-sorta BS2 compatible, as the outputs have far lower drive capacities.) I'm wondering since it uses a standard LDO regulator, and has no heatsinking. It really looks like it will easily overheat.

#2 Chris Walker

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Posted 11 December 2010 - 04:19 AM

Hi CasaDelGato, Generally speaking, we recommend using the digital outputs to drive digital signals (PWM, SPI, UARTs, etc.) rather than driving LEDs or such directly. I'm not sure which you're doing...but if you're worried about max current then you might want to use transistors to drive higher-current components. That said, you should have no problem driving 8 or more digital signals. The power regulators are 800mA, so unless you're using a ton of current they should run pretty cool. As far as voltage, we recommend using 7.5V to 9V on VIN (although we support up to 12V). If you want to reduce heat further, you can supply 5V to pin 21 instead. The Netduino Mini is pin compatible with the BASIC Stamp 2--but it is a bit different electrical signal-wise. It's digital pins are 5V tolerant, but its 32-bit micro drives 3.3V signals. Some other notes on the Netduino Mini: its four PWM lines are in the same position as those used on the BASIC Stamp BOE boards (and they're true hardware PWM--so you can run all four "in the background"). And it has 4 true analog inputs (pins 5-8) which can accurately measure inputs from 0-3.3V DC. Plus it has built-in UART, I2C, and SPI...so you get a ton of features in a tiny package. Chris

#3 CasaDelGato

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Posted 11 December 2010 - 05:07 AM

That said, you should have no problem driving 8 or more digital signals. The power regulators are 800mA, so unless you're using a ton of current they should run pretty cool.

Except you appear to be using the SOIC-8 pin package for the reg, which is tiny and has rotten heat dissipation. With no heat sink, there is absolutely NO way you can draw anywhere near 800ma without frying it.
Has anyone even run it at 100ma/12V to see if it gets hot?

The reason I'm asking is that we have a BS2 driven board, but a BS2 isn't really capable of the processing we need now. So we are looking for something that can plug into a BS2 socket instead of a BS2. Since the hardware already exists, it's supply is 12v, and some of the outputs drive LED's.

#4 Chris Walker

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Posted 11 December 2010 - 05:20 AM

Except you appear to be using the SOIC-8 pin package for the reg, which is tiny and has rotten heat dissipation. With no heat sink, there is absolutely NO way you can draw anywhere near 800ma without frying it.
Has anyone even run it at 100ma/12V to see if it gets hot?

The reason I'm asking is that we have a BS2 driven board, but a BS2 isn't really capable of the processing we need now. So we are looking for something that can plug into a BS2 socket instead of a BS2. Since the hardware already exists, it's supply is 12v, and some of the outputs drive LED's.


Hi CasaDelGato,

The Netduino's microcontroller itself can only drive about 200mA, and the 16 GPIOs are limited to about 120mA total... Combined with the microcontroller's power consumption, you might see around 200mA or so of total consumption with the pins driving max current.

While the power regulators are 800mA we don't recommend drawing that much current (especially with a 12V-20V VIN power input). But in our testing we really haven't seen any heat issues with the LDO power regulators. Yes, we are space constrained so we can't use power regulators with big heat sinks--but for most applications they seem to work well.

On our test jigs, we drive 12 LEDs simultaneously using 9V power and have never had heat issues... But then again we don't drive them for hours on end and we aren't dropping down from 12V.

Chris




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