3 replies to this topic

[Spork]

Hi,

Somebody has probably already asked this, but the keywords are so general ("analog", "pin", "power", "ground") that I haven't been able to find it.

The BlinkM documentation suggests that it can be plugged directly into a 'duino. If so, I guess it would be using A2 and A3 as GND and 3.3V. I think I read elsewhere that the Netduino analog pins come up at 3.3V when it is powered on... Is it safe to have 3.3V to the device's VCC and GND? Would it just mean that the device has no voltage potential to operate, but that it wouldn't smoke and that it would begin operating once the A pin connected to GND is set to 0V?

I'd like to make a little standoff that holds sensors off to the side, away from the minor heat island caused by the Netduino. I want to use a strip/vero board with 8 lines, 6 of which will be connected to A0 through A5. Then, with two jumper wires and three cuts, I can connect the two i2c sensors and one analog sensor, but I'd need to use A2 as a 3.3V supply and A1 as ground. If you've ever seen pirates make somebody "walk the plank", that's what I'm doing with the sensors. Ship = Netduino, plank = strip board, pirates = me.

I've thought about alternatives (e.g. sensors dangling from ribbon connectors) but I really have my heart set on having them walk the plank, if I can, and it all hinges on using A2 as 3.3V device supply and A1 as GND for devices. Any reason not to try this?

[Stefan W.]

Hi,

Somebody has probably already asked this, but the keywords are so general ("analog", "pin", "power", "ground") that I haven't been able to find it.

The BlinkM documentation suggests that it can be plugged directly into a 'duino. If so, I guess it would be using A2 and A3 as GND and 3.3V. I think I read elsewhere that the Netduino analog pins come up at 3.3V when it is powered on... Is it safe to have 3.3V to the device's VCC and GND? Would it just mean that the device has no voltage potential to operate, but that it wouldn't smoke and that it would begin operating once the A pin connected to GND is set to 0V?

I'd like to make a little standoff that holds sensors off to the side, away from the minor heat island caused by the Netduino. I want to use a strip/vero board with 8 lines, 6 of which will be connected to A0 through A5. Then, with two jumper wires and three cuts, I can connect the two i2c sensors and one analog sensor, but I'd need to use A2 as a 3.3V supply and A1 as ground. If you've ever seen pirates make somebody "walk the plank", that's what I'm doing with the sensors. Ship = Netduino, plank = strip board, pirates = me.

I've thought about alternatives (e.g. sensors dangling from ribbon connectors) but I really have my heart set on having them walk the plank, if I can, and it all hinges on using A2 as 3.3V device supply and A1 as GND for devices. Any reason not to try this?

The device won't smoke, but the netduino will. See http://www.netduino....duino/specs.htm - you're only allowed to draw 2mA per analog pin, your LED will draw more. You'll need to use the "real" 3.3V and ground pins of the netduino.

[Spork]

Thanks for reminding me about the max current per pin. I was using the BlinkM as an example of this having been done before, but maybe it was only done on Arduinos. Instead of an LED, I'll have a BMP085, HIH-4030, and HH10D on the plank. Typical current for each is 650uA, 200uA, and 150uA, respectively. Sum is 1mA. Peak/max current for each is 1000uA, 500uA, and 180uA, respectively. Sum is 1.68mA. So, I think it's reasonable to assume total draw around 1mA with peaks up to 1.68mA, which means I'm good to go?

[Chris Walker]

Hi Spork, Many of the Arduinos can drive quite a bit of current through the digital and analog pins, so several companies built accessories which took advantage of that feature. Unfortunately that's not a particularly good engineering practice I'd recommend using the 3.3V header for power and the GND header for ground--and use the digital and analog headers for digital signals and analog inputs. If you're only using ~2mA of current, then you are technically fine using analog pins 0-3. And analog pins 4-5 can drive ~8mA of current. But I'd still recommend using the power headers for power... Chris