More powah

Hello once again Arduino community,

I'm designing a system to automate the manufacture of space telescope optics, and I'd very much like to incorporate an Arduino into my design.

Long story short, I basically want to know if it is possible to draw 70mA of current from a pin. I suspect it is because I've driven servos off the pins that I suspect draw much more then that. At the same time the specs for the duemilanove say that it can deliver only 40mA per pin.

So I'm left wondering -- what kind of current draw is safe for the Arduino? If it any help I would be drawing 70mA from at most 6 pins off and on for at most a couple hours at a time.

Thanks

what kind of current draw is safe for the Arduino?

30mA would be safe. Anything over 40mA produces damage. Plus a total of about 150mA for all pins combined.

If you need more you use transistors or FETs .

I suspect it is because I've driven servos off the pins that I suspect draw much more then that.

I suspect you've controlled a servo off a pin, but not powered one.

You make an important distinction Grumpy_Mike (also, pardon my word salad in that sentence you quoted). I should modify my statement to be "in the past I have used the pins to generate a waveform to control a servo". Does this mean that the current that actually powers the servo is drawn not off the Atmega pin, but straight of the USB bus through that 5V pin?

With this knowledge, could I not do something similar and power my solenoids off the 5V pin and connect all the grounds to pins on the Atmega? I've worked with 8051's in the past where instead of doing this I used a buffer chip as a current sink. Would this be a better solution?

Thanks for the help

With this knowledge, could I not do something similar and power my solenoids off the 5V pin and connect all the grounds to pins on the Atmega? I've worked with 8051's in the past where instead of doing this I used a buffer chip as a current sink. Would this be a better solution?

Note unless the solenoids draw less then 40ma each, 30ma or less is better. In that case the current would flow from +5vdc to the solenoid and on to a digital output pin, so the pin current limit still applies. The output pin current limit is the same no matter if it's sourcing current (HIGH output) or sinking current (LOW output).

Lefty

With this knowledge, could I not do something similar and power my solenoids off the 5V pin and connect all the grounds to pins on the Atmega? I've worked with 8051's in the past where instead of doing this I used a buffer chip as a current sink. Would this be a better solution?

A buffer chip as a current sink would be a better solution. Typically a solenoid driver like a ULN2803 is used.

There are some interfacing ideas here for what you want to do:

http://ruggedcircuits.com/html/circuit_ideas.html#HighI

http://www.ruggedcircuits.com

With this knowledge, could I not do something similar and power my solenoids off the 5V pin and connect all the grounds to pins on the Atmega?

An important knowledge concept to adapt to early is that the arduino power supply is mainly for powering the arduino and providing logic level signals to external gizmos, and generally not for powering the external gizmos themselves.