Confused about I/O Pins on Axon

[Mastermime]

Hi everyone,

This is supposed to add on to the 'Do I Need Resistors' topic.  Its not allowing me to post on that topic so I'm adding this one.

Individual I/O pins can supply about ~20mA power, each. Exceeding this number could damage/fry the I/O pin.

I don't understand how this is true.  How could a servo be powered if this is true?  I believe I am looking at it wrong.  If someone could explain, Id greatly appreciate it.

Thanks

[superfly501]

I/O pins don't power the Servo, they only give the PWM signal to tell the servo where to move, so you don't need much current for that. You would power your servo through your power source, such as batteries. Some batteries can provide up to a several amps or more. You might have to regulate your power source.

[Mastermime]

Oh ok I understand.  Thank you.  So it would be fine if I powered my 12v LEDS that draw 1 amp using the unregulated section of the Axon II?  The 12 volts being supplied would be a flat 12 volts because it is being supplied from a DC-DC converter.

[superfly501]

I've never used Axon II before, but I'm guessing you mean you have a 12V DC power source that is regulated to the 3.3 or 5V for the Axon II? Then I don't see any reason why you can't connect the 12V LEDs directly to the 12V source.

[jkerns]

Oh ok I understand.  Thank you.  So it would be fine if I powered my 12v LEDS that draw 1 amp using the unregulated section of the Axon II?  The 12 volts being supplied would be a flat 12 volts because it is being supplied from a DC-DC converter.

OK - Servos - those have three wires. Two carry power and come directly from your power supply. And the third is a low current signal wire that gets a pulse signal from the Axon - the Axon does not supply  or sink the power - that's  why you can controll the servo directly from a low power digital output.

LEDs - these have two wires. All the current has to go through whatever is switching the LED on and off. If you connect your LED between power and the Axon the Axon would be trying to control the full amp. That is not a good thing.

If you want to control a 1 amp LED (or DC motor, or...) from a device that can only source / sink 20 milliamps, you need to use some kind of power switching device (relay, transistor) that is controlled by the Axon and will be able to handle the 1 amp from the LED.

[Mastermime]

oh I understand.  I've got to be honest.  I'm not too experience with directly using transistors.  Quite embarrassing.  I understand what is I need too do, but I just dont know how to do it.  I know transistors can act as a signal switch and it can amplify a signal, but that's about all I know.

[Webbot]

Look at MOSFET transistors. In simple terms these are like a relay or electronic switch- ie an output pin from your Axon can turn it on or off but the current just goes via the other pins (not the Axon). Sending a PWM signal allows you to turn the LEDs on/off in quick succession - like a dimmer switch.

[Mastermime]

Thank you for the explanation Webbot.  That really cleared things up for me.  That is easier than I thought.

Btw:  Thank you for Webbotlib project designer also.  Life saver

[superfly501]

My bad then, so it's bad to connect the 12V LED's to the source? I thought having a voltage regulator circuit would protect the axon. So the MOSFET switch would protect the axon, not just act as a LED switch?

[jkerns]

My bad then, so it's bad to connect the 12V LED's to the source? I thought having a voltage regulator circuit would protect the axon. So the MOSFET switch would protect the axon, not just act as a LED switch?

It's bad to connect high current LEDs directly to the digitial output pins of the Axon.

A voltage regulator regulates voltage. It's the high current (greater than 20ma per the spec) that will do in the Axon.

The MOSFET will act as a high current switch to turn the LED on and off as commanded by the low current output of the Axon

[superfly501]

Oh okay, I must have misread what you were saying then.