pin caracteristics

[steve24rdg]

Hi
Can anyone tell me if an output is switched from high to low whether or not in the low state it can be used to sink current or if I need to use a dedicated earth.

Example

I have a small solenoid that needs to have its polarity changed depending on whether its position is extended or retracted.
If I can toggle 2 pins from either high to low it would be a much easier circuit than sharing an earth.

thanks

 

[hippy]

Yes, an I/O pin can sink and source current so you could use one resistor and two LED's in opposite direction across a pair of I/O and then light one or the other by setting one HIGH the other LOW.

The current sourced or sunk is limited though, 25mA max, and a solenoid may require more current than that. Go over the limit and you risk burning an I/O out whether sinking or sourcing, could even permanently destroy the chip.

 

[steve24rdg]

Thanks hippy
Yes I imagine a solenoid would require more current in was planning to use transistors
Steve

 

[erco]

Use 2 pins and an H-bridge.

Low current HG7881 or L9110S, moderate current L298N, all under $2 on Ebay China. Not sure if you can use a flyback diode across the solenoid coil since you're reversing though.

 

[steve24rdg]

Erco thanks for the info.
I sometimes see a small ceramic capacitor across to 2 poles on electric motors. I presume this is used in place of a flyback diode. Perhaps I could do the same with a solenoid?