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Hardware Lesson


#1

Can someone explain this for me:

“27 GPIO-6 Association STATUS, 24mA drive, 3.3V tolerant LED, Weak pull down”

what does the weak pull down mean? This is in relation to hooking an LED up to this:

http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=25_65&products_id=527

Unlike the WiFly shield this breakout does not have onboard LED support so I pondered adding it, but my electronics is basic so I need educating.


#2

Hi Lloyd

Some processors give you an option on the gpio pins when configured as outputs,

Weak pullups are normally high value resistors built into the port that can either pull the pin to ground (pulldown) or pull the pin to 3.3v (pullup). Some times when interfacing to other devices ie… push buttons the value will return to 3.3v or ground when you let go…

It just means YOU don’t have to…

An LED will probably be extremely dull if used with weak pullups as, like I said, they are high value resistors @ 20k or so. You need about 470 ohm to light an LED…
Putting a 470 ohm pullup with the weak pullup selected won’t change the output current much but if you do connect a 470 ohm via an LED you really don’t need the weak pullup.

Does that help?

Cheers Ian