Resistors with unknown purpose

[sonnytiger]

I understand how the circuit works for the most part (micro controller pulls pin low or high to turn on one or the other led) but I don't get why the 330 ohm resistor is there just sucking up current for what seems like no reason. And it is directly connected across the supply (albeit through the SIP resistor array).

Thanks for any help!

[T3sl4co1l]

Surely you mean to ask if the 150 ohm resistors are there for no apparent reason...??

The 330 ohm resistors are current-limiting the LEDs.  When the MCU pins are high or low, the LED to GND (via 330 ohm) or to VCC (via the other, not shown) lights up.

And, the 150 ohm resistors I believe are there to shunt the LEDs when the MCU pins are tristated, so that the LEDs don't quite light up.  150 seems awfully low for this, but I think that is the purpose.

Tim

[sonnytiger]

yes sorry, the 150 ohm ones

that makes sense, otherwise they would probably dimply light up, eh?

[dom0]

A little bit, yes, eh?

[sonnytiger]

You're not using it right!