dulllou

原帖由 funghome 於 2009-6-6 12:01 發表
analogWrite(pin, i);=PWM????

http://arduino.cc/en/Reference/AnalogWrite

pupil

原帖由 edwardfcy 於 2009-6-6 12:42 發表
但係佢最大可接受的Sink-current是幾大？接多幾粒是否可以加Open-drain line driver IC就OK呢？

一般來說, mcu i/o pins sink 嘅能力(current)係強過 source 嘅能力, 所以 sink design 係好 d. 如果 current 大, 當然要 driving circuit 喇. 一般 i/o pins 都係幾十 mA.

dulllou

原帖由 edwardfcy 於 2009-6-6 12:42 發表
但係佢最大可接受的Sink-current是幾大？接多幾粒是否可以加Open-drain line driver IC就OK呢？

You can sink 60mA at 25C and get down to a voltage of 1.5v.

That means sinking current you will not get the full 5v across the load but 5 - 1.5 = 3.5v

Sinking 40mA gets you down to under 1V on the output where as 20mA gets the output voltage down to 0.5v

pupil

原帖由 dulllou 於 2009-6-6 17:10 發表


You can sink 60mA at 25C and get down to a voltage of 1.5v.

That means sinking current you will not get the full 5v across the load but 5 - 1.5 = 3.5v

Sinking 40mA gets you down to under 1V on the ...

The graphs on the datasheet show the above figures, BUT
the ABSOLUTE MAX DC Current per I/O pin is 40mA only.

[ 本帖最後由 pupil 於 2009-6-6 18:34 編輯 ]

edwardfcy

咁即係要加line driver先可以同時接幾粒LED!

pupil

原帖由 edwardfcy 於 2009-6-6 19:27 發表
咁即係要加line driver先可以同時接幾粒LED!

用粒 transistor (or even darlington) 都得啫, 唔係咩都要 ic 嘅.

edwardfcy

咁咪１粒LED一個３極管，如果切５X 7既 MATRIX咪成12粒Transistor！咁係咪用IC會好D呢？C_HING:funk: :funk:

gulakpi

Very interesting!  

燕飛

原帖由 edwardfcy 於 2009-6-7 01:12 發表
咁咪１粒LED一個３極管，如果切５X 7既 MATRIX咪成12粒Transistor！咁係咪用IC會好D呢？C_HING:funk: :funk:

u may consider the current need

pupil

原帖由 edwardfcy 於 2009-6-7 01:12 發表
咁咪１粒LED一個３極管，如果切５X 7既 MATRIX咪成12粒Transistor！咁係咪用IC會好D呢？C_HING:funk: :funk:

For matrix, you will arrange the LEDs in rows and columns, and 1 transistor for each row/column only.