1
\$\begingroup\$

I have a 3v3 SPI bus with a SDcard on it. I would like to know visually when data is being written to the card. Are there any potential problems with adding a small (1206) SMD LED in parallel as an indicator?

\$\endgroup\$
1
  • 1
    \$\begingroup\$ If you control the bus, then implement the led on your own MCU. If not, what about just on the Chip-Select line? \$\endgroup\$
    – Passerby
    Jul 28, 2016 at 21:33

1 Answer 1

1
\$\begingroup\$

the problems about your idea:

  • a SPI bus runs fast, so if you connect a LED to the data signals or chip select you will not see anything .. its to fast for your eye.

  • the led need some current, the spi pins have to drive the current for it.

a solution could be to use the chip select signal with a transistor to trigger a pulse element with drive a led for a short time.

\$\endgroup\$
3
  • \$\begingroup\$ That is good to identify when data is written or read. Ligthing the LED only for writes (as it seems written in the question) would be much more complex, though. But maybe the question was simply missing that point. \$\endgroup\$
    – dim
    Jul 28, 2016 at 21:59
  • \$\begingroup\$ true, if only on write actions the LED should flash you have definitively to control the LED from your SPI Master Device \$\endgroup\$
    – twooBeers
    Jul 28, 2016 at 22:12
  • \$\begingroup\$ "you will not see anything" - not true, if the write takes long enough you will see the LED at varying levels of brightness. (You still won't see it flicker on and off several million times a second) \$\endgroup\$
    – user253751
    Jul 28, 2016 at 23:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.