Using SPI and PWM with Arduino UNO

Using Arduino Networking, Protocols, and Devices
#1

I'm working on a project that requires 6 PWM pins to control two RGB LEDs. However, I also need to be able to communicate with the Arduino via SPI.

I've read that in order to use the SPI pins for other functions as well as SPI you need a >1K resistor between the pin and the load. This wouldn't allow for enough current to power the LED, though.

Is this only a conflict during communication or all the time?

I'm new to working with SPI so wondering if anyone with more experience has any insight on this.

Thank you!

#2

I've read that in order to use the SPI pins for other functions as well as SPI you need a >1K resistor between the pin and the load.

This is bullshit. You can use the pins for either function but not for both. There may be special circumstances where such a cheap hack works but it's definitely no general solution that works with every setup and every SPI device. You may have to change the hardware. A Mega2560 helps.

#3

pyfi:
I've read that in order to use the SPI pins for other functions as well as SPI you need a >1K resistor between the pin and the load. This wouldn't allow for enough current to power the LED, though.

You don't need to use pin 10 for SPI as it is just used for SS. Any I/O pin can be used for that - but pin 10 must be set as OUTPUT.

That just leaves pin 11 with a potential dual role for PWM and SPI. As pin 11 is MOSI and normally drives the SPI device at 5v I suspect the device would suffer no harm from receiving a 5v PWM signal. However using a 1k resistor may help. You can locate the resistor so that it protects the SPI device without interfering with the flow of current between pin 11 and the LED.

...R

#4