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so I did a little research on this but the answer to my particular problem did not exist.

I have a data logger shield created by deek robot (deek-robot.com) which seems pretty similar to adafruits data logger shield so I assume they would use the same pins, about this one I can research and find the pins.

but in case of the sensor shield I could not find anything specially since there is no reference on the manufacturer on the board and only referred to as "Arduino Sensor Shield V5.0",as this is a shield for sensors and has almost every pin available on it I would assume it can use most of the data pins and depends on which pins I connect.

Now my question is that can I use these shields together if I want to use those digital pins already used by the data logger? or I can use them together only if I leave out the digital pins 10 to 13 out of use on my sensor shield? sensor shield v5.0 Right-side pins Left-side pins

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The 'data logging' shield by Adafruit and Deek Robot has two devices.

First device is the SD card which uses SPI bus. Every SPI device on the SPI bus has to have a select pin CS. On this shield the SD card has pin 10 as the CS pins.

The second device on the data logger shield is a RTC clock. The RTC clock is on the I2C bus.

So the data logger shield uses the I2C pins, the SPI pins and a pin for CS. Arduino in Uno and Mega R3 form factor have the SPI as a 2x3 header and the I2C pins SDA and SCL are last two pins on the header near the USB connector.

On Uno the data logging shield uses pin 10 as CS, 11, 12, 13 as SPI and A4, A5 as I2C.

If you have the version of the data logging shield which can be used on boards other than Uno, then:

  • On Mega it uses pin 10 as CS, 50, 51, 52 as SPI and 20, 21 as I2C.
  • On Leonardo it uses pin 10 as CS, 2, 3 as I2C (and the SPI pins which are only on the SPI header).
  • On Arduino Zero the shield uses pin 10 as CS, 11, 12, 13 as SPI (and the I2c pins are only on the SDA/SCL header).

The 'sensor shield' doesn't have any devices. So it makes no difference in pins usage. With or without the 'sensor shield' if you have the 'data logging' shield attached, you can use only the pins not used by the 'data logging' shield.

Since SPI and I2C are a bus, you can wire additional SPI devices to the SPI pins and additional I2C devices to the I2C pins, but you can't use these pins for anything else if they are configured for the bus.

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  • Ok thanks, a rather thorough answer, I will mark it right away after testing them , but what you indicated seems to be the right answer and even with more details , just another quick and small question, I read that the I2C can be used with as many devices as you want since they don't have CS of their own? this now means I am down to minus 2 analog and minus 4 digital pins, so assuming I hit this cap I will have to use MUXes I suppose
    – Hitman2847
    Mar 12, 2022 at 17:27
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    @Hitman2847, I2C doesn't use CS. the devices on I2C bus have addresses. If you need more pins, switch to Mega, but first check if the 'data logger' shield uses pins 11 to 13 or the 2x3 SPI header and the SDA and SCL pins or the A4 and A5 pins.
    – Juraj
    Mar 12, 2022 at 19:12
  • well the data logger must use the 11 to 13 pins because it only connects physically on the side pins and the 2x3 SPI header is free and not connected to anything
    – Hitman2847
    Mar 14, 2022 at 11:20

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