Difference: RaspiElf (32 vs. 33)

Revision 332018-09-22 - PeterSchmid

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The Raspberry Pi ARM processor supply voltage is 3.3 V and the GPIOs are not 5 V tolerant. The Elf supply voltage is 5 V. This means that the GPIOs (input) has to be protected from Elf. The easiest way is to use diodes e.g. 1N4148 to protect the GPIOs from the 5 V, but the GPIOs need then pullup resistors. Thankfully the Raspi GPIOs have internal pullups and they can be controlled by software. The cathode has to be on the Elf side.

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The Raspberry Pi ARM processor supply voltage is 3.3 V and the GPIOs are not 5 V tolerant. The Elf supply voltage is 5 V. This means that the GPIOs (input) have to be protected from Elf. The easiest way is to use diodes e.g. 1N4148 to protect the GPIOs from the 5 V, but the GPIOs need then pullup resistors. Thankfully the Raspi GPIOs have internal pullups and they can be controlled by software. The cathode has to be on the Elf side.

It is possible that the Elf works with 3.3 V supply voltage, but this is not within the specifications. In this case the diodes are not needed. Connect the Raspi Pin 1 to P4 Pin 3 (do NOT connect Raspi Pin 2!).

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