Friday 8 February 2013

Custard Pi 1 - Protection layer for the Raspberry Pi

Wanting to encourage young people into electronics I decided to provide a number of resources for the Raspberry Pi. The Custard Pi 1 - Protection layer for the Raspberry Pi is the first of these.


The Raspberry Pi GPIO allows the control of external electronics. There are two rows of 13 pins which are brought out to a 26 way header on the edge of the board.

However there are a number of points that a user has to take account of when using the GPIO.

There are 6 pins on this connector that nothing should be connected to. If anything is connected to these there is a risk of damage to the Raspberry Pi.

All the pins work to 3.3V logic. Many electronic circuits work to 5V logic or can have even higher voltages. If a user accidentally connects a higher voltage to a 3.3V pin there is a risk of permanent damage to Raspberry Pi.

There are 2 voltage supplies provided on the GPIO, one at 3.3 V and the other at 5 V. However there is limited current availability from these pins and they are not protected from excessive current draw.

Finally, the pins are not labelled on the 26 way GPIO connector.  One has to keep cross referring to the diagram and there is a high risk of a wrong connection and risk of accidental damage.


The Custard Pi 1 provides the following benefits for the hobbyist intending to use the GPIO.

1.   All the pins are protected from accidental connection of a high voltage.

2.    There are screw terminals provided for easy connection to external electronics. These are in groups and labelled.

3.   There are no screw terminal connection to the 6 pins that are not in use.

4.    The 3.3 V and 5 V voltage rails are current limited to 50 mA with a resettable fuse.

5.    The board simply plugs into the 26 way GPIO connector.

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