Raspberry Pi GPIO Control

Gary Stewart wrote:

That is not what is specified by the maker of the relay board. They clearly state that each driver input needs 15 to 20 mA.

And everything you read on the Internet is true.......Do as you will.  It also clearly states that it is equipped with a high current relay (AC 250V at 10A, DC 20V 10A), but says nothing about whether the board can handle AC (traces, isolation, etc.) and not only that, I would never use a product that is not UL listed for AC use, or approved by another similar certifying body.  So if you decide to do that as well, up your house insurance policy.   I only use the board for DC applications and have a separate 30amp UL approved relay to operate AC appliances with my pi, and all my wiring, fuses, AC inlet/outlet connectors, etc. are UL certified and meet National Electric Code requirements for selection and how everything is connected together.

Mark Beckett wrote:

Your observations are more in line with what I expected.

Your method using a transistor (with series resistor between GPIO pin and base ....for those others reading this) is the perfect solution.

In addition to the base resistor (2.2k), I also put a 10k resistor between each GPIO pin and ground.  I specifically have chosen GPIO pins that are INPUTS and in a LOW condition at boot (most, but not all pins are, and also not in the same state at boot depending on what Model B Revision board you are using), however they are floating and can accidentally trip the relay card inputs.  I have seen where other users have experienced this.  The 10k resistor guarantees a LOW at boot, critical in my application anyway.

Some use a UNL2803 instead of a transistor, a darlington pair being way overkill working with such low current/voltage, but in the long run I guess you save money on some of the parts (transistors, resistors, etc.) and it makes wiring a bit easier. 

Gary Stewart wrote:

That is not what is specified by the maker of the relay board. They clearly state that each driver input needs 15 to 20 mA.

And everything you read on the Internet is true.......Do as you will.  It also clearly states that it is equipped with a high current relay (AC 250V at 10A, DC 20V 10A), but says nothing about whether the board can handle AC (traces, isolation, etc.) and not only that, I would never use a product that is not UL listed for AC use, or approved by another similar certifying body.  So if you decide to do that as well, up your house insurance policy.   I only use the board for DC applications and have a separate 30amp UL approved relay to operate AC appliances with my pi, and all my wiring, fuses, AC inlet/outlet connectors, etc. are UL certified and meet National Electric Code requirements for selection and how everything is connected together.

Mark Beckett wrote:

Your observations are more in line with what I expected.

Your method using a transistor (with series resistor between GPIO pin and base ....for those others reading this) is the perfect solution.

In addition to the base resistor (2.2k), I also put a 10k resistor between each GPIO pin and ground.  I specifically have chosen GPIO pins that are INPUTS and in a LOW condition at boot (most, but not all pins are, and also not in the same state at boot depending on what Model B Revision board you are using), however they are floating and can accidentally trip the relay card inputs.  I have seen where other users have experienced this.  The 10k resistor guarantees a LOW at boot, critical in my application anyway.

Some use a UNL2803 instead of a transistor, a darlington pair being way overkill working with such low current/voltage, but in the long run I guess you save money on some of the parts (transistors, resistors, etc.) and it makes wiring a bit easier.