Arduino Uno + 2x 8 channel relay modules or better 16 channel module?

Hey all,

I read through some threads but I´m still not sure how to finish my project. First of all I need to say that I´m a noob and I just started working with arduino uno.

My project:

I´d like to control 15 different channels with the arduino uno http://www.arduino.org/products/boards/arduino-uno

Some people said I better use 2x 8 channel relay module like http://www.sainsmart.com/8-channel-dc-5v-relay-module-for-arduino-pic-arm-dsp-avr-msp430-ttl-logic.html

and some talked about the 16 channel module http://www.sainsmart.com/relay-1/relays/16-channel-12v-relay-module-for-pic-arm-avr-dsp-arduino-msp430-ttl-logic.html

Are there any advantages or disadvantages? Do I need to change the analog inputs to outputs at both relay modules? Or is there any other way to solve it?

I hope someone can help me here.

Thanks,

Mare00

It depends on what type of load you'll be controlling. If controlling AC loads or high current, inductive DC loads, it's best to use opto-isolation.

The 8 relay modules can be configured to use its optoisolators, but the 16 relay module cannot (problem is with the schematic and PCB).

To save on required pins, could use a shift register like the 74HC595 to control the relays.

Hi, No matter how many relays you have you will need a separate supply to power the relay coils, the arduino 5V will not be able to provide the necessary current.

Tom.... :)

dlloyd: It depends on what type of load you'll be controlling. If controlling AC loads or high current, inductive DC loads, it's best to use opto-isolation.

The 8 relay modules can be configured to use its optoisolators, but the 16 relay module cannot (problem is with the schematic and PCB).

To save on required pins, could use a shift register like the 74HC595 to control the relays.

Thanks for your fast reply. I´m controlling some low voltage circuit with a few mA. Nothing inductive.

I read about the shift register too. I will need two of the 74HC595 to control 15 "buttons". But that shouldnt be a problem.

TomGeorge: Hi, No matter how many relays you have you will need a separate supply to power the relay coils, the arduino 5V will not be able to provide the necessary current.

Tom.... :)

Yes, I know. Thats not a problem at all.

I think I will use 2 shift registers and transistors to control the 15 buttons. I just need to close 15 buttons without any heavy load at all.

Thanks for all help.