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Using the IO-16 with relays.


Quantum Bricklet
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Hi everyone,

 

I'm seeking advice on the best way to switch a set of small electric motors (they don't need to be steppers) (each 1.5-4.5 volts  - with a listed typical current 3.50 mA) using the IO-16 bricklet.

Just in case it's relevant they will just be switched on and off momentarily at a time. Not kept on in a running mode.

 

Correct me if I'm wrong but I think I understand for various reasons it's not a good idea to try and power these directly from the IO bricklet so I'm wondering whether to go with a set of 5 Volt reed relays

Nominal coil voltage: 5Vdc

Pull-in voltage: 3.75Vdc max.

http://www.maplin.co.uk/p/5v-single-pole-dil-reed-relay-fx88v 

 

or an all in one relay circuit like this 5V 8 channel relay module board:

http://www.banggood.com/5V-8-Channel-Relay-Module-Board-For-Arduino-PIC-AVR-DSP-ARM-p-74110.html?currency=GBP&utm_source=google&utm_medium=shopping&utm_content=miko_ruby&utm_campaign=Electronic-xie-uk&gclid=CL_lrbiS57sCFabLtAod_CkAZA

 

I need to keep things simple for now as I'm entirely new to this so a part of me says just connect up the IO-16 bricklet directly to the reed relays.  I know the actual voltage from the IO brick is only 4.5 but  as the pull-in voltage of the relay is 3.75 I'm assuming this will be fine.

 

Unfortunately my current knowledge of electric circuits is limited to Ohms

law so using this very basic knowledge and the specs for the relay am I right in thinking I can just connect these up without any additional components just by plugging these into a board and running some very short wires to the relays from each IO output ?

 

I think this is ok if I switch one relay at a time but is it ok if I switch maybe 3 or 4 at once ? Obviously I will use an external power source for the current being switched by the relays - that's not my concern)

 

Alternatively - should I use something like the 8 channel relay board.  It's much cheaper than a whole lot of individual reed relays if I need say 15 or more relays but I feel I'm out of my depth with this at the moment as I couldn't find any information on just how to use the board.  Could it possibly be as simple as connecting a power supply to the board and then power the on board relays by connecting up the IO outputs to the relays on the board ? 

 

Two final questions. If I went with the board option could I split the 16 outputs from the IO bricklet between 2 relay boards. (Each relay board only has 8 relays so I would need to do this)

 

 

If I go with the reed relay option do I need to worry about impedence and fit resistors into the circuit ? (I don't want to do this if it is unavoidable.  As I said - I want to keep things simple for now)

 

Thanks for any help.

 

ps: I haven't bought any bricks or bricklets yet but I think the whole idea is brilliant. I've never felt confident enough to try any projects of this sort before but this seems a great way to experiment and learn at the same time.  Being able to use your favourite code is great too.

 

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Hi Quantum,

 

regarding the switching of external devices you have to consider two things: The necessary voltage and current.

 

Your chosen DIL relays have a coil resistance of 500 Ohms, this will lead to 9mA per Relay when powering it with 4.5 Volts (U=R*I). The absolute maximum Current per pin is 20mA. So this should work.

 

I haven't found an electrical specification of the relay module board. On the picture there seem to be some kind of photocouplers at the input of the module. The question is how high the necessary current is to drive these. Since it is intended to be used with an Arduino I would assume that it will work, too.

 

Two final questions. If I went with the board option could I split the 16 outputs from the IO bricklet between 2 relay boards. (Each relay board only has 8 relays so I would need to do this)

You could. I would assume that every relay (photocoupler) input can be controlled by attaching GND and one output of the IO-16. If you drive the IO-16 output high the LED inside the photocoupler will lid up and the relay will be switched. Additionally you will have to attach power to the relays.

 

If I go with the reed relay option do I need to worry about impedence and fit resistors into the circuit ? (I don't want to do this if it is unavoidable.  As I said - I want to keep things simple for now)
As I have calculated before you should be able to switch the relays directly.
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