[FEZ Spider] maxO module Issues

Hello everyone.
I started to face a problem with my maxO modules.
I’m a beginner in this, and I would really appreciate if anybody could light up the path for me a little bit.
Long story short, I’m trying to open some relays whenever I activate certain maxO outputs, and for this to happen, I must connect the maxO ground with the board that has the relays on.
Everything works just fine when I disconnect the ground, but as soon as I connect the ground to the relays, the outputs deactivate. And whenever I disconnect ground off of the whole thing, they stay deactivated.
Would someone please help me out with this? I’d appreciate it so much.

Thank you so much in advance. Have a nice day.


hi mate, can you tell us about your relays? And how you’re powering the relays and the Spider.

This sounds like different ground references. Can you explain what you mean in the above, what state do you NEED to have the GNDs in as your final state, connected or not? And can you confirm that in that state, from startup, whether the behaviour you see is as you expect or not?

PS: others reading this: can you give the original post the thumbs up so we can get over 50 points quickly?

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That’s done !!! Welcome to the forum. :slight_smile:


Hi Brett.
These relays are used to activate certain testing devices on this project.
The relays’ general specifications:

Cynergy DAT70510.
-Coil Specification: 5V
-Insulation across contacts: 10KV
-Switching voltage maximum: 7000V

The way I’m powering the relays is by a 5v power source, and I’m powering the Spider with another power source (12V).

And the GNDs must stay connected as the final state. The thing is that the behavior is variable when the grounds are connected, even from startup, the maxO outputs activate sometimes, and sometimes they don’t. I also noticed that the maxO output voltage decreases when I connect the GNDs (from 3.2V to 2.5V, I’m not sure if that’s a normal thing or if that’s correct).

Thank you so much for reading and answering to this topic.

Thank you Bauland!

Have a nice day!

voltage measurement change like you point out happens when you change the relative ground between two isolated power supplies - measured separately they seem fine, but if you measure GND to GND you’ll see there’s a difference.

If you have to power these things with a joined ground, then you need to plan to do that from the outset. The simplest way would be to take the 12v power and pass it into a regulator to get your 5v for the relay, then everything is starting from the same GND potential. Even an efficient switching regulator like an LM2596 based unit would most likely be fine, for example at AU$2/pop you can use these [url]http://www.ebay.com.au/itm/10-PCS-DC-DC-Buck-Step-Down-Converter-Module-LM2596-Voltage-Regulator-TE097-/262398151961[/url]. The Spider only needs 5v and 3v3, so I’d be considering running appropriate sized regulators for both the relay and two for the Spider from a single higher voltage supply.

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Thank you so much Brett!

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