Blue Spike input specs (non-competiton bot)

Technical Electrical
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Helping my kids redo a T-shirt cannon that had PVC pressure components (non-no). We have some donated pressure switches from SMC that use a PNP output that can handle 80mA max. I want to use one of those to control a compressor on/off via a relay, preferably a blue spike.

I’m trying to figure out what the input parameters are for the Blue Spike Relay module. It’s max control voltage and it’s current requirements. Surprised it’s been hard to find. Anyone know? I found this in one version of an old datasheet:

“Hi: 3V min @ 4mA; Lo: open or ground.”

Which seems at least somewhat ambiguous. I read that as Switch ON with minimum 3V @ 4mA (12mW), and switch off by grounding or leaving Open. But what is the max input voltage and current?

Anyone know any further details on the inputs? My switch will output 11-12VDC.

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The IFI robot controller (flat black rectangle) used a 7.2V backup battery and iirc that was responsible for powering the relays in addition to servos, so 7V would be okay. I want to say I’ve shoved 12V into a spike relay’s input pin and it worked fine, but that was years ago now.

Worst case, you toast the spike and replace it with a $0.80 40A automotive relay and an inline fuse.

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One problem is I can’t find any automotive relays of that switching capacity that have less than 80mA coils. Or I’d just start there.

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Hmmmm

I wonder if there’s some kind of device that lets you use a small current to control a larger current

Hmmmm

I also hate double relays, but sometimes ¯\_(ツ)_/¯

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Here’s a post that identifies the optoisolator in the spike. Use of Arduino to control a Spike Relay - #7 by Jetweb

I’m fairly certain the backup battery was not used for the relay outputs. The manual specifically references it in the PWM section but not relay.

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Yeah, trying to keep it simple component wise. And avoid having to create a PCB to hold them all. Thus the reason to consider the spike. If I’m upping componets I can just stick a voltage regulator in there to drop it. Or I can use a relay to trigger a spike, etc.

But to the OQ, if I can determine the input specs, I don’t have to do any of that. If I had enough spare I’d dissect one to see whats in there. I assume a MOSFET, but just a WAG.

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Thanks Joe. I had seen that post when searching. But it didn’t fit what the Spike datasheet says, or what I think it says anyway. It says 4mA to trigger, and that thread implies it took 65mA although what was taking 65mA (what part of their circuit) wasn’t completely clear. And that referenced datasheet says the max current the internal LED can take is 60mA. But I’m no EE so little fuzzy on those optoisolator details.

Maybe a simple in-series resistor will do.

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As I remember the black spike accepted 12-24V input and could switch 20 amps. Not sure blue is the same.

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Here is the spec sheet from IFI for the blue Spike relay. Team 358 hosts a lot of old FRC resources on their website. http://team358.org/files/programming/ControlSystem2009-/spike-blue-guide-sep05_PLUS.pdf

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@Wednesday Henry, thanks, but that is the spec sheet I copied from in the original post. It is incomplete on specs. Thus the question.

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For posterity if anyone else finds this thread…

Well, I hadn’t considered the spike wasn’t potted. It popped right open and I could see what’s inside. Optoisolators as others had said, and the (complete) datasheets for those are readily available. I was a little surprised it had a dual mechanical relay that the Optoisolaters triggered; I was expecting some kind of SSR.

So seeing that all I needed to do was control the current to the Opto’s LED, I used a 2.4k resistor in line with the 11.8V source and held it to right at 5mA (+/- depending on actual battery levels) and the optoisolator switched the relay just fine at that small current. Also cut the resistance to 1.2k and doubled the current, also worked fine. Well below the 60mA limit of the diode.

So as long as the compressor doesn’t blow the 20A fuse the spike will work perfectly with my pressure switch’s PNP output (with a current limiting resistor).

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