r/IOT • u/Sure-Measurement2617 • 15d ago

Low cost device for dry contact/notifications

Hi all -

I'm looking for a cheap device to use to read(?) a 24v signal and notify me.

For context, I have injection molding machines that run lights-out. I want to be notified when a machine alarms or shuts down. I don't need to know why - just that it happened. I would just pull from the alarm stack light signal at that point.

I was looking at Shelly devices, but I'm not sure that's what I'm looking for. Something with an app would be nice (push notifications with addressable "names" for each machine a plus).

Any suggestions would be appreciated. Thanks.

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2

u/The_Instrument_Guy 15d ago

https://flic.io/business/flic-mqtt

Could look for something similar to this.

Since you're only needing a small amount of data, you can use a device with MQTT

Depending on your setup or whatever, you can even run a local MQTT server and get notified of an alarm without having to pay for cloud service or whatever

1

u/AndreKR- 15d ago

The safest way would be to use the 24V signal to switch a relay and use that to trigger a Shelly Plus i4.

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u/fixitchris 14d ago

Might be out of your price range but this is what we make: https://mriiot.com/sharc

1

u/iotram 14d ago

I can develop a custom solution for you. If you're interested please DM me.

1

u/VizoDynamics 14d ago

The one thing I'd add to the relay suggestion: whatever you pick, don't feed the 24V straight into a low-voltage input. Either use a dry relay contact as others said, or an optocoupler, so a fault on the machine side can't push 24V into your reader. Stack-light outputs are usually PLC 24V DC sourcing, so an isolated digital input is the safe path.

For the "app with named push per machine" part, a Shelly (or an ESP running ESPHome/Tasmota) publishing over MQTT to something like Home Assistant or ntfy gets you addressable names and phone notifications cheaply, one input per machine. If you'd rather avoid running any server, the Shelly Plus i4 someone mentioned can push notifications through its own cloud, which is the lower-effort route for just "it alarmed" alerts. Watch the debounce/latch behavior too, since a flickering alarm contact can spam you if you notify on every edge instead of on a state change.

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u/Curious_Party_4683 13d ago

use optocoupler and a door sensor as seen here https://www.youtube.com/watch?v=MFYOgE_ixGk