Limit Switches and Sensors

Hi everyone,
I am working in a project where I want to automate a small production line using Node-RED, but I have no idea what are the limit switches and sensors that works perfectly with Node-RED, Any suggestions?

Welcome to node red.

What hardware are you planning to run node red on? How are you going to connect the switches? Wire them directly to whatever is running node red or via a bus of some sort?
How critical are the limit switches? Is there a safety or damage issue if node red does not see the switch correctly?

A bit more information on which sensors you are thinking about would be useful as there are numerous types of sensors.
e.g. Temperature, humidity, pressure, light, sound, magnetic, infra-red, ultrasonic - to name a few.

A number of people on this forum use Wemos devices (ESP8266 WiFi-enabled microcontrollers) to sense and control things as they are inexpensive compared with a RPi, so if you damage a Wemos during your experiments it's not a 'show stopper'. The data can be sent via MQTT (a lightweight transmission protocol) to a RPi to do the processing in Node-RED.

If you flash the Wemos with firmware like ESP-Easy, Tasmota or Platformio you have access to drives/libraries for all sorts of sensors.

It’s a prototype, and for now a laptop will be used to run Node-RED.
What I am looking for are switches and sensors that provide IoT, so it can be easily connected to Node-RED. Also there is no safety or damages if sometimes it fails.
Do you have any recommendations?

The sensors are going to be used to detect plastic objects and others to detect liquid level. Whereas the switches are going to be used to give signals to pneumatic pistons.
And I really appreciate the information you are sharing.

I'll have to think about how to detect plastic objects.

It might be possible to detect liquid levels with a light-beam, assuming the liquid-container is transparent.
Alternatively, it might be possible to use an ultrasonic distance measuring device positioned over the top of the liquid container.

Have you tried Googling this as I'm sure it is a common problem in the process control industry ??

There are quite a few industrial control people on the forum who might jump in to this thread.


As limit switches and actuators are quite time critical I think you should find a way to connect then directly to your Laptop via USB as the good old parallel printer port is not available any more. You can use a usb capable microcontroller or a dedicated chip:

I think any wireless solution would bring to much unpredictable latency.


Our main detection types were Optical (beam break and reflective), Capacitive and Inductive. If the process is 'clean' or the object very light then Air may not be such a good idea, but can be used elsewhere. All these sensors in their various forms can be connected to a digital input, either on something like the Wemos/ESP style modules, Arduino, RPi etc..

If safety was required, we would use a make and break pair of switches, or a couple of seperate switches, preferably changeover with again, one switch making and the other breaking (in case a PSU goes down or a wire breaks).

At the end of the day, there are many choices out there and your choice will basically depend upon how much you want to spend and how safe you need it.

If your use for the switches , sensors etc. is of life critical importance then most definitely stay away from hobbyist stuff, while they "look and feel" like real equipment quite often they are the production runs that didn't meet the production spec's and got dumped on the market. While they work, they aren't up to the quality spec's of the company. I think this was alluded to above but I'm going to repeat this. Go to the big name distributors and pay the price, there is a reason for that. Mouser and Digikey are two names in North America that deal in good quality parts, don't know where you are. If safety isn't an issue there is a ton of parts out there that would work. You will find many opinions in here on what people think is good or will work and I'm sure that they probably will.

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I have to agree with Gerry, if you are monitoring/controlling anything mechanised then safety is critical for both equipment and personnel protection, you should check what sort of compliance you have to legally design for in your sector/locale. In the UK we have the EU Machinery Directive 2006 for example. Critical production industrial plant environments simply do not allow simple passive switched outputs to be used, sensors are all loop driven(4-20mA) or have a digital interface that can verify the status of the sensor (is it active/is it healthy). Again for control applications wireless connections should be avoided at all times.

There are plenty of multichannel analog I/O interfaces around which will connect to a pi via serial modbus/MQTT over ethernet etc. Analog loops will travel 100's of meters. You will find the sensor types you are looking to integrate come std with 4-20mA and serial outputs.

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opto22 has some pretty cool equip and talks about using node-red. I would take a look.

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Used it on a lot of automation projects. Support is excellent and their Software easy to use. Stability of the devices themselves top notch!

That is very true. I did our water coop control system. No issues is over 15 years.

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