wireless (passive?) rpm sensor

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I have a rotating shaft and I want to measure its rotation speed by means of a sensor and a phonic wheel . The problem is that this shaft is mounted on another rotating part, so the sensor cannot be wired (rotary joint is not an option).

I searched on google but I was not able to find anything. Do you know if there’s any kind of wireless rotating sensor without battery? or at least with a battery that lasts years. The sensor would transmit about 10 hours per day, so it’s not low duty cycle. The rpm of the shaft is nothing special, about 30 rpm, so the sensor does not need a high frequency input. 12 V DC power source.

(A waterproof system would be better)

In my mind I was thinking about a sensor which could be powered magnetically with the shaft rotation itself. So a kind of passive sensor which transmits to a receiver positioned in the static part of the machine. But since it sounds very fancy, also a battery one could be taken into consideration.

Any idea of a suitable sensor for this application?

edit: I add two youtube videos of a similar application: https://youtu.be/5xqiPsePk8Q

it’s not the same, but let’s think that I need to measure the rotating speed of the shaft which dispenses the plastic film.sensorwirelessproximity-sensorindustrialShareEditFollowFlagedited 3 hours agoasked 3 hours agoVal12144 bronze badges

• I usually stick a little magnet to the motor shaft, and use a cheapy Hall effect sensor to detect the magnet coming and going. No wiring is connected to the magnet, of course. – tlfong01 3 hours ago    
• 1that’s not possible, the shaft is rotating but it’s mounted on another rotating part. – Val 3 hours ago
• OMG, that is unthinkable. Can you give a photo or a sketch? Sort of forarm and back arm? Or explore RFID stuff. – tlfong01 3 hours ago    
• Or use ultra low power WiFi controller ESP32, with both magnet and Hall effect senor on the forarm. – tlfong01 3 hours ago    
• 1i added a video. Consider that I need a commercial off-the-shelf solution, not something DIY style – Val 3 hours ago
• Ah, so seeing is believing the unthinkable. Me IQ97 friendly DIY hobbyist is giving up. Cheers. – tlfong01 3 hours ago   
• 1Be aware that shopping questions are off-topic and will result in your question being closed. You might want to reword your question. – Transistor 3 hours ago
• @tifong01 thanks for trying 🙂 , Transistor what’s the section for such a question? – Val 3 hours ago
• I’d suggest a coin-cell powered, Bluetooth Low Energy, sealed module. Could sense a rotating magnet or optical wheel on the shaft. Relays data to smartphone. But need more details re size, environment, etc. No off the shelf product though, you need a custom design. – Mark Leavitt 1 hour ago 
• Battery will be simplest. Otherwise you could look at wireless charging systems to power your sensor. – Brian Drummond 1 hour ago
• I was afraid I needed a custom designed solution, but I hoped that something was already available. I can go with a battery too, if it lasts long enough. – Val 38 mins ago
• Ah, my suggestion use magnet, Hall effect sensor, WiFi controller which are easily available cheap commercial devices. Now I have one more suggestion, using an reflective optical sensor (TCRT5000), The idea is summarised below: (1) attach a reflective shiny surface on the middle of the forearm, (2) place the optical sensor somewhere on the back arm. (3) Now whenever the forearm turns at an angle that the optical sensor detects a signal from the reflector, it knows one turn is made. The set up is simple. I saw this used in an big industrial plant. / to continue, … – tlfong01 3 mins ago   Edit   
• You might like to watch the video showing the use of the optical sensor to count the breads in a plant.(1) What are the two sensors doing in the automatic bread production line? electronics.stackexchange.com/questions/514448/…. Cheers. – tlfong01 1 min ago   Edit   

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