Sensor Forum - Recent Threads

RE: Batteryless temperature sensor

DAB — Thu, 11 Jun 2026 19:16:03 GMT

I agree, flat cable would be the way to go.

Batteryless temperature sensor

obones — Wed, 10 Jun 2026 09:13:53 GMT

I have a fridge with two compartments, one for "fridge" temperature elements, and one for frozen foods.

As it's showing its age, I want to monitor the temperature in both parts to be sure everything is still edible.

For the fridge part, placing a zigbee sensor powered by a 2xAA or CR2032 battery is actually working fine, the battery is not too weakened by the 2°C temperature and the metallic body plates are not attenuating the signal too much.

For the frozen foods parts, it's a bit more complex as temperatures go as low as -25°C. On top of that, because the thermostat is is in the fridge part, it happened in the past that the compressor never turned on because the temperature in the garage where it is located reached 4°C, effectively within the thermostat set temperature.

As a result, I wanted to both have a quick way to check the current temperature, while having a history of said temperatures and to get this, I installed a zigbee sensor with a wired temperature probe like this:

This works fine but the probe cable is quite thick (3mm) leading to air leakage at the location where the cable is getting through the door seal.

Using a small scalpel, I was able to strip the outer insulation to get access to the three inner cables which are way thinner, hoping this would restore the seal effectiveness.

Sadly, while this is better, this is still not enough, ice is building up inside, starting along the three cables as can be seen here:

I had removed most of it two days before taking this picture and it's already back.

So now, I'm trying to figure out an alternative for this and NFC/RFID came to mind as this would allow to get a sensor without batteries getting frozen inside the compartment, thus not requiring any wire to get into it and thus no longer interfering with the seal function.

With the appropriate search terms, I stumbled across this reference design from TI: https://www.ti.com/tool/TIDM-RF430-TEMPSENSE

But this gets me even more questions:

What cost for creating this board?
What tool to program the MCU? and what cost for this tool?
What to use to read back the temperature? I have RPI Pico W or ESP32 at hand for the wifi communication.
Would reading work through the metal sides of the fridge?
Would this work if the sensor is at 90° with respect to the reader?

For the last question, this stems from the fact that if question 4 answer is "no", then the RF waves would need to work through the 1/2 cm gap left by the compressed seal when the door is closed, as seen here:

From what I grasped reading various articles, the longer the distance between the RFID tag and the reader, the larger the reader's antenna would need to be. I even saw 60cm diameter antennas, which, well, won't fit here at all.

Do you think this RFID/NFC tag idea is worth exploring? Or would you suggest an alternative like cold resistant batteries if that exists?

Thanks for your insights.

RE: Batteryless temperature sensor

obones — Thu, 11 Jun 2026 07:55:21 GMT

Indeed, but in my case, it only goes to the fridge compartment, not the frozen food one. That one does not have auto defrost.

RE: Batteryless temperature sensor

Gough Lui — Thu, 11 Jun 2026 07:37:30 GMT

If you want very thin wires, perhaps try a thermocouple bead to an external reader circuit or meter? You might need some special covering to make it truly air-tight (otherwise you will have frosting issues).

- Gough

RE: Batteryless temperature sensor

dougw — Thu, 11 Jun 2026 02:19:46 GMT

NFC could work, although I haven't tried this specific application.

I did however do a battery-less temperature sensor using RFID frequency to transfer power - see Klingmagon.

RE: Batteryless temperature sensor

beacon_dave — Wed, 10 Jun 2026 16:15:24 GMT

[quote userid="121623" url="~/technologies/sensor-technology/f/forum/57026/batteryless-temperature-sensor/236066"]Note that this is a working fridge with a slight auto defrost issue.[/quote]

Quite often the auto defrost fridges have a drain hole. I think it leads to a drip tray under the unit rather than just dripping onto the floor. Perhaps there is already an existing route through this drain ?

RE: Batteryless temperature sensor

BigG — Wed, 10 Jun 2026 14:15:21 GMT

There is a new(ish) RFID tech that's on the market, which technically could work. It's called RAIN.

https://therainalliance.org/what-is-rain/

However, it may be too expensive for the hobbyist market. I am not sure myself.

RE: Batteryless temperature sensor

michaelkellett — Wed, 10 Jun 2026 09:49:41 GMT

I can suggest two alternatives - both of which I use.

1) Use thermocouples with thin wires - OK with most seals.

2) Use pretty much any kind of sensor and drill a hole though the side of the fridge.

These suggestions are not made lightly - I have evidence:

Drilled hole in the side of fridge - sealed around two thermistor wires with bubble wrap. Note that this is a working fridge with a slight auto defrost issue.

The sensors - one is for the fridge in general and one for the load - no load at the moment so they are both just resting on the floor.

The fridge controller - the display is telling me that the F(ridge) temperature is 6.5 and the L(oad) temperature is 6.0. (Warm because I just had the door open for a minute or two to take pictures.

The controller display cycles and also shows the ambient and compressor temperatures and if the compressor is on or off.

I modified the fridge and made the controller for a job about 10 years ago but now I just use the fridge to keep my cheese and butter cool and my mint sauce frozen.

Drilling fridge walls is easy - usually very thin layer of metal or plastic sheet on each side of insulating foam.

Check out what's in the Steam Controller

stanto — Thu, 30 Apr 2026 22:43:21 GMT

[View:https://www.youtube.com/watch?v=hVRfie61QyE:640:360]

Capacitive touch, fancy joysticks, buttons and touchpads. There's even an infrared LED. Valve went all out.

I think the best part about it is that it's easily repairable. 7 torx screws and you're in!

where can I buy Snap connection electrode in mumbai.

manojroy123 — Sat, 07 Mar 2026 13:13:46 GMT

Where Can I buy snap connection electrode in mumbai. Bellow is the given electrode link. I wan't to solder it on PCB. Please share some link.

https://www.cngoochain.com/product/electrode-pin-to-snap-connect-adapters-tens-lead-wire-adapters-2mm-pin-to-35mm-39mm-snap-connector.html

Please also check the link bellow.

www.sparkfun.com/myoware-2-0-muscle-sensor.html

RE: where can I buy Snap connection electrode in mumbai.

rsjawale24 — Sun, 08 Mar 2026 15:50:21 GMT

Go to Lamington road in Mumbai and show the photo to any of the shops, they will guide you on which shop stocks the part.

RE: where can I buy Snap connection electrode in mumbai.

manojroy123 — Sun, 08 Mar 2026 05:50:57 GMT

Thanks I like the rivet system of using the clothing Pin. Very helpful of you of sharing the information.

RE: where can I buy Snap connection electrode in mumbai.

shabaz — Sat, 07 Mar 2026 19:06:31 GMT

Any local clothing repair/sewing store should be able to provide those. Normally sewn or riveted, but could probably be soldered with some effort.

Exploring Sensor Technology Applications in Real-World Projects – Glad to Join the Community

nickcarlo — Fri, 30 Jan 2026 16:00:22 GMT

Hello everyone,

I’m excited to be part of the element14 community and to join discussions around sensor technology. This field has always fascinated me because sensors play a critical role in modern electronics, from simple hobby projects to complex industrial and automotive systems.

I’m particularly interested in how different sensors (motion, proximity, temperature, and pressure sensors) are integrated into real-world applications to improve automation, safety, and user experience. Reading hands-on projects, tutorials, and case studies shared by experienced engineers here is extremely valuable for learning how theory is applied in practical scenarios.

I enjoy experimenting with electronics and embedded systems and often explore how sensor data can be used more efficiently through smart integration with software and connected platforms. Communities like element14 are important because they encourage knowledge sharing, troubleshooting, and innovation across different levels of expertise.

Alongside my interest in hardware and sensors, I also follow technology trends related to automotive systems and smart displays. I recently came across a useful resource related to Android Auto that may be helpful for those interested in in-car technology and media integration.

I’m looking forward to learning from the community, participating in discussions, and sharing insights as I continue exploring sensor-based technologies. Thanks for welcoming me here!

Does anyone know where can I get graphehe powder from house hold item.

manojroy123 — Wed, 28 Jan 2026 15:20:18 GMT

Does anyone know where can I get graphene powder from house hold item. Or maybe I can make graphene at home in small quantities. lts say 1 gram to 10 gram range. I have heard graphene powder has very electrical conductivity. I wan't to test it for copper electroplating.

RE: Does anyone know where can I get graphehe powder from house hold item.

manojroy123 — Wed, 28 Jan 2026 16:20:56 GMT

Conductive ink for copper electroplating. silver and palladium is very expensive. Looking or alternative which is inexpensive and can be product in large quantities.

RE: Does anyone know where can I get graphehe powder from house hold item.

shabaz — Wed, 28 Jan 2026 16:04:05 GMT

There was a BBC article that discussed household objects, but it might take you a few years to collect enough: https://www.bbc.co.uk/news/science-environment-11478645

RE: Does anyone know where can I get graphehe powder from house hold item.

HKPhysicist — Wed, 28 Jan 2026 16:01:44 GMT

It is just a newly discovered carbon crystal. Why do you need it?

You can tear it apart from an house hood pencil tip with sticky tape and see it under Electron Microscope; but what is your purpose?

RE: Does anyone know where can I get graphehe powder from house hold item.

dougw — Wed, 28 Jan 2026 15:39:35 GMT

I don't know of any household products that use graphene powder.

You can buy graphene powder on Amazon.

It is definitely highly conductive.

RE: Does anyone know where can I get graphehe powder from house hold item.

vmate — Wed, 28 Jan 2026 15:26:36 GMT

You will definitely not get graphene powder from any sort of household item, or be able to create it yourself in any way. You can get graphite powder maybe, but not graphene.

RE: How to detect vehicle sound at 100 m distance using microphone and Arduino?

heinej — Tue, 23 Sep 2025 07:41:54 GMT

Any vehicle? So the former "clap switch" for cars?

Some time ago, I had to computationally compensate a continuous strain gauge load cell in the ton range
against interference from approaching/passing trucks and forklifts. One should certainly consider a geophone or array microphone or MEMS microphone with digital signal processing
in one (at least two microphones (differential sound)).
In my case, it was a supplementary accelerometer (deep earth vibrations, Sub 5Hz) on the subframe
that enabled precise detection of interfering trucks.
Although the questions above exclusively concern signal conditioning, I would first use standard measurement equipment to understand the physics and acoustic facts, and then consider amplifying, targeted filtering.

I would have thought that vehicle-specific characteristic audio patterns would be discussed here first, Short-Time Discrete Fourier Transform (STDFT), and FFT, and object approaching speed determination using the Doppler effect?

How to detect vehicle sound at 100 m distance using microphone and Arduino?

abhishekks — Fri, 19 Sep 2025 05:47:51 GMT

Hello everyone,

I am working on a project where I need to detect the sound of vehicles (cars, heavy trucks) from a distance of around 100 m. The microphone will be placed in an open area on land, and the goal is to identify when a vehicle is approaching.

Currently, I am evaluating microphones like AOM-5024L-HD-R and CMA-4544PF-W, connected to a MAX9814 preamplifier module, with the output fed into an Arduino Uno ADC.

My questions are:

What type of microphone is most suitable for long-distance vehicle detection (100 m)?
How can I calculate whether the microphone output voltage will be sufficient for reliable detection at that distance?
Should I use additional filters (e.g., low-pass or band-pass) to separate vehicle sound from background noise (wind, people, etc.)?
Would I need a higher-gain preamplifier or a different approach (like a geophone or array microphone) for better detection?

Any advice, references, or design suggestions will be very helpful.

RE: How to detect vehicle sound at 100 m distance using microphone and Arduino?

abhishekks — Tue, 23 Sep 2025 07:25:03 GMT

first phase of the project is to get some voltage level when any vehicle moving towards mic.

RE: How to detect vehicle sound at 100 m distance using microphone and Arduino?

abhishekks — Tue, 23 Sep 2025 07:23:34 GMT

yes

RE: How to detect vehicle sound at 100 m distance using microphone and Arduino?

heinej — Tue, 23 Sep 2025 07:20:03 GMT

Is it a real-time application?