u/Afraid_Loss5187

Hi everyone,

I’m designing a small wrist-worn device with a heater that contacts the skin. I need to measure/control the heater surface temperature using a contact temperature sensor fixed to the heater, possibly with thermal paste. I want to use it in the medical area, so it should be precise and accurate

Available sensors include LM35, DS18B20, DS1821, and SHT35, but I’m also considering NTC thermistors or Pt1000.

Which sensor would you recommend for accurate and safe skin-contact heater control? Any advice on mounting, response time, and safety cutoff design would be appreciated.

I have this 100k NTC thermistor (shown in the attached photo) but it doesn't have any clear branding or part numbers on it.

I need to figure out its specific type so I can find its coefficients (Beta value / Steinhart-Hart parameters) for my project code.

A few quick details: - Nominal resistance: 100k ohms at room temperature.

Application: to read the temperature using esp32 s3 mini.

Does anyone recognize the specific manufacturer, form factor, or model? If not, what is the most common default Beta value for this specific style (e.g., B3950, B4250)? Thanks in advance for the help!

https://preview.redd.it/ymj52lmkqb1h1.jpg?width=4244&format=pjpg&auto=webp&s=1c74c9f76ba2152095393fa3ac42817d28fc8304

https://preview.redd.it/5eolabllqb1h1.jpg?width=3420&format=pjpg&auto=webp&s=7a8d848f4d027704d69dd04e2465cb7488425c58

Hey everyone, having a weird issue combining modules on an ESP32.

My Setup:

Keypad: 4x4 Matrix via I2C expander on GPIO 16 (SDA) and 17 (SCL).

RFID: Two RC522 readers sharing default VSPI pins: SCK (18), MISO (19), MOSI (23).

Reader 1 Control: SDA/CS (5), RST (27).

Reader 2 Control: SDA/CS (14), RST (13).

Power: Everything (both RFIDs + I2C expander) is powered from the ESP32 3.3V pin. Esp is powered from usb.

The Problem

Individually, everything works perfectly fine. However, when combined together, the RFID readers stop working completely. Now, when I go back to test just a single RFID reader on its own, it looks like one of them isn't responding or working at all anymore.

Is this a 3.3V power/current limit issue from the ESP32 regulator, a hidden pin conflict, or am I hitting the infamous RC522 MISO line-hogging bug where the inactive reader crashes the SPI data bus? Any advice on how to fix this is appreciated!

I made a high-side switch to control 12V power to an L298N motor driver using an ESP32/Arduino GPIO pin. I want to know if my design is correct and why my MOSFETs keep getting damaged.(i tested on breadboard, one got damaged one worked. the worked one got damaged later. being careful to work quickly and let each leg cool before soldering the next one to avoid heat damage)

**Goal:**

Control 12V supply to L298N using a 3.3V or 5V GPIO pin from ESP32/Arduino.

Is this circuit design correct for switching 12V with a 3.3V/5V GPIO?

P-Channel MOSFET high-side switch circuit. Components: IRF9Z24N or F4905S P-channel MOSFET , 2N2222 NPN transistor, 10kΩ resistor.
12V supply connects to MOSFET Source. 10kΩ pullup resistor connects between MOSFET Gate and Source (12V). 2N2222 Collector connects to MOSFET Gate. 2N2222 Emitter connects to GND.
I didnt add 1kΩ resistor between GPIO input pin and 2N2222 Base. MOSFET Drain is the switched 12V output. All GNDs are common.

https://preview.redd.it/ybxdwes6i3yg1.png?width=922&format=png&auto=webp&s=3826720be5581935e051ac3a1b3ca6794684b8d5