Temperature sensor evaluation board for Arduino Nano. Custom PTAT cell and dual-slope ADC design. The PTAT cell features breakaway design of the temperature sense area for remote measurement. Final error after calibration was less than 5%.
Circuit and layout drawn in Altium 17.0.
Revision 1 Errata
Updated Dec 13, 2016
- R8 should pull up to VCC3V3 for stability, not VCC5V which is not well regulated and prone to noise.
- U1 pins 2, 4, and 6 (base) should be shorted together. The current design only connects pins 4 and 6, which results in half the expected PTAT current.
- A 100 ohm resistor should be put across J20 for stability of VREF.
- Pad size for C5 is too small for most 1uF film capacitors. Suggest to change to 1210 footprint.
- Jumpers have 0402 footprint, which have pads that do not short well with manual solder rework. Suggest to change to 0805 or 1206 footprint. Alternatively populate with 0402 0 ohm resistors.
- Add a 4k7 ohm pull up resistor to VCC5V on Arduino pin 12 for one-wire parasitic power.
Linearity is very good. There is a constant offset error, which can be removed through calibration.
Python Plotter Script
The included Python script
plotter.py allows for a realtime graph of temperature values. It also logs all values to a txt file.