DS18S20 | GUILCOR SENSORS

DS18S20
Temperature sensors

Compact 1‑Wire sensor with high accuracy, ideal for embedded systems, HVAC, and remote temperature monitoring.

Maximum precision
+/- 0,50°K

Minimum temperature
-55°C

Maximum temperature
+125°C

Minimum dimensions
4 x 6 x 27

Response time
Fast

Self-heating
Low

Price
Low

Drift
Low

What is a DS18S20 sensor ?

The DS18S20 is a 1-Wire digital temperature sensor developed by Maxim Integrated, preceding the DS18B20 but still widely used in embedded systems.

It offers high accuracy, low power consumption, and full compatibility with existing 1-Wire networks and libraries.

It is ideal for projects requiring:

a reliable measurement,
minimal wiring,
and long-lasting performance without recalibration.

Operating principle

The DS18S20 converts the measured analog temperature into a 9-bit digital value, transmitted via the 1-Wire protocol.

Each bit corresponds to 0.5 °C, and the raw value is directly converted to degrees Celsius as follows:

T (°C) = Raw value / 2

The sensor is powered conventionally (3 wires) or in parasitic mode (2 wires).

Technical specifications

Parameter	Typical Value
Measurement range	−55 °C → +125 °C
Typical accuracy	±0,5 K (−10 → +85 °C)
Resolution	9 bits (0,5 °C)
Conversion time	750 ms
Nutrition	3.0 → 5.5 V or parasitic mode
Interface	1-Wire Digital
Unique identifier	Hermetic axial glass
Typical current	1 to 2 s in the air

Wiring configuration

Type	Description	Precision
2-wire	Simple assembly, sufficient for short measurements.	✅ Standard
3-wire	Reduces the influence of cables.	🏆 Industrial
Integrated (stuck)	Often soldered on transistor, module, or heatsink.	💡 Thermoprotection

Self-heating

The KTY81-110 generates very little heat (≈ 0.5 °C/mW in air and 0.1 °C/mW in oil).

Its low power dissipation ensures accurate measurement, even in confined environments.

Application areas

⚙️ Thermal surveillance of electric motors and windings

🔋 Battery and charger protection

💻 Sensors integrated into power modules (MOSFET, IGBT)

🚗 Temperature measurement in automotive embedded systems

🧠 Thermal regulation for precision electronics

Should I choose a DS18S20 sensor ?

Strengths points

⚡ Simplicity and total compatibility
→ Works with all existing 1-Wire systems (Arduino libraries, ESP32, Raspberry, etc.) plug-and-play, no complex setup required.
🎯 Stable precision without recalibration
→ Factory calibrated, the DS18S20 maintains a precision of ±0.5 K and exceptional long-term stability, with no maintenance required.
🔋 Ideal for low power consumption systems
→ Its parasitic mode with 2 wires allows it to be powered without a dedicated VDD, perfect for battery-operated applications or in hard-to-reach areas.

Weaknesses points

📉 Fixed resolution at 9 bits
→ No precision adjustment possible: each step is worth 0.5 °C, limiting measurement accuracy.
⏱️ Conversion a bit slow
→ A complete conversion takes about 750 ms, which may be too slow for fast closed-loop measurements.
🔗 Less efficient than the DS18B20
→ The DS18S20, although robust, is now replaced by the DS18B20, which is more flexible (12-bit resolution and improved calibration).

Useful information

Here is some useful information regarding the DS18S20 sensors.

Resolution and precision

The DS18S20 offers a fixed resolution of 9 bits, with a step of 0.5 °C.

Its accuracy is comparable to that of the DS18B20 within the useful range, but its internal ADC does not allow for an increase in resolution.

Resolution	No measurement (°C)	Conversion time	Typical accuracy (−10 → +85 °C)	Extended measurement range
9 bits (fixe)	0,5 °C	750 ms	±0,5 K	−55 °C → +125 °C

🔹 Remarks:

Each binary step corresponds to 0.5 °C, encoded on a signed 16-bit word.
The drift is very low (< ±0.2 K/year), and the sensor is factory pre-calibrated.
No configuration required: the reading is always done in 9 bits.

Example of application – Reading equation of a DS18S20

The DS18S20 returns a signed 16-bit raw value.

The temperature conversion equation is simple:

T(°C) : Raw Value / 16

🔹 Example 1 – Positive Reading

The sensor returns:

LSB = 0x50
MSB = 0x05

Valeur brute = 0x0550 = 1360₁₀

T = 1360 / 2 = 680 °C

❌ (Unrealistic — let's take a correct case 🙂)

LSB = 0x50
MSB = 0x00

Raw value 0x0050 = 80₁₀ T = 80 / 2 = 40,0 °C

✅ Result: measured temperature = 40.0 °C

🔹 Example 2 – Negative temperature

The sensor returns:

LSB = 0x90
MSB = 0xFF

Raw value (two's complement):

Raw value 0x0550 = 1360₁₀ T = 1360 / 2 = 680 °C

✅ Result: measured temperature = −56 °C (lower limit of the sensor).

🔹 Practical notes:

The reading is done via the "Read Scratchpad" command (0xBE).
The temperature value is stored in bytes 0 and 1 of the scratchpad.
The sensor also includes high/low alarm values (TH, TL) and a CRC for validation.

Integration diagram in an electronic system

The DS18S20 connects exactly like the DS18B20, via a 1-Wire bus.

It operates in 3-wire mode (VDD, DATA, GND) or in parasite mode (2 wires: DATA + GND).

🔹 Typical components

Component	Fonction
DS18S20	1-Wire Digital Sensor
Pull resistance 4.7 kΩ	Maintains the DATA line in a high state
Microcontroller (Arduino, ESP32, Raspberry Pi)	1-Wire Bus Master
Power Supply 3.3 V / 5 V	Source (or parasite mode)
Shielded cable (if >10 m)	Noise reduction

🔹 Functional diagram (ASCII)

Classic 3-wire mode

+3.3V / +5V │ [4.7kΩ] │ DATA ────┼──────────────┐ │ │ GND DS18S20 │ GND

Parasitic mode (2 wires)

DATA ───┬────────────── DS18S20 │ GND

🔹 Operating Principle

1️⃣ The master (microcontroller) sends a 1-Wire reset pulse.

2️⃣ The sensor responds with its presence (presence pulse).

3️⃣ A "Convert T" command (0x44) initiates the temperature conversion.

4️⃣ After ~750 ms, the data is read via "Read Scratchpad" (0xBE).

Multi-point advantage – Unique ID 64 bits

Each DS18S20 has a unique 64-bit address composed of:

8 bits: family code (0x10 for DS18S20)
48 bits: individual serial number
8 bits: CRC check

This system guarantees:

🔗 The connection of multiple sensors on the same line (multi-drop).
🧠 Reliable individual identification, even after replacement.
🧩 Simplified maintenance on extensive networks (IoT systems, HVAC, data loggers).

Example of a unique address:

10-2C-11-6B-46-08-00-3F

✅ This allows each probe to be queried independently without collision on the bus.