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The ELM331 is a complete temperature measurement and control system in an 8 pin package.

This integrated circuit is designed to compare two resistances and drive an output pin depending on the relative value of each. Typically, one of the resistors will be an NTC thermistor, and the other one will be a temperature independent resistor (whether fixed or variable). When the magnitude of the resistance connected to pin 2 exceeds the value of the resistance connected to pin 3, the output pin will be driven to a high state. Hysteresis maintains the output in that state until the relative values differ by approximately 8% (or typically 2°C for a 10KΩ thermistor).

To reduce the possibility of sporadic outputs, a condition must exist for three successive cycles, or 6 seconds, before the output pin can change state.


  • Primary thermostat in temperature control systems
  • Staging control for auxiliary heating or cooling installations
  • Under or over temperature alarms


  • Low power CMOS design – typically 1mA at 5V
  • Wide supply range – 3.0 to 5.5 volt operation
  • Built-in proportional hysteresis
  • Measurement in progress output
  • Time delay on operate improves noise immunity
  • Internal pullup resistor on the reset input
  • High current drive outputs – up to 25 mA

Connection Diagram

( PDIP or SOIC, top view )
ELM331 connection diagram

Block Diagram

ELM331 block diagram


The ELM331 data sheet (ver B, 29K):

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Quantity Pricing

The following are the unit prices, as you vary the quantity purchased:






All prices are in Canadian dollars. We use the total number purchased (ELM331P + ELM331SM) for the calculation.


Select the desired integrated circuit package type, then the quantity desired, before adding it to your shopping cart. Quantity discounts will be applied as appropriate.

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