Using a precision op-amp lets us set the output reference level with a passive network because thermal drifts and mismatches are no longer a problem. LED1 acts both as a rail-splitter and a power indicator, while LED2 gives a simple low-battery warning. T

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Other Materials from the Main Document

• Article «Newer, shinier DMM RTDs. Part 2»
• Figure 1. Using a precision op-amp lets us set the output reference level with a passive network because thermal drifts and mismatches are no longer a problem. LED1 acts both as a rail-splitter and a power indicator, while LED2 gives a simple low-battery warning. T
• Figure 2. Adding a biasing network to A1 allows its output to be at 0 mV (common) when sensing 0 °C, and to swing negative for lower temperatures
• Figure 3. Plotting the errors for various values of R5 - the positive feedback resistor - shows that we can optimize performance for minimal errors around 0-100 °C (magenta) or accept a wider error band over a greater temperature range. The red curve is within
• Figure 4. Changing three components gives an output of 1 mV/°Fahrenheit
• Figure 5. A small negative offset allows the basic circuit to give an output directly proportional to absolute temperature
• Figure 6. Stripping out all the frills and fancies leaves a basic circuit that is ideal for running off split rails and compatible with most ADCs
• Figure 7. Referring the output from the amplifying stage to either a positive reference or to common allows the indication to be switched between Celsius and Kelvin