I wanted to familiarize myself with Microchip’s MCP9700 thermistor ICs for some upcoming projects that require temperature measurement / compensation.

I decided to build a simple circuit around the MCP9700 to convert an old analog micro-ammeter into a thermometer for the lab. It displays 1uA per degree Celsius, has an output of 1mV per degree Celsius for external temperature monitoring / data logging, and draws only 20uA from a 5V supply.

Not only is it a cool looking centerpiece (I’ve always found old analog meters absolutely beautiful), it’s quite useful too!

The circuit is very simple: the LCT1541 op-amp is configured as a differential amplifier, converting the output voltage from the MCP9700 into 1mV per degree Celsius. This is used to drive the micro-ammeter to display 1uA per degree Celsius.

Except for R2 and R7, all resistors used were precision .1% types; U2b is the band-gap voltage reference integrated into the LTC1541. A more thorough circuit description and demonstration is available in the video:

While this initial design works, there are definite shortcomings. Stay tuned for updates on design critiques and improvements!

References:

MCP9700 datasheet (microchip.com)

LTC1541 datasheet (linear.com)

AA battery discharge tests (powerstream.com)