A Day Late and a Volt Short

I'm not happy with myself. I overlooked something fundamental regarding the temperature sensor project. It was to work in the Fahrenheit scale and in accordance with the demands of small size and low power everything was to work off of one 3V type CR2032 lithium battery.

I've worked with the LM35 Precision Centigrade Temperature Sensor before. It's a good sensor but won't work in this project because it's approximate 1^oC accuracy is too course. Also without a negative power supply it bottoms out at 2^oC. That is low enough for here in Northern California, where it rarely freezes. Elsewhere lower temperature are far more common and the point of the sensor is to detect and record highs and lows.

I've ordered a couple of LM34s, these are Fahrenheit sensors, so I get the resolution I want. Without a negative power supply these bottom out at 4^oF, that's much better. This is plenty cold to be useful everywhere but the coldest laboratory freezers, polar weather stations or Minnesota.

Just one small, 2 volt problem. The LM34 and LM35 both require a 5V power supply, not 3V. I guess I get to start again...

I've begun a search for a precision temperature sensor that works at 3V. So far they have all been Centigrade only. Often with a ±3^oC accuracy. I don't see how these can be labeled "Precision". I can work with a Centigrade sensor if it has a ±¹/₂^oC accuracy.

So far the other sensors that work at 3V have been more complex affairs with built in ADC and I²C interfaces, etc. These might work. If so then I could drop the requirement that the PIC have a built in ADC.

I'm still searching...