Hi all. I am designing a PIC or AVR with temperature sensor.
Two I have found are the Linear Active Thermistor LM35 and Microchip mcp9700. Unfortunately, they do not have the resolution I need:
Range 33c-40c (less than 7degC range)
Accuracy better than .01C
Response seconds
Distance skin contact, or intimate to skin

Both chips above only do 10mv/1c. Sure they can be boosted by another analog device, but specs demand minimal parts.
The 8-bit PIC comparator is likely not as suitable as the 10-bit AVR device.

I have never designed temperature sensors, and all designs seem to cater for wider temperature ranges.
Which leads me to the main question - given the above parameters, is there an IR receiver that does not need a sender, with better resolution than aforementioned?
There is a ic manufacturer Vishay, which seems to be one of the market leaders, but I really need to ascertain if IR is better than the previous mentioned packages?

Hope I've provided sufficient information here. There are 2 other threads on this forum, but do not address the needs mentioned here.
Any suggestions gratefully received.
Kind regards,
Alistair

 

You may get the resolution you need with a different A to D converter (not comparator). The hard part is the level of voltage you are working with. You can try to resolve fractions of millivolts with something like a 22 bit audio A to D, or you can offset and amplify the LM35 outout to the 7 degC span runs from 0 to 5 volts. That scales to 714 mv/degC, or 7.14 mv/.01 degC. A 10 bit A to D can just resolve that (4.9 mv/bit).

The accuracy figure is going to be expensive and require additional hardware.

 

Hi thanks for info. From what Ive been able to ascertain Thermistors provide the best accuracy. Some items here may be suitable.
http://www.amwei.com/news.asp?news_id=79
These devices are providing a 1k2 swing in the 35-40degC range/240Ω/deg/>1% accuracy.

However, I am still most interested in Infrared, as the desired temperature is underneath the skin.
Any contributors on infrared?
Al.

 

Thermistors are a reasonable choice for a limited range. They are no too linear, but the deviation in 7 degrees should be negligible. There will be a published curve to insure negligibility.

No opinion on IR.

 

Thermistors are a reasonable choice for a limited range. They are no too linear, but the deviation in 7 degrees should be negligible. There will be a published curve to insure negligibility.

No opinion on IR.

Thank you. There is very little info on i/r. Obviously it must be somewhere - take for example the in-ear thermometers I guess they would use i/r. They must be pretty accurate too.
Kind regards,
Alistair.

 

True, I looked at that. It certainly seems the best option, however Digikey is expensive. I did contact the maker of the product but they havent replied I guess my few thousand quantity is not sufficient for them. It must be cheap.
Al.

 

I think you're going to have the best results with a thermocouple wire.