EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: jismal on March 12, 2018, 05:29:13 am
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Hello all
Could anyone find out a Thermistor ic which could operate at low voltage as 2.5v and high as 5v.
I could only find some couple of them. The project is to make a device which is battery powered (3V-2.7V)which can sense temperature using thermostat. I cannot use a boost converter for this as it made to be a low cost solution. The collected data is pushed via BLE 4.0 to an android app.
1) MAX6682.(3v to 5v)
2) LTC2983(2.85 to 5.25v) :-//
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...which can sense temperature using thermostat...
Err, I think 'thermostat' isn't the word you're looking for. Those tend to be on/off devices.
If you want to use a thermistor, you can do that in a few ways. A cheap but effective method is to make a resistive divider and use a micro controller ADC, then correct for non-linearity with some calibration curve. The power to the divider can be switched on and off with an IO pin and a P channel MOSFET to reduce sleeping current consumption.
It depends a lot on your accuracy, noise, and protection requirements. Do you want the thermistor on the PCB, or mounted off the PCB on some wires? What temperature range and accuracy do you want?
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No i am looking for thermistor based solution so i could place the sensor in the skin and acquire the data. I am looking for a single chip solution because i maxed out the adc channel in the controller i am using. I also cannot use any other solution which requires a calibration of some sort. Desperately looking for a single chip solution. Anyway accuracy will be of +-2 degree Celsius.
Thank u you for your fast reply jbb :-+.
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OK, you’ll have to do some error calculations, I don’t know if you can do 2 deg C accuracy without calibration.
Have you considered a dual analog MUX chip? Use 1x GPIO for control. Use 1 MUX to switch between normal analog input and thermistor network. Use second MUX to energise thermistor network.
To minimise drift, the measurement should be ratiometric. That is, the power supply to the thermistor chain should be the same as the reference voltage. This removed changes in reference voltage from your error sources.
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DS18B20 - minimum = 3 V.
DHT12 - 2.7 V.
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I have used the LTC2983 at work, and it works very well. Accurate to +/- 0.1*C with a $10 thermistor. It has something like 20 channels available for different temperature measuring devices (diodes, thermocouples, RTDs), but I think LT has made one a little cheaper with 10 channels (LTC2985 maybe?). Only downside is that it maxes out at 6 samples per second per channel. Also not particularly cheap in single quantities ($30)