Timeline for How can I use a 2N2222 transistor as a temperature sensor?
Current License: CC BY-SA 4.0
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| Oct 5, 2020 at 16:06 | history | edited | Spehro 'speff' Pefhany | CC BY-SA 4.0 |
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| Oct 5, 2020 at 8:24 | comment | added | Spehro 'speff' Pefhany | At 1.1V a single diode-connected transistor with a 10K series resistor to +5 would work very nicely. Resolution about 0.5°C. Might have to average a bunch of readings. | |
| Oct 5, 2020 at 8:13 | comment | added | Edgar Bonet | Note that on most Arduinos you can set the voltage reference of the ADC to some internal reference lower than Vcc: 1.1V or 2.56V on AVR boards, 1.0V on the SAMD boards... | |
| Oct 5, 2020 at 7:04 | comment | added | user57037 | Well, I would just try it. With a cap at the BE junction the AC impedance will be very low. Leakage or resistance looking into the ADC will calibrate out to some extent. | |
| Oct 4, 2020 at 15:40 | comment | added | Spehro 'speff' Pefhany | @Ferrybig There are techniques for allowing several hundred K input impedance without significant error (10n cap + certain delays), or reduce the resistors 5:1 for similar results. | |
| Oct 4, 2020 at 15:31 | comment | added | Ferrybig | Note that you need an OP amp in order to read the signal using an Arduino (as the OP mentions in the main question). The Arduino required an impedance of 10kOhm or lower in order to stay within spec for the analog inputs | |
| Oct 4, 2020 at 11:38 | history | edited | Spehro 'speff' Pefhany | CC BY-SA 4.0 |
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| Oct 4, 2020 at 4:59 | comment | added | user57037 | The sensitivity depends inversely on bias current. Lower bias current will give slightly higher sensitivity. And I am not sure but I think maybe a couple hundred microamps will give sensitivity of more like 1.8mV per degree. I think maybe 10uA is enough, but I guess it depends on the ADC leakage current spec. You want the bias current to be much higher than the ADC leakage current. | |
| Oct 4, 2020 at 2:47 | history | answered | Spehro 'speff' Pefhany | CC BY-SA 4.0 |