Timeline for How can I use a 2N2222 transistor as a temperature sensor?
Current License: CC BY-SA 4.0
68 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 12, 2020 at 3:56 | history | edited | tlfong01 | CC BY-SA 4.0 |
edited body
|
| Oct 12, 2020 at 3:32 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 209 characters in body
|
| Oct 8, 2020 at 17:04 | comment | added | D.A.S. | Let’s not discuss and simply say what range and accuracy specs 1st? Room temp or outdoor 0~70’Cor whatever? 2’C is easy , 0.5’C must reduce range. Need accurate gain like R ratios in Amp 0.5% an very low diode current with cap. Then 2.1’mV/‘C +/-0.1 with pot cal. Using ice and boiling water | |
| Oct 8, 2020 at 15:19 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 397 characters in body
|
| Oct 8, 2020 at 15:03 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 764 characters in body
|
| Oct 8, 2020 at 14:33 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 205 characters in body
|
| Oct 8, 2020 at 8:34 | comment | added | tlfong01 | Let us continue this discussion in chat. | |
| Oct 8, 2020 at 6:16 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 156 characters in body
|
| Oct 8, 2020 at 6:10 | comment | added | tlfong01 | Ha, so I need to get a volt meter in 10 μA range? You remind me that ages ago, when I was educated in college to become an engineer. I was told that any engineer worth his salt must always remember 6 words by heart: (1) Reliability, (2) Tolerance, (3) Accuracy, (4) Trade off, (5) Benefit, (6) Cost. Ah, I am missing my locking down lunch. Nice chatting with you. See you later. | |
| Oct 8, 2020 at 5:50 | comment | added | D.A.S. | actually the tempco increases from -2.0 to -2.2 as the current is reduced to 1uA. Any self heating is undesirable too with small plastic parts @ 0.2'C/mW | |
| Oct 8, 2020 at 5:16 | comment | added | tlfong01 | Ha, yes, the 2.2mV/C° elites are laughing loudly at the YTs, which of course are newbies' sorrows. | |
| Oct 8, 2020 at 5:13 | comment | added | D.A.S. | I don't consider any of those YT's video's as expert design references | |
| Oct 8, 2020 at 5:08 | comment | added | tlfong01 | @Tony Stewart Sunnyskyguy EE75, If you watch the videos in my reference list #20, 21, which I suppose are the "best" YTs on this subject, because Google ranks them at the very top. I do think that the alien EE engineers in our neighour galaxy are now LOLing at our high school students weeping in the dark. | |
| Oct 8, 2020 at 4:54 | comment | added | tlfong01 | @Tony Stewart Sunnyskyguy EE75, Ah yes, everybody is talking about the magic number Vbe 2.2mV/C°. However, I am just a high school student, and my cheapy multi-meters have a ridiculously tiny current range of 2mA.And the real scientists are talking about the μAs. So the whole world's high school students are weep in the dark.:( | |
| Oct 8, 2020 at 4:53 | comment | added | D.A.S. | but great effort | |
| Oct 8, 2020 at 4:23 | comment | added | D.A.S. | When you combine a fairly accurate - 2.2mV/'C NTC characteristics of the Vbe with base-collector shorted and then use a common emitter with hFE changing with T you get an inaccurate temperature sensor. -1 | |
| Oct 8, 2020 at 3:45 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 367 characters in body
|
| Oct 8, 2020 at 3:13 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 207 characters in body
|
| Oct 8, 2020 at 1:22 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 316 characters in body
|
| Oct 7, 2020 at 7:53 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 268 characters in body
|
| Oct 7, 2020 at 5:32 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 168 characters in body
|
| Oct 7, 2020 at 5:10 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 199 characters in body
|
| Oct 7, 2020 at 4:38 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 265 characters in body
|
| Oct 7, 2020 at 4:16 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 73 characters in body
|
| Oct 7, 2020 at 3:55 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 197 characters in body
|
| Oct 6, 2020 at 14:44 | comment | added | tlfong01 | As you said, grasping concept, doing/learning/appreciating engineering design, trade off, cost benefit analysis, and the joy of DIY/making things or just a toy, even the project ends up a "failure", is important, not accuracy or applicability | |
| Oct 6, 2020 at 14:38 | comment | added | tlfong01 | But in many applications, eg, measuring the temperature of warm water in a bath, or even room temperature to control air conditioner/heater, an accuracy of two degrees is acceptable. My objective in making this answer is educational, learning how to read a datasheet, idea of non linearity and how to use software to workaround. Accuracy is never a requirement in my suggested DIY sensor, because it is not supposed as a accurate scientific instrument. / to continue, ... | |
| Oct 6, 2020 at 14:31 | comment | added | tlfong01 | @Transistor, Ah yes, I am not surprised to discover that the OP is just a 15 year old student and a member of a computer hobbyist club in his school. My thinking is that he might be happy if we guide him to read the datasheets and how he can convert the 2N2222 into a temperature sensor, however crude or non linear his converter sensor it is. I guess even the designer of TMP36 is doing some sort of curve fitting/straighten to make final product linear and accurate. We might explain to the OP, that even if we cannot DIY a temperature sensor with accuracy of 0.5 degree. / to continue, ... | |
| Oct 6, 2020 at 14:21 | comment | added | tlfong01 | @Sredni Vashtar, I agree with you that the vendor packages 2N2222 with pinouts as ordered by the Japanese buyers. I also notice that the new datasheets provide different styles of pin layouts for customers to order. | |
| Oct 6, 2020 at 14:19 | comment | added | Transistor | Also note that the OP thought that the TMP36 was comparable to a 2N2222 so most of this is probably way over his/her head. Pitch the answers so that the OP has to reach just a little to grasp the concepts. | |
| Oct 6, 2020 at 14:15 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 1388 characters in body
|
| Oct 6, 2020 at 7:37 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 86 characters in body
|
| Oct 6, 2020 at 6:58 | history | edited | tlfong01 | CC BY-SA 4.0 |
deleted 1124 characters in body
|
| Oct 6, 2020 at 6:43 | history | edited | tlfong01 | CC BY-SA 4.0 |
deleted 1124 characters in body
|
| Oct 6, 2020 at 6:23 | history | edited | tlfong01 | CC BY-SA 4.0 |
deleted 6416 characters in body
|
| Oct 6, 2020 at 6:00 | comment | added | tlfong01 | @Voltage Spike, Thank you for your advice. Actually some of the suggestions and tests in my answer are out of date, misleading and plain wrong. So I have decided to set up a GitHub page, and place the datasheet summaries there. This way I can make my answer perhpas many times shorter, and only refer to my GitHub page for not too relevant details. Thanks again. Cheers. | |
| Oct 6, 2020 at 5:39 | comment | added | Voltage Spike♦ | @tlfong01 Please keep your edits to a minimum and your answers a bit shorter, the answers are a bit long. Thanks | |
| Oct 6, 2020 at 5:24 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 214 characters in body
|
| Oct 6, 2020 at 4:45 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 205 characters in body
|
| Oct 6, 2020 at 4:17 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 554 characters in body
|
| Oct 6, 2020 at 3:45 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 406 characters in body
|
| Oct 5, 2020 at 16:59 | comment | added | Sredni Vashtar | tlfong, my opinion is that the pn2n2222 was created for the Japanese market (I have no hard evidence, though) where transistors have usually the CBE pinout, opposite to the customary (but not universally shared) EBC pinout of American and European transistors (I am talking about small signal BJTs - power transistor are another thing and the usually have to middle pin connected to the collector or drain). | |
| Oct 5, 2020 at 15:08 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 2424 characters in body
|
| Oct 5, 2020 at 14:55 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 2424 characters in body
|
| Oct 5, 2020 at 9:07 | comment | added | tlfong01 | @glen_geek, now I have set up the test circuit to test out your suggestion of using 1MR for Rb, varying Rc and see how it goes. I have also update the circuit and put it at the very top of my answer. Comments and counter suggestions welcome. Cheers. | |
| Oct 5, 2020 at 9:03 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 106 characters in body
|
| Oct 5, 2020 at 2:49 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 1609 characters in body
|
| Oct 4, 2020 at 14:59 | comment | added | tlfong01 | I now see our approach is odd, because it is not like the photo transistor, which sort of using CE junction, without electrical but only photo/light input from base. Of course I know I can just use a diode, which according to the (Schottky?) diode equation, is current dependent to temperature. Anyway, I will stop selfie brainstorming, and start experimenting @glen-geek's geek tip.. | |
| Oct 4, 2020 at 14:53 | comment | added | tlfong01 | @glen_geek. Ha, many thanks for your instruction, which I think is simple and concise. I must confess I don't know at all your rationale or theory behind. But it so simple, so I guess both me and the OP which I guess is around 16 old student can also blindly follow your tip, and then do some measurement to see if your circuit might lead to anything promising. Then I will study the datasheet or other theories behind, and try to find why you suggest your design. / to continue, ... | |
| Oct 4, 2020 at 13:12 | comment | added | glen_geek | That 2N2222 circuit shown here with one base resistor, and one collector resistor is about the best you can do for a simple temp sensor. However, choice of resistor values depends greatly on transistor \$Hfe\$, which varies greatly from device-to-device. Try a base resistor of 1Meg, and then choose Rc so that collector voltage is roughly half-way at room temperature. | |
| Oct 4, 2020 at 9:12 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 270 characters in body
|
| Oct 4, 2020 at 9:02 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 299 characters in body
|
| Oct 4, 2020 at 8:36 | comment | added | tlfong01 | @Sredni Vashtar, Many thanks for your very important and critical warning. Do you know why some chips have the two terminals inverted? In my long electronics hobbyist life, I have never heard of such a ridiculously dangerous pinout trap, for newbies, ninjas, and even pros alike. | |
| Oct 4, 2020 at 8:31 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 141 characters in body
|
| Oct 4, 2020 at 7:51 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 125 characters in body
|
| Oct 4, 2020 at 7:11 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 102 characters in body
|
| Oct 4, 2020 at 7:06 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 102 characters in body
|
| Oct 4, 2020 at 6:43 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 2 characters in body
|
| Oct 4, 2020 at 5:27 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 147 characters in body
|
| Oct 4, 2020 at 4:57 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 133 characters in body
|
| Oct 4, 2020 at 4:52 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 133 characters in body
|
| Oct 4, 2020 at 4:34 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 109 characters in body
|
| Oct 4, 2020 at 4:13 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 270 characters in body
|
| Oct 4, 2020 at 4:05 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 270 characters in body
|
| Oct 4, 2020 at 3:49 | comment | added | Sredni Vashtar | The dreadful P2N2222 is about to strike again. To the OP: watch out for inverted C and E terminals, if you have a 2N2222. | |
| Oct 4, 2020 at 3:45 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 315 characters in body
|
| Oct 4, 2020 at 3:37 | history | edited | tlfong01 | CC BY-SA 4.0 |
added 516 characters in body
|
| Oct 4, 2020 at 3:28 | history | answered | tlfong01 | CC BY-SA 4.0 |