Re: "Nixietherm" IN-9 bargraph based thermomer

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3 months 5 days ago #11624 by Ty_Eeberfest
1) Different Schematics
I would use the one from Instructables since it has the most recent date on it (in the title block)

2) Transistors T3 and T4
Obviously T3's symbol is wrong - the circuit would never work like that! That "BeerLogic" discussion is nothing but beer logic i.e. confusion. If you look up the data sheet for BC639 you will see it is an NPN transistor which is correct. Also, T1 is an MJE 340 not MJE34xx. You could use a MPSA42A instead if you want to.

3) Value of L1
It's not a conventional inductor and doesn't really have a value (the schematic symbol told me this). It is a common mode suppression choke and you don't really even need it.He probably put it there to serve as a "second environment filter" to try to comply with some EU regulation that can be ignored because you are building it for personal use not for sale.

4) Temperature Range
You really should read Page 4 of the manual I linked you to in my last post, the section called "Adjusting of the Measurement Amplifier". Also read the paragraph in the Instructible that starts with "Now have a short look to the temperature measuring ciruity.". Also look at the data sheet for the LM35 sensor.

From looking at all those resources I can see that the LM35 sensor is no good below 0*C. So you need a different sensor, either an industrial style RTD or a thermistor with sufficient range and linear response characteristics. The temperature amplifier circuitry is nothing but a linear amplification stage followed by a subtraction stage. When you feed 350mV into it the Nixie goes to full scale. When you feed it 100mV the Nixie goes to minimum on the scale. To say it more correctly, it is a linear display with a span of 250mV (yes 250 which is 350 - 100) and zero offset of +100mV.

So... your sensor needs to produce 100mV at -20*C and 350mV at +40*C. This is easily done using a thermistor and one or two fixed resistors forming a divider. Also note that the span and zero offset of the circuit can be adjusted somewhat using the pots TR1 and TR2.

If you have further questions I'll try to answer them. But remember: this is not my design, this is not my product, I never really looked at it until recently, I've never built one, and I don't usually design people's projects for them.

Look into it later when the dust is clearing off the crater.

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3 months 5 days ago #11625 by Jean
Thanks for your answer, it was very helpful.
I almost thought it was a drawing error with the transistors.
If you could tell me which inductor (L1) to use, then ok, otherwise it will stay out.
I can only see pictures and chats on page 4 of your link, but not what you described in your message.
Could you make me a non-binding suggestion for the sensor / thermistor and possibly a small drawing of the circuit with the resistors?
Since I am not a full-time electronics technician, only one year of school experience, I am not so skilled with sensors or thermistors. But my level as a layperson is very high. My last project (replica) was a Nixie watch with IN13 and personal change, such as EU / US Adaptation (see attachment).
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3 months 4 days ago #11626 by Ty_Eeberfest
Go to this post:
www.tubeclockdb.com/forum/4-builders-for...rmomer?start=30#1773
and download the PDF that is attached to that post. It is the construction manual for the original NixieTherm. The schematic isn't up to data but the part discussing principle of operation, calibration, etc, is still useful.

I am finding I spoke too soon about the thermistor. It's harder than I thought to find one that is linear. I'll look at other options tonight and let you know what I find out. Is it really necessary to be able to go below 0*C?

As for the common mode choke there are literally thousands to choose from that would work okay. Look at the attached PDF for one possible type. SSR10H-04910 would be a good choice.

This browser does not support PDFs. Please download the PDF to view it: Download PDF


Look into it later when the dust is clearing off the crater.
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3 months 4 days ago #11629 by Jean
I've already read these discussions. These only become interesting when the circuit is set up on the test board, then comes the fine work.
Thanks for the type of inductor, will take him.
It is not necessary to go below 0ºC, min. + 2ºC is enough for me, so the LM35 is enough. Is for indoor, but would not be bad as an option. If you can't find anything, it's not a problem.

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3 months 4 days ago #11630 by Ty_Eeberfest
Okay... I have thought about this and done some maths. Here is what I came up with. Remember - I am not an analog wizard and I haven't actually tested any of this. On paper it seems okay.

This is all based on the schematic from Instructables, This should give you a range of -20*C to +40*C.

1) My thermistor idea is no good. Instead I decided that the LM35 should be replaced with an LM61, This one:
www.mouser.com/ProductDetail/Texas-Instr...psfTFMsEvglySA%3D%3D

2) The gain of IC2A needs to be changed from 18 to 7.5. (this is the "slope" or ""span") To do this, remove R3 completely and change R4 to 2K. Adjust TR1 so that the voltage at test point UTemp = 7.5 times the voltage at test point ULM35.

3) This leaves a 3 volt offset that has to be gotten rid of by IC2B. To do this, change R15 to 620 ohms. Adjust TR2 so that the voltage at test point URef is about 4 volts. (this is the "offset" or "intercept") Later you can fine-adjust TR2 to get the display just right.

Did you notice that the Instructables design uses an IN-13 tube (Jurgan's original uses IN-9) ? They are similar but not identical which would explain some of the changes we see in the Instructables schematic.

Look into it later when the dust is clearing off the crater.

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3 months 4 days ago - 3 months 4 days ago #11631 by Ty_Eeberfest
I just saw your last post. We were typing at the same time.

If you go with the LM35 then you can probably use the resistors that are shown on the schematic, i.e just build it as it is shown. Then adjust TR1 for a gain of 19 or so to stretch the range out to 2*C - 40*C.

Regarding the common mode choke, the one I selected has a nice peak at about 100KHz which will be good for keeping the switching noise of the 125V boost converter from "escaping". I believe this was Jurgen's intention.

Look into it later when the dust is clearing off the crater.
Last edit: 3 months 4 days ago by Ty_Eeberfest. Reason: Typo

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