Nixie Thermometer

[threeneurons]

Here's a little nixie project. Its a thermometer, it has a 2-1/2 digit display, with a simple NE-2 in the 1xx position. I decide to build a decrete dual slope ADC circuit, to convert the temp voltage from a LM34 to a digital readout. Since a dual slope converter has a rising and falling ramp (with a steady DC input), it just begged to have a IN-13 bargraph following that signal.

Here a video:

http://www.dailymotion.com/video/x2i8c95_nixie-thermometer_tech

And more details:

https://threeneurons.wordpress.com/nixie-power-supply/nixie-thermometer/

Enjoy !

[Joe Croft]

Nice job! I like it.

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[AlexTsekenis]

Very intriguing way of going about creating/tapping into a ramp signal to drive the bargraph. Nice!

Alex

[gregebert]

Are the IN-13's behaving linearly, or at least are they monotonic and repeatable ?

I experimented with some IN-9's and found them to be very erratic. I'm about ready to throw them out.

[AlexTsekenis]

For the IN-13, if the cathode is not poisoned, they are linear within some tolerance of course. They become increasingly non-linear near full coverage of the cathode; about 1-2 cm from the top. Treating them as linear within two regions each with each own slope has been a great approximation.

Cant comment on IN9s

Alex   

[threeneurons]

I had to think a little about that one. The easiest way to drive them, is using an NPN, with an emitter resistor, and sending the input to the base. Then the emitter will follow the base. The emitter current will follow that signal, as a function of voltage across the emitter resistor. The collector is roughly the same as the emitter current, less the base current, which can almost be ignored. 

The ramp, on this circuit, is always negative, relative to the analog portion's common (AREF). Maximum signal, is most negative, relative to AREF. The bar length is roughly proportional to the current flowing thru them. So instead of driving the base, I tied that one to near AREF, and fed the signal to the emitter. But the emitter has a lower impedance, and needs more drive current. That's why I added the PNP, as an emitter follower. The signal is fed into the base of that PNP. Its emitter follows the input. The base of the HV NPN, is fixed at roughly two diode drops (~1.2V) higher than AREF. The voltage drop, then, across the 1K resistor between these two transistors, roughly equals the ramp voltage. The current then thru both, and thru the bargraph is roughly that voltage divided by 1K. I designed the integrator to peak at -5V (relative to AREF), with 1.5V in (or 150 F) from the LM34. That translates to 5mA, which will "peg", the IN-13.

I like the IN-13 over the IN-9, mostly because it uses less current. The aux cathode helps keep the bar at one end. Its no guarantee, however. A friend of mine has a simple IN-13 winker, which now has its glow floating around the tube. These are odd tubes, which are designed to partially glow. It jut looks like a recipe for cathode poisoning. 

[AlexTsekenis]

Tell your friend to add a strong small magnet on the tube, if the glow is not anchored, the glow will stick to the magnet and you can move it around.

[GastonP]

Beautiful!
If you had made it for the real world (which measures temperature in degrees Celsius), you wouldn't need the NE-2

:D

Gastón

[threeneurons]

If I use a LM35 instead of an LM34 then it will automatically be in C.

What needs to be added then is an absolute value stage (precision rectifier circuit), with a sign indicator, for negative values. Both the LM34 and LM35 should be able to be rigged for negative values.

[Alex]

Nice, I particularly like the use of the 0.01uF cap to allow the resetting of the decade counters by their enable line for commencing a new 64 HZ count...

[John Rehwinkel]

> Here's a little nixie project. Its a thermometer, it has a 2-1/2 digit display, with a simple NE-2 in the 1xx position. I decide to build a decrete dual slope ADC circuit, to convert the temp voltage from a LM34 to a digital readout. Since a dual slope converter has a rising and falling ramp (with a steady DC input), it just begged to have a IN-13 bargraph following that signal.

Oh, that's just neat to watch. I'm also building slope generators, but they're for vector generators for some CRT art projects.

- John

[threeneurons]

It was common practice, with 4000 CMOS. What Don Lancaster called MM Logic. MM for "Mickey Mouse". I sure hope Disney doesn't sue this forum now !