Author Topic: steve30's Digital thermometer project  (Read 8535 times)

steve30

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steve30's Digital thermometer project
« on: August 12, 2012, 10:25:47 AM »
I was looking through a few of the interesting projects in this section, so I thought I'd post an intro to the digital thermometer project I've started, in case it is of interest to anyone.

Its not too complex. Its an ICL7107 digital voltmeter IC and its going to have a temperature sensor and associated circuits connected to its input.

Currently I just have the 7107 and the display built up on a matrix board. Something quite remarkable about the matrix board version, is that it worked first time :). That rarely happens 8).






Hopefully it will have several input channels, and be able to display either Celcius or Farenheit. I think I'll start by using an LM335 temperature sensor as I have some experience with these from a few years ago.

This could probably be accomplished by using a programmable device, but I've never used microcontrollers and I find it cool to see stuff these days that isn't programmable.

Any ideas welcome.
« Last Edit: August 12, 2012, 10:27:52 AM by steve30 »

Kiriakos GR

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Re: steve30's Digital thermometer project
« Reply #1 on: August 12, 2012, 12:06:36 PM »
Wow... a true Intersil IC plus other true components.  :)

It is time to get a true high quality case for it.

steve30

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Re: steve30's Digital thermometer project
« Reply #2 on: August 12, 2012, 12:38:22 PM »
Once I've got all the temperature measurement circuits working, I'll probably get it made on a nice PCB, and then pick a case for it. :)

MJLorton

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Re: steve30's Digital thermometer project
« Reply #3 on: August 13, 2012, 04:48:48 AM »
Once I've got all the temperature measurement circuits working, I'll probably get it made on a nice PCB, and then pick a case for it. :)
Brilliant, thanks for posting it Steve.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

steve30

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Re: steve30's Digital thermometer project
« Reply #4 on: August 16, 2012, 02:20:09 PM »
I just thought I would point out the seven segment displays in case it is of interest to anyone.

These are pretty cheap 'OptoSupply' brand ones, which I got from Rapid Electronics: http://www.rapidonline.com/Electronic-Components/14-2mm-Pure-Green-Seven-Segment-Display-Cathode-200mcd-57-0131/?sid=1f193141-2f4c-410d-a1d6-9a5fdced5f7a

This is the pure green one, which has a luminous intensity of 200mcd at its maximum forward current of 20mA. That is very bright. Probably too bright. But, these are readable with only a few microamps, and a reasonable brightness can be obtained with less than 1mA.

This actually makes them very good for this temperature monitor since it is going to run off batteries. At the moment, the whole thing only takes around 10mA.

I recently bought some tiny seven segments for my multimeter retrofit (http://www.eevblog.com/forum/projects-designs-and-technical-stuff/multimeter-display-mod-project/) and they really need 10mA per segment for their full brightness and even then aren't that bright. I need to get some brighter small ones.

Just an interesting little comparison.
« Last Edit: August 16, 2012, 02:25:02 PM by steve30 »

steve30

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Re: steve30's Digital thermometer project
« Reply #5 on: August 21, 2012, 12:26:47 AM »
I've done a bit of playing around, and now it measures temperature!

I added a power supply board, which provides a stable +5V from a Microchip MCP1700 regulator. The 7660 chip then provides a -5V. The other board interfaces the LM335Z sensor to the voltmeter by removing its Kelvin offset, thus giving a reading in Celcius.

Seems to work reasonably well :).

Here's a couple of pictures of it working. On this occasion it wasn't quite agreeing with the mercury thermometer, but close enough. Unfortunately, my camera struggles to pick up the nice green colour of the LEDs.






Just needs a decimal point now ;).