Ambient temperature sensing

[Jason S]

Hi,

I'm looking for a circuit that will represent temperature ranges up to 60
degrees (celcius) using at least 3 LED's or transistors as the outputs for
each range, but I DO NOT want a digital display like a 7-segment or LCD
though.
I want to be able to utilize these outputs to control others parts of my
circuitry (perhaps like voltage calibration).

Example:
LED 1 (green) = -10-20 degrees,
LED 2 (yellow) = 20-30 degrees,
LED 3 (red) = 40+ degrees,

I am open to all suggestions.
Thanks in advance.

J

 

[Asimov]

"Jason S" bravely wrote to "All" (01 Dec 05 21:12:24)
--- on the heady topic of "Ambient temperature sensing"

JS> From: "Jason S" <[email protected]>
JS> Xref: core-easynews
JS> sci.electronics.repair:350096


JS> Hi,

JS> I'm looking for a circuit that will represent temperature ranges up to
JS> 60 degrees (celcius) using at least 3 LED's or transistors as the
JS> outputs for each range, but I DO NOT want a digital display like a
JS> 7-segment or LCD though.
JS> I want to be able to utilize these outputs to control others parts of
JS> my circuitry (perhaps like voltage calibration).

JS> Example:
JS> LED 1 (green) = -10-20 degrees,
JS> LED 2 (yellow) = 20-30 degrees,
JS> LED 3 (red) = 40+ degrees,

JS> I am open to all suggestions.
JS> Thanks in advance.


J,

You might try crossposting to sci.electronics.design.

Your circuit needs a voltage reference and a window comparator.
The voltage reference is used with a temperature probe and the window
comparator will divide your output into 3 ranges. With some cmos
gating you can readily light 3 separate leds.

A*s*i*m*o*v

.... I worked hard to attach the electrodes to it.

 

[Tony Marsillo]

Jason,
You could try the LM34 and LM35 series of temperature sensors from National
Semi. There output is linear with temp. 10mv/degrees F for the LM34. The
LM35 is 10mv/degrees C. The output can then drive a few comparators with the
appropriate trip points.

http://www.national.com/ds/LM/LM34.pdf

http://www.national.com/ds/LM/LM35.pdf

 

[James Sweet]

Hi,

I'm looking for a circuit that will represent temperature ranges up to 60
degrees (celcius) using at least 3 LED's or transistors as the outputs for
each range, but I DO NOT want a digital display like a 7-segment or LCD
though.
I want to be able to utilize these outputs to control others parts of my
circuitry (perhaps like voltage calibration).

Example:
LED 1 (green) = -10-20 degrees,
LED 2 (yellow) = 20-30 degrees,
LED 3 (red) = 40+ degrees,

I am open to all suggestions.
Thanks in advance.

J

How about an analog bargraph IC? Otherwise a quad comparator chip could
be setup to do this, IIRC the LM329 is such a chip.

 

[Jason S]

How about an analog bargraph IC? Otherwise a quad comparator chip could be
setup to do this, IIRC the LM329 is such a chip.

Hi thanks for the reply.
The quad comparator wouldn't really work, because only 1 'output'
LED/Transistor needs to be lit at any given time, not more than 1. The
analog bargraph would probably work, but would need to be able to set it up
as 'Dot' mode (probably easy to do), then I could use logic gates to provide
filtering from each of the outputs to produce my final 3 or 4 output ranges.
However, any ideas on how to hook up a temperature sensor to it? I found
schematics based on voltage measurement, not I know nothing about temp
sensors and how I would hook it up with this type of circuit. Can you point
me in the right direction?

Thanks, J

 

[Sjouke Burry]

Hi thanks for the reply.
The quad comparator wouldn't really work, because only 1 'output'
LED/Transistor needs to be lit at any given time, not more than 1. The
analog bargraph would probably work, but would need to be able to set it up
as 'Dot' mode (probably easy to do), then I could use logic gates to provide
filtering from each of the outputs to produce my final 3 or 4 output ranges.
However, any ideas on how to hook up a temperature sensor to it? I found
schematics based on voltage measurement, not I know nothing about temp
sensors and how I would hook it up with this type of circuit. Can you point
me in the right direction?

Thanks, J

Use a darlington transistor, for silicon the leak current doubles
every 6 degrees celcius,and the leak current of the first
transistor multiplied twice by your current gain should be
around the Milliamp range.Up to about 100 degrees,works nicely.
Add 3 comparators to check for voltage level across a suitable
resistor,you could use a quad IC 741 type for that.

 

[James Sweet]

Hi thanks for the reply.
The quad comparator wouldn't really work, because only 1 'output'
LED/Transistor needs to be lit at any given time, not more than 1. The
analog bargraph would probably work, but would need to be able to set it up
as 'Dot' mode (probably easy to do), then I could use logic gates to provide
filtering from each of the outputs to produce my final 3 or 4 output ranges.
However, any ideas on how to hook up a temperature sensor to it? I found
schematics based on voltage measurement, not I know nothing about temp
sensors and how I would hook it up with this type of circuit. Can you point
me in the right direction?

Thanks, J

A quad comparator has four outputs, there's four comparators, seems like
it would do exactly what you need.

 

[Franc Zabkar]

Jason,
You could try the LM34 and LM35 series of temperature sensors from National
Semi. There output is linear with temp. 10mv/degrees F for the LM34. The
LM35 is 10mv/degrees C. The output can then drive a few comparators with the
appropriate trip points.

http://www.national.com/ds/LM/LM34.pdf

http://www.national.com/ds/LM/LM35.pdf

I'd suggest an LM35 plus an LM3914 bar graph driver.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.