Temperature Sensor

[anitaburcher]

For a project for my college course I would like to build a unit that will beep at different tones depending on the temperature of water. This unit is to be put in the bath, so that blind people are able to tell the temperature of the water with out injuring themselves. However I have struggled to find a simple circuit that will work. Can anyone help me?

 

[Optikon]

For a project for my college course I would like to build a unit that will beep at different tones depending on the temperature of water. This unit is to be put in the bath, so that blind people are able to tell the temperature of the water with out injuring themselves. However I have struggled to find a simple circuit that will work. Can anyone help me?

Thermocouple front end.. you can place the thermocouple into your probe that will be submerged. You will need an amplifier. Compare temperature to a couple of reference voltages (comparators). which-ever temperature "window" comparator gets triped drives a switch that will change a passive network that determines buzzer frequency.


You can probably even use a low pass filtered 555 astable and change frequency by switching in parallel capacitors on the timing cap. then Low pass filter the output which will goto your speaker driver (audio amp?)

Rough first pass idea... someone else may come up with a better way.

 

[JohnBrown]

Cheap buzzers or piezo sounders can be very confusing as far as different pitched tones are concerned, because of harmonics and resonant frequencies. Also, it sort of assumes that all blind people have perfect pitch, and I don't think this is the case. I think you'd be better off with a device that bleeps a certain number of times to signify a certain temperature. I'd use a microcomputer, but then I use microcomputers for everything.

 

[audioguru]

Hi Anita,
I was thinking about suggesting that you use an amplified LM34 temp sensor mounted in a probe that would feed a CD4046 Voltage Controlled Oscillator, but you should do your own school research and maybe a blind person couldn't use it anyway.

If I blindfolded you, then asked you to jump into water that might be boiling or freezing, but that you had a beeper with a tone that changes with temperature? Would you get in after hearing the tone? Of course not!
It might make a high pitch tone. How high is high? Or it might make a low pitch tone. How..., you know.

Unless the blind person has "perfect pitch", like very few musicians have (the ability of their brain to identify the exact frequency of a tone, something like the way that you see colours), their hearing won't have a reference to base the frequency of the tone against.

I made an alarm system for the government. One alarm beeped a low frequency slowly. Another alarm beeped a high frequency quickly. See, in addition to the frequencies being completely different, I made the beep rate also different. Can't miss it: hummmmm, hummmmm, hummmmm, or squeak, squeak, squeak, squeak, squeak. They complained that both alarms sounded the same!

 

[chemelec]

An XR4151 can go an Extreme Frequency Range for a Very Small Change in Voltage.

It could easily be set for a Zero hz at say 70 degrees, and at 3000 hz for 100 degrees. Just as an Example.

Therefore Perfect pitch would not be Necessary.

 

[audioguru]

I have never used Exar ICs. I thought that they stopped making analog ICs and "went digital" years ago.
Their XR4151 is probably similar to National's LM331 V to F converter, which is still in production. Its pulse width changes extremely with frequency change, so it might need a pulse-stretcher or divider to be heard properly.
If zero Hertz is at 70 degrees F, then 3KHz at 100 degrees F (nice and warm), but would be 5Khz at 120 degrees which burns you, and you will need "perfect pitch". Narrow the range by making 100 degrees produce a low frequency and 120 degrees a high one, and hope that the blind person doesn't work for the government!

 

[-=GST=- Nemisis (cs/cz)]

could u use a thermosistor (temparature variable resistor) to connect to an astable then have a pic program to make higher pitched beeps depending on how fast the 555 was oscillating?

 

[audioguru]

Horrors!
An uncalibrated thermistor instead of an accurate temperature sensor IC?
A pic that is used only to turn the 555's tone on and off?

Why not use a microcontroller to speak the temperature or warning?

 

[Optikon]

Horrors!
An uncalibrated thermistor instead of an accurate temperature sensor IC?
A pic that is used only to turn the 555's tone on and off?

Why not use a microcontroller to speak the temperature or warning?

What ever ends up getting dipped into bath water should take into consideration the fact that the water is probably pretty "hard" and thus
conductive to some extent. Would be nice to use something that didn't involve hermetic water-tight sealing.

 

[Oznog]

A thermocouple is absolutely not appropriate for this job.

You need a thermistor. There are digital probes and temp references, but you don't need the accuracy and it's hard to get them in immersible pkgs. You'd also want an external probe to be 2-wire. Lots of cheap thermistors available in immersible pkgs.

The alarm can be as simple as a level comparator. You also want to look at what happens if the water infiltrates the pkg and either corrodes open up the thermistor leads or shorts around it.