Sensing temperature difference

Projects General Guidance
1

One of my current projects is replacing the failing tile floor of a shower stall. The tile is now gone and I made a fiberglass pan to rest upon the remaining Durock floor. In the pan is a deck made from synthetic planks. Beneath the deck I will be installing a ring of a UV LED waterproof lighting strip. The strip being controlled by an ATtiny85. My plan is that the MC will look at two inputs. One input will be looking at the temperature of the copper pipe supplying the shower head. The other I'm not quite firm about. My thinking now is to hang a short section of dummy pipe in the cavity that the pipe supplying the shower head is in and have the other input look at the temperature of the dummy pipe.

My theory is that normally the two pipes will be at or near the same temperature. I can't imagine that during a shower, the pipe supplying the shower head would not be above the temperature of the dummy pipe. So when it is, energize the LED strip. When the shower is finished it'll take some time for the pipe supplying the shower head to cool to the same temperature of the dummy pipe. This works in favor of the scheme since I would like the LED strip to remain on for some time after the shower is finished. Naturally some hysteresis will be incorporated.

Seeking some input on my plan. Is there a potential fault/problem? Perhaps a better method?

Also seeking advice on temperature sensing components to use. Since there's no precision involved I'm thinking simple would be good but I have no idea of what device to use.

Thanks - Scotty

2

Here's a selection of temperature sensors: Temperature - SparkFun Electronics

Looks like the TMP36 is the cheapest and very easy to use. It puts out a voltage proportional to the temperature. They are so cheap I'd consider hooking them to the Hot input to the valve, the Cold input to the valve, and one hanging in the air. That should be enough to reliably detect water flow.

3

why not just use temperature of the pipe ?

even without any calibration, it should be withing about 5 degrees of the actual temperature.

then use RGB LED's to be blue for cold, then change to red and maybe blink ?

then after X minutes, do a blinky dance of colors. saying you are taling a long shower.

you can log your last showers to get an average temperature and set a point that would allow you to chage red or blue to show if it is colder or hotter than 'normal' that way you can adjust before you get into the shower.

keep going...
add a slew of vavled. need to have a way to balance flow so that there is no flow change.
then control hot and control cold to achieve a pre-set temperature.

need some sort of switch to allow you to change or overide settings.

keep going....
height or weitch stensor. set the temp settings based on who is using the shower. I trust that the users are not all the same height or weight......

4

Hey dave-in-nj, K.I.S.S.. :slight_smile:

Thanks John, I'll have a look. I suppose there are a dozen ways to monitor the flow. Two dozen if you ask Dave.

  • Scotty