Thermostat project

[lamazoid]

Hello, Gary

Recently, i'v found cheap heating cable on Aliexpress:
www.aliexpress.com/item/New-infrared-heating-floor-heating-cable-system-of-3mm-Silicone-carbon-fiber-wire-electric-floor-hotline/2054057218.html

And i decided to use it in warm floor system. So i propably need a thermostat.
But available thermostats are expensive and has functions which i don't need, like timer programming by days of week.
I need something simple, just to turn on and off by a given threshold.

I found your project, which seems to be suitable for that:

chemelec.com/Projects/Temperature-Sensor/Thermostat.htm

thing, which i don't quite understand, is the use of 1n4148 as temp sensor.
can you explain that?
also, for what actual temp range you have used this circuit?

[Gary Lecomte]

This Circuit I show is for 110 VAC.
So if your using 220VAC, you will need to make some Modifications, especially to the Non-Isolated 12 Volt Regulator.

Diodes change their Forward Voltage Drop as their Temperature Changes.
*** About 2 Millivolts per Degree of temperature.***
So using 4 or 5 Diodes in Series, it will change 8 to 10 Millivolts per Degree.

I used 1N4148 Diodes in the Circuit, But 1N4001 or 1N4005 Diodes are also Good.

To Check This Out, Put a single Diode on Test, using a Multi-meter that has a Diode Test Function.
Than apply some Heat or Cold to the Diode and you will see a Definite Change in the reading.

This circuit has a considerable Range of temperature, but you can easily change the Potentiometer values to make it more suitable for your application.

In Canada, These Heated Floors also require having Numerous, Spaced Thermal Cut-Off Switches Embedded in the Floor to turn Off the Current in the Event of HOT SPOTS.
Example: If a small Carpet or other Items are put on this heated floor, the Temperature under that part of the floor will Get HOTTER than the uncovered parts.

[lamazoid]

Sept 28, 2016 5:42:58 GMT -8 Gary Lecomte said:

This Circuit I show is for 110 VAC.
So if your using 220VAC, you will need to make some Modifications, especially to the Non-Isolated 12 Volt Regulator.

Diodes change their Forward Voltage Drop as their Temperature Changes.
*** About 2 Millivolts per Degree of temperature.***
So using 4 or 5 Diodes in Series, it will change 8 to 10 Millivolts per Degree.

I used 1N4148 Diodes in the Circuit, But 1N4001 or 1N4005 Diodes are also Good.

To Check This Out, Put a single Diode on Test, using a Multi-meter that has a Diode Test Function.
Than apply some Heat or Cold to the Diode and you will see a Definite Change in the reading.

This circuit has a considerable Range of temperature, but you can easily change the Potentiometer values to make it more suitable for your application.

In Canada, These Heated Floors also require having Numerous, Spaced Thermal Cut-Off Switches Embedded in the Floor to turn Off the Current in the Event of HOT SPOTS.
Example: If a small Carpet or other Items are put on this heated floor, the Temperature under that part of the floor will Get HOTTER than the uncovered parts.

I understand all of this, i meant a slightly different thing.
Because temperature drift of diodes is a semi-documented feature, and does not belong to the family of diode's key parameters, is it really stable from part to part?
I mean, can you once tune the circuit according desired application (e.g. temp range) and then just replicate it, without tuning each one?

[Gary Lecomte]

It isn't so much the Diodes being a problem, but more likely variations in the 4049 can be a problem.

But If the Diodes and 4049's have the SAME BATCH Number, than less likely to be a problem.