build a thermostat

Status
Not open for further replies.
A

AMIRAAM

New Member
Hello
I don't have an electrical or electronics engineering but i know some basics about electronic

I'm trying to build a thermostat please help
i want to add capacitors on this diagram, can you tell me where and why please
 

Attachments

  • THERMOSTA05.png
    30.4 KB · Views: 284
AMIRAAM said:
Hello
I don't have an electrical or electronics engineering but i know some basics about electronic

I'm trying to build a thermostat please help
i want to add capacitors on this diagram, can you tell me where and why please
Click to expand...

hi, could you tell me why you want to add additional capacitors?

Without more information, I can only suggest that you print out the schematic tape some colorful capacitors to each corner.
 
AMIRAAM said:
i want to add capacitors on this diagram, can you tell me where and why please
Click to expand...

That sounds a little difficult to respond to because you are literally saying that you want to add something and you are asking how and why.

So, I am looking at the circuit and it looks simple enough for me to understand. You have a comparator with two voltage dividers as inputs. One input is dependent on a thermistor's resistence (i.e., the temperature) and the other is dependent on the setting of a pot. When triggered, the comparator operates a relay that turns on the heating element (the resisters inside the circle. There are also a couple of LEDs

You have three capacitors on the power line.

Others here will know more, but there are only two places that I see: One is at the comparator Vcc to ground (again, you already have three smoothing the power supply. The other is across the relay coil. You have a diode there, which is appropriate but I have seen RC snubbers used as well (search terms - RC Snubber relay noise suppression).

Maybe I am missing something, but that is what I see.

You will get a better response if you provide more information.....where did that schematic come from? Why do you think you need to add capacitors? Homework assignment or what?
 
hellow gophert, dr pepper , DrG

thank you for help

gophert said:
hi, could you tell me why you want to add additional capacitors?
Without more information, I can only suggest that you print out the schematic tape some colorful capacitors to each corner.
Click to expand...

i should say : I want to add or remove capacitors on this diagram, can you tell me where and why please !?

like dr pepper said :
The thermostat is for the egg Incubator; a comparator lm339 with two voltage dividers as inputs. One input is dependent on a thermostat’s sensor (thermistance NTC for 37 °C) and the other is dependent on the setting of a pot (reference for 37 °C). When triggered, the comparator operates a relay that turns on the heater resistor


dr pepper said:
he parts in the circle are resistors, are these what you mean?
Click to expand...

yes it is heater resistor

DrG said:
You will get a better response if you provide more information.....where did that schematic come from? Why do you think you need to add capacitors? Homework assignment or what?
Click to expand...


I don't have an electrical or electronics engineering but i know some basics about electronic, while i am searhing on google i found a lot of schemas , they add two type of capacitors : the polarized and non-polarized capacitor
can i replace a polarized capacitor with non-polarized capacitor !?

please tell me why you add each capacitor and why and also their values are they correct or no !?
 

Attachments

  • THERMOSTA05 01.png
    31.9 KB · Views: 266
The capacitors on the drawing are all 100uF, and they all connect to the same point, this might seem confusing.
It is however where they are positioned that is important, each capacitor decouples a section of the circuit, and should be placed close to that section of the circuit.
This is because of the pcb tracks & wiring resistance affecting the circuit.

You can replace a electro with a non electro so long as the voltage ratings etc are the same, although for 100uF a non electro would be very large.
 

And non-existent

If we're really been picky on the circuit, it certainly doesn't need four 100uF on the supply - I would suggest a 100uF on the incoming power, and a 1uF across the comparator, and leave the others out. The circuit presumably wasn't designed by anyone who knew what they were doing, and used pointless overkill on the decoupling.
 
hellow
thank you for help

i modfied the diagram ,please see it

another thing :
The led2 is on when the heating system is on, I want to add a led 1 to be on when the heating system and the led1 are off. Please how can I do that?



 
Last edited:
Add the LED1, with a 1k series resistor, between the relay's NC pin and GND.
 
You could modify the right-hand side of the circuit like this:

Note: I haven't shown the capacitors. The LED colours are arbitrary.
 
thank you very much , I'm so happy , I had taken a long time searching for this sollution
so i modified the diagram as you suggest :
i want to give me your opinion for another thing please :
in my old diagram there was a voltage divider like is shown (red cercle) , i want to keep it if this is possible :

 
Last edited:
Hello lec_t

thank you very mutch

alec_t said:
Why the voltage divider?
Click to expand...

i want to replace the PNP Tr by NPN Tr (red cercle)
i don't know , i think that it would be better with the NPN , also by the voltage divider ,i can have good control for the NPN Tr ! ?



but please i want from you to give me another way to do this :
on my old diagram the hysteresis was done by big resistor (red ligne)
please are there any other method for this (for example a voltage divider ) because i don't like to use a this big resistor

 
What do you mean "big"? High value resistors are generally very small in physical size (or the same physical size as any other resistor) because very few amps can get through them so very little wattage. I've never heard of anyone being concerned with using high-value resistors when a high value resistor is perfectly suited (needed) for the circuit.
 
For the above circuit with the NPN transistor:
1) The R8/R6 potential divider will prevent the NPN transistor from switching off. You can replace R6 by a short-circuit.
2) Depending on how much current your relay coil draws, R8=10k is probably too high a value. I'd suggest no more than 2.7k.
3) Without hysteresis the relay will probably 'chatter'.
4) Going from a PNP to an NPN means the switching logic is reversed. To compensate, you can connect the heating element to the relay's NC contact instead of the NO contact.

AMIRAAM said:
i don't like to use a this big resistor
Click to expand...
The 'big' resistor is the same physical size as the other resistors. What is your objection to its use? This is the usual and simplest way to provide hysteresis.
 
hello
thank you again
i will keep the diagram as you suggest with the PNP :




but please another small question :
why the voltage divider is not good way : ( i will keep the PNP)







 
You seem to be obsessed with voltage-dividers . Yes, your latest PNP versions will work with a voltage-divider, but what advantage do you think it provides? I see it as an unecessary complication rather than an advantage.
 
alec_t said:
You seem to be obsessed with voltage-dividers . Yes, your latest PNP versions will work with a voltage-divider, but what advantage do you think it provides? I see it as an unecessary complication rather than an advantage.
Click to expand...

The professor said his design must have at least 10 components? (Just guessing)
 
hello
thank you again

I know two or three things about electronic, the voltage divider is one of these things

A natural science teacher gives his students two paragraphs, one about the elephant and the other about Earthworm, the next day the teacher asks one of his student, what is an elephant, the student said: the elephant is a big animal, it has a nose like the Earthworm and the Earthworm is small animal, it has ......... and he completing by the paragraph about the Earthworm because he read only the paragraph about the Earthworm

That’s why I seem to be obsessed with voltage-dividers
thank you very much
 
Status
Not open for further replies.

Similar threads

  • Question
Assistance in building a moisture probe and circuitry
Replies
0
Views
1K
chopnhack
V
  • Question
Wanting To Build Solar Street Light with Multiple Features
Replies
11
Views
5K
shokjok
S
F
  • Question
Need to design and build 250W BLDC inverters for drones
Replies
2
Views
2K
Papabravo
W
  • Question
Building a quantized sequencer without programming (MC)
2
Replies
28
Views
7K
liamjerr
L
A
  • Question
Help putting together some off the shelf low voltage heating components
Replies
5
Views
2K
abapper
A
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…