Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Air Conditioner without using Microcontroller or Arduino

E

elektrikmuhendisi615

Newbie
Joined
Jan 2, 2024
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
18
Hello, we were asked to make an air conditioner using only BJT, MOSFET, Op-Amp, resistor, capacitor, and LM35 sensor, without using a microcontroller or Arduino. However, I don't know how I can do this in an analog circuit without any controller. In the project I want to do, the air temperature must remain between 24 and 40 Celsius, and if the air temperature is outside this value range, the fan or resistor must work automatically to bring the temperature to this range. Can you help me? Are there any resources or circuit suggestions you can recommend to do this?
 
Sort by date Sort by votes
LM35 measures the temperature,
Op-Amp can be wired as a comparator, (although a real comparator would be better)
Op-Amp output drives the transistor to operate the fan.

Look up "voltage comparator" to see how to wire it up.

Brian.
 
Upvote 0 Downvote
betwixt said:
LM35 measures the temperature,
Op-Amp can be wired as a comparator, (although a real comparator would be better)
Op-Amp output drives the transistor to operate the fan.

Look up "voltage comparator" to see how to wire it up.
Click to expand...
Thank you for the information, could you send an example of this circuit if you have any? I understand what you say but I can't image how I can design.
 
Upvote 0 Downvote
Use hysteriesis on comparator to get the range window :

1704233483234.png


The hysteresis will allow the fan to come on and drop T by window width and
then tuirn off and allow T to rise window width before turnimng oin fan.

Sim this in falstad..... https://www.falstad.com/circuit/


Regards, Dana.
 
Upvote 0 Downvote
once you get that working , for extra points ,make the fan proportional speed control by the duty cycle of
elektrikmuhendisi615 said:
Hello, we were asked to make an air conditioner using only BJT, MOSFET, Op-Amp, resistor, capacitor, and LM35 sensor, without using a microcontroller or Arduino. However, I don't know how I can do this in an analog circuit without any controller. In the project I want to do, the air temperature must remain between 24 and 40 Celsius, and if the air temperature is outside this value range, the fan or resistor must work automatically to bring the temperature to this range. Can you help me? Are there any resources or circuit suggestions you can recommend to do this?
Click to expand...
--- Updated ---

Start by writing a list of interface requirements for your design spec.
  1. Input = 24 to 40 C on LM35 is 240mV to 400 mV is desired operating range. Do not exceed this temp. And define fan control driver using 3W 5V fan.
  2. Two choices
    1. Hysteresis slow on & off from 40 deg Fan On to 35 deg OFF
    2. Hysteresis fast on & off using 100 Hz Hysteretic clock or so using temperature voltage controlled duty cycle of 20% to 100 % from 30’ to 40’C assuming 0 to Vdd using R2RIO OpAmp. Define Osc and amplifier gain&offset next.and choose Vdd and fan to be the same.
    3. Let’s use single 5V =Vfan=Vdd. So if input is from 400mV - 300mV for output 5V to 0V then the gain is 5V/100mV =50 and the offset Vref using a gain of 50 x 300mV to start fan at 0V is 1.5V But BLDC fans need 10 to 15% to get started and if stalled may get hot of internal FET driver until is starts moving. So let’s say 20% duty cycle or 1V avg . Next design fan driver using a low side switch good for 10x the current needed to stay cool. For stall starting use 0 to 5V control. For simpler concept…
    4. A muffin fan is approximately R=P/V^2 so choose a logic level FET with RdsOn of that dissipates only 0.1W max. Vgs(th) max must be < 1/2 of 5V or 1.2 to 2.5V or less. Next design the DC controlled oscillator with 0 to 5V 0 to 100% for about 100Hz
    5. With RC negative feedback = T = 1/2f =5 ms then use 50% hysteresis for +V feedback to Vctrl or Rin=Rfb. Next you disable the fan if PWM<20% or 32 deg C which is 20% of the 30 to 40’C linear control PWM range either by comparator, diodes or ignore this for now as this is non-linear control design.
    6. Make a block diagram with these I/O metrics for test verification on each stage.
    7. Put it all together into a schematic with signals drawn on it
  3. I may help get you started with the CMOS PWM oscillator if you fail to find one
  4. Get busy
 
Last edited:
Upvote 0 Downvote

LaTeX Commands Quick-Menu:

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top