Help needed for proteus PCB designing

I would point out that the 741 is almost 50 years old and not a good device by todays standards, particularly when running from supplies as low as 9V. You might find the 741 cannot provide enough base current to turn a BD135 fully on.

In the thermistor schematic, consider what might happen if the 10K variable resistor is set to minimum resistance. It could damage the thermistor and it will certainly cause some self heating. In the LDR schematic, the sensitivity to light changes is controlled by the potentiometer, is this what you really want? In most applications the sensitivity should remain high and it's the light level threshold you want to adjust. In both designs it would be more sensible to put the variable control where you have the potential divider and use a fixed resistance in series with the sensor.

The first design, if built as it is may also dissipate quite a lot of heat when the fan is running at medium speeds. The BD135 might run hot, it all depends on the fan type which you have not specified. If you can change to a PWM design it would be far more efficient.

Brian.

Hi,

My saying: A circuit without a capacitor is no circuit (in the meaning of reliable operation)

In both circuits I see some issues:
* no power supply decoupling
* no noise filtering
* 741 is about 55 years old. I´m designing electronics for more than 30 years now ... and from my beginning the 741 was outdated. I never used it. Still you are free to use it.
* you say "smooth control", but I see no feedback at the OPAMPs, thus it´s more working as a ON/OFF comparator with a huge likelyhood to oscillate
* linear control generates heat ... usually fan control is not wanted to generate heat
* 9V block battery to drive a 2.3V LED .. is a big waste of batteries. Better use 2x or 3x AAA (or AA) size and get much longer life time with lower cost.

**
There are ready to buy fans including temperature control, with very low heat generation. They usually also include stall protection to avoid power consumption and heat when the drive signal is too low for the rotator to move. Also they usually include some kind of kick start to avoid friction problems.

***
I recommend to do an internet search for both topics. You will find thousands of good designs.

Klaus

betwixt said:

I would point out that the 741 is almost 50 years old and not a good device by todays standards, particularly when running from supplies as low as 9V. You might find the 741 cannot provide enough base current to turn a BD135 fully on.

In the thermistor schematic, consider what might happen if the 10K variable resistor is set to minimum resistance. It could damage the thermistor and it will certainly cause some self heating. In the LDR schematic, the sensitivity to light changes is controlled by the potentiometer, is this what you really want? In most applications the sensitivity should remain high and it's the light level threshold you want to adjust. In both designs it would be more sensible to put the variable control where you have the potential divider and use a fixed resistance in series with the sensor.

The first design, if built as it is may also dissipate quite a lot of heat when the fan is running at medium speeds. The BD135 might run hot, it all depends on the fan type which you have not specified. If you can change to a PWM design it would be far more efficient.

Brian.

Click to expand...

thanks for the valuable information in above you said 741 is old then what type of op amp i can use for these tasks
i don't want to control the sensitivity of the light bulb by the the potentiometer, i need to control the sensitivity by the LDR
what changes i have to made in above two circuit
and also how can i combine these two circuits into one circuit

You can use almost any kind of dual op-amp but look for one that works on 9V or less and preferably one that can reach rail-to-rail output. Another old but still manufactured one is the TL072 or TL082 which should work far better than a 741. Instead of a BD135, see if you can find a darlington transistor, they do have some disadvantages but their base current will be far less so the op-amp will drive it directly.

It isn't clear whether you want the fan and LED to turn on and off or their speed/brightness to be variable. If you want them to simply turn on or off at a set temperature or brightness, consider using a dual comparator IC instead of an op-amp. Comparators do not have a linear output characteristic, the output is either high or low depending on the difference in input polarities.

Brian.

betwixt said:

You can use almost any kind of dual op-amp but look for one that works on 9V or less and preferably one that can reach rail-to-rail output. Another old but still manufactured one is the TL072 or TL082 which should work far better than a 741. Instead of a BD135, see if you can find a darlington transistor, they do have some disadvantages but their base current will be far less so the op-amp will drive it directly.

It isn't clear whether you want the fan and LED to turn on and off or their speed/brightness to be variable. If you want them to simply turn on or off at a set temperature or brightness, consider using a dual comparator IC instead of an op-amp. Comparators do not have a linear output characteristic, the output is either high or low depending on the difference in input polarities.

Brian.

Click to expand...

thanks for the valuable information can anyone provide the circuit diagram that, control the room fan speed (rpm) by the temperature of the room and control the room light (on/off) by the room light intensity using the thermistor and LDR and opamps (simple circuit is needed) for the university mini project

Generic usage of thermistor with op amp. Stable reference voltage is provided at one input. Thermistor resistance rises and falls. Adjust resistor value (or volt level or both) so that thermistor temperature triggers op amp to change state.

I am sharing some tutorials on how to design PCBs in proteus. I hope they will help you at least to some extent.

https://www.pcbway.com/blog/PCB_Design_Tutorial/How_to_Design_PCB_in_Proteus_1.html