Hello all,

I have a few questions after having tried to achieve with various circuits - without a micro-controller - and also various circuits with an arduino uno as micro-controller, but with my limited knowledge of electronic motor drives, and my source for the circuits designs being from various random places ( about a dozen ) found online etc.

I still have not found a solution, and have spent many hours trying.

So hopefully you more experienced persons can help!

And yes I have been identifying the type of mosfet And pin outs etc before trying them, maybe an OpAmp is more suitable? I have not tried one.

need a circuit diagram showing how to---

1. Drive a small 12 volt DC motor (typical brushed type , like in a common battery operated drill)

2. Using the minimum amount of components and preferably no micro-controller being included in the design.

1. Have the load/ motor receive its power as a result of the amount of light being received by an illuminated light dependent resistor. ( light source circuit is separate and not needed in this design)

4. Have this power be modulated in such a way that full illumination gives the motor full power , no illumination gives the motor no power,

And every step in between ( various light levels) could be described as a smooth ramp from 0 to 100 % depending on the amount of light on the LDR.

I have only tried this with a few different mosfets and an arduino, but just can't seem to make it happen,and also I am still confused as to proper wiring to the mosfet ( if used for this purpose and not as a high power switch only)

I really appreciate any help, Thanks!

 

The NE555 timer chip can be configured as a PWM generator using a LDR.
The output from the 555 can trigger a mosfet to control the motor.

 

The only problem here is the definition of "Dark", and the definition of "Light".

You need to start with the Voltage of your Power-Supply.

Next find a Light-Sensor that can be implemented into a Circuit that will
vary the Circuit's Output-Voltage from around 1/3 to 2/3 of the Power-Supply-Voltage.
The rest is very simple.
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I am still confused as to proper wiring to the mosfet ( if used for this purpose and not as a high power switch only)

Using a MOSFET to control a motor IS using it as a switch.

You pick an interval of time, say 1 msec. Then in each interval you turn the MOSFET on for a fraction of that. Say 500 usec, which would be half power.

This is what is known as PWM.

 

Thanks to all 3 of you,

sghioto- the use of a 555 for pwm to the mosfet is something I had come across but the output / load power in the circuits as seen could not handle a 12 volt motor only smaller loads. Any ideas or a reference schematic?

Lowqcab -- the power supply is a 12 volt dc
I am no good at electronic equations -ex how many ohms spec. for the LDR that would be a good fit for the 12 v supply and 12 volt motor.

Bobtph- I thought ( probably wrong ) that a mosfet could be used like a rheostat a little power to the gate ,a little to the load, more to the gate more to the load
without the use of pwm ,or do all mosfets require a pwm signal to ramp up and down (I was thinking of using just a pot as a baseline , the LDR and a few other misc. components?
again probably wrong?

 

sghioto- the use of a 555 for pwm to the mosfet is something I had come across but the output / load power in the circuits as seen could not handle a 12 volt motor only smaller loads. Any ideas or a reference schematic?

The power handling is in the proper selection of a mosfet that can handle the load.

 

A FET can be used as a crude Pot, but it will be seriously Non-Linear in response.

To design a Circuit like this REQUIRES figuring-out the Math,
and understanding Specification-Sheets.

This Project will require at least one Op-Amp, and a handful of Passive-Components.

What end-result is this project supposed to accomplish ?
Why do You want to build it ?
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Sghioto thank you,

If you are as old as I am , you may remember the source of this circuit.

Can this circuit be used to achieve my goal assuming I chose a suitable mosfet as you have recommended, and if it would work ,exactly where and how would the LDR be placed in this circuit, and or replacing any existing components on the schematic?

as much detail as possible would be appreciated

 

The project will be used as a cooling fan -with the amount of air being pushed by the dc motor with fan blades attached, based on the amount of sunlight present at any time of day, so a simple common on or off phototransistor/ photocell dusk to dawn type of circuit will not suit the application.

Any help on the questions related to the uploaded schematic above would be greatly appreciated

 

If you are as old as I am , you may remember the source of this circuit.

If that circuit is from a Forest Mims notebook then the answer is yes.
Here's a version used in another project as a starter.

 

I guess you know the fan will require more current at initial start-up than when running at the desired speed.

 

Sghioto you are correct my friend! Mims it is.
I will give your revised circuit a try, thank you so much
great help much appreciated!

 

What are the Current-Specifications of your "12-Volt" Power-Supply ?

What are the Current-Specifications of Your "12-Volt" Motor ?
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Wouldn’t running the fan based in temperature be preferred over running it based on light?

You can use a varying voltage to control fan speed, and you can use a MOSFET to vary the voltage, but PWM is preferred for many reasons.

 

I vote Temperature-Control also.
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It is always nice when anyone is interested expanding their horizons and learning new things.
But some things are not always so simple.
Food for thought literally . ( see included links to papers)

HTTPS://.plantcare.https://plantcare.wisc.edu/wp-content/uploads/sites/213/2015/02/Light-and-Temperature2015.pdf.edu/we-content/uploads/sites213/2015/02/light-and-tmperature2015.pdf

https://link.springer.com/article/10.1007/s00344-021-10337-y

 

It is always nice when anyone is interested expanding their horizons and learning new things.

What is it you expect us to learn from those links? How does anything in them relate to controlling fan speed based on light level?

 

Given your inability to find and or design a suitable circuit I would wager that learning and using an Arduino will get you to your goal faster, than what you are doing now. I understand your reluctance, but you need to approach this process with an open mind.

 

Circuit with CMOS timer and photodiode.
For the initial push, you need to add a diode and a much larger capacitor to the capacitor.

 

Welcome to AAC.

Could you explain why you are using a light sensor to control a fan intended to manage temperature?
Why wouldn‘t you use a temperature sensor? There can’t be a constant relationship between light level and temperature disregarding the ambient temperature and sky conditions.