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Voltage Based Switch

stallican

New Member
Hi,
I will start by saying that I am fairly new to electronics, so don't be afraid to dumb it down!

I have designed a simple solar tracking device that will track the sun 360 degrees (within about +- 1.5 degrees).

Basically, the sensors that I am using emit 3.4V which operate a motor assembly and drive the solar collector east or west.

Now I am building a much larger collector that will use 12v dc motors.

My problem: making my tracker power up the motors.

I am tying to keep this simple. What I would be ideal would be a "switch" that senses a threshold voltage of my tracker, and then switches on the motor that is wired to the 12v battery, once the threshold voltage drops off, the motor circuit is switched off.

I am aware that I can use MOSFET or IC to do this. My goal is to have this set up as simple as possible. I am in a fairly remote area and I have to order everything!!
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi,
I will start by saying that I am fairly new to electronics, so don't be afraid to dumb it down!

I have designed a simple solar tracking device that will track the sun 360 degrees (within about +- 1.5 degrees).

Basically, the sensors that I am using emit 3.4V which operate a motor assembly and drive the solar collector east or west.

Now I am building a much larger collector that will use 12v dc motors.

My problem: making my tracker power up the motors.

I am tying to keep this simple. What I would be ideal would be a "switch" that senses a threshold voltage of my tracker, and then switches on the motor that is wired to the 12v battery, once the threshold voltage drops off, the motor circuit is switched off.

I am aware that I can use MOSFET or IC to do this. My goal is to have this set up as simple as possible. I am in a fairly remote area and I have to order everything!!
hi,
Look at the datasheet for the LM393 dual comparator ic.

This can be wired as a threshold detector and the output drive a transistor or MOSFET.
 

stallican

New Member
Would I have to program this chip? It has a variable voltage comparator which can apparently be set to a wide variety of differentials. So how are the differential levels set?
 

Hero999

Banned
No you don't have to program anything.

I recommend this tutorial.
Voltage Comparators

The LM311 is also a good comparator but its a sinlgle not a dual.
 

stallican

New Member
I get the idea on this component, which leads to my next question.

If this IC outputs a binary decision, ie on / off. What must be connected to that to drive my motor? Some sort of relay switch attached to a battery maybe?

My circuit produces about 4.3 v, but little or no current. And the motor I want to drive is comparable to something that would run a power window in a car.
 

Hero999

Banned
The LM311 can directly drive a small relay ≤50mA.

Replace RL in this circuit with the relay coil and reverse parallel diode, and reverse the logic for the input pins, i.e. the relay will turn on when the output goes low.
 

mneary

New Member
Hi,
Where is a good spot to get a LM311? Anyone have a suggestion?
I would look at surplus places like All Electronics or Electronic Goldmine. Torrance Electronics should have them, too. Various vendors on ebay also have them. Price is 39 cents to a dollar.

If you want to learn more about comparators, you might consider the LM311 kit (contains 6 chips plus support parts and a tutorial) from Nightfire for under $10.
 

stallican

New Member
Thanks Hero999 for your help. And thanks mneary for the kit suggestion. I saw that over at ebay, and I was wondering if it was worth it. I think I'll buy one of those. I will let you all know how it works out.
 

Hero999

Banned
I forgto to say that it's always a good idea to connect a feedback resistor in any comparator circuit to add some hysteresis.

This helps to prevent oscillation.
 

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stallican

New Member
Hi,
I have been researching this a bit, and I have a quick question. I need something that works outside (-20 Celsius - +30 C). Will the LM211 do the same thing as the 311?
 

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