Need a basic circuit that will turn on and off a DC transistor relay but only when the secondary voltage reaches a set value and will turn off the relay when it drops below the voltage.


The circuit will be 12v (for a car)
I have 12volt and neg coming directly from the battery.

12V --------------- Relay (Normally Open) Relay Out ------------- LED Light Pos.
Neg ----------------------------------------------------------------------------- Led Light Neg

Relay Control has + and – input and will trigger relay at .03 volts. Circuit can handle up to 42 volts DC.

Here is the problem.
I have second 12v DC pulse generated source as the input to the circuit.
It averages about 6V on a analog meter but is a 0 to 12 square wave. That varies in duration so it run in two modes low speed and high speed.
I need circuit to sense that when it changes the pulse to high speed (less off condition) so it will trigger the relay.
I want to turn on the relay when the voltage average exceeds 7 volts (analog reading) and turn off when below set value Would be great if it can be adjusted.

The positive pulse coming increases by two so the on state is twice as long (creating 10v if measured by analog) The problem I'm having if finding a way sense low pulse from high pulse condition.

I have no problem compensating for a working solution.

 

If it is the same pulse but at a higher rate, you could set up a 555 to operate at as a missing/pulse pulse/presence detector as the pulse interval will change.
Max.

 

You might mimic the analog meter with a RC filter followed by a V comparator. Values depend on pulse rate.

 

If varying rate/interval of pulse, I recently made up a 556 timer to detect a sprocket low speed detector, also a 8pin micro version which could possibly be adapted.
Max.

 

If it is the same pulse but at a higher rate, you could set up a 555 to operate at as a missing/pulse pulse/presence detector as the pulse interval will change.
Max.

It is the same pulse at a different rate.

 

You might mimic the analog meter with a RC filter followed by a V comparator. Values depend on pulse rate.

Can you share what the circuit would look like?

 

It is the same pulse at a different rate.

Then the 556 or pic circuit would work.
Max.

 

What is the frequency or repetition rate of the pulse signal, and does it vary? This is critical information. Also, how fast must the circuit respond to the changes in the input signal?

ak

 

Need a basic circuit that will turn on and off a DC transistor relay but only when the secondary voltage reaches a set value and will turn off the relay when it drops below the voltage.


.

Window comparator.

 

I can't seem to come up with a solution that is frequency independent, close might be driving an incandescent
lamp , output is detected with LDR ? Need answer to post # 8.

 

Need a basic circuit that will turn on and off a DC transistor relay but only when the secondary voltage reaches a set value and will turn off the relay when it drops below the voltage.


The circuit will be 12v (for a car)
I have 12volt and neg coming directly from the battery.

12V --------------- Relay (Normally Open) Relay Out ------------- LED Light Pos.
Neg ----------------------------------------------------------------------------- Led Light Neg

Relay Control has + and – input and will trigger relay at .03 volts. Circuit can handle up to 42 volts DC.

Can you post the relay's data sheet or at least a manufacturer and part number, please?

Here is the problem.
I have second 12v DC pulse generated source as the input to the circuit.
It averages about 6V on a analog meter but is a 0 to 12 square wave. That varies in duration so it run in two modes low speed and high speed.
I need circuit to sense that when it changes the pulse to high speed (less off condition) so it will trigger the relay.
I want to turn on the relay when the voltage average exceeds 7 volts (analog reading) and turn off when below set value Would be great if it can be adjusted.

The positive pulse coming increases by two so the on state is twice as long (creating 10v if measured by analog) The problem I'm having if finding a way sense low pulse from high pulse condition.

How wide is the pulse in the low speed condition, how wide is it in the high speed condition, what's the pulse repetition rate, and how much can you afford, for parts, per unit?

I have no problem compensating for a working solution.

I have no problem with accepting compensation for services rendered so, If you can answer the questions I asked, I'll be happy to provide you with a working solution for fair compensation. Or, if it's just for your own use, for free.

 

Just a starting point ... As the pulses get wider the charge on the capacitor gets higher. The LM393 is a voltage comparator, comparing the charge on the capacitor to the trigger level, 9 V, or what ever. When the voltage on the cap exceeds the trigger level the output goes low turning the LED on.

Need a basic circuit that will turn on and off a DC transistor relay but only when the secondary voltage reaches a set value and will turn off the relay when it drops below the voltage.


The circuit will be 12v (for a car)
I have 12volt and neg coming directly from the battery.

12V --------------- Relay (Normally Open) Relay Out ------------- LED Light Pos.
Neg ----------------------------------------------------------------------------- Led Light Neg

Relay Control has + and – input and will trigger relay at .03 volts. Circuit can handle up to 42 volts DC.

Here is the problem.
I have second 12v DC pulse generated source as the input to the circuit.
It averages about 6V on a analog meter but is a 0 to 12 square wave. That varies in duration so it run in two modes low speed and high speed.
I need circuit to sense that when it changes the pulse to high speed (less off condition) so it will trigger the relay.
I want to turn on the relay when the voltage average exceeds 7 volts (analog reading) and turn off when below set value Would be great if it can be adjusted.

The positive pulse coming increases by two so the on state is twice as long (creating 10v if measured by analog) The problem I'm having if finding a way sense low pulse from high pulse condition.

I have no problem compensating for a working solution.

 

View attachment 118432
Just a starting point ... As the pulses get wider the charge on the capacitor gets higher. The LM393 is a voltage comparator, comparing the charge on the capacitor to the trigger level, 9 V, or what ever. When the voltage on the cap exceeds the trigger level the output goes low turning the LED on.

Good idea.

If I may... your circuit needs a little hysteresis so the relay won't chatter as C2 charges and discharges around the reference voltage on U1-6,



and the LM393's sinking output might be a little light to drive the relay's input LED.

 

Good idea.

If I may... your circuit needs a little hysteresis so the relay won't chatter as C2 charges and discharges around the reference voltage on U1-6,

View attachment 118437

and the LM393's sinking output might be a little light to drive the relay's input LED.

Excellent!
Does the LED interfere with this? Should we use a different stage or a transistor to drive the LED?

 

Excellent!
Does the LED interfere with this? Should we use a different stage or a transistor to drive the LED?

Yes, and yes. From TI's data sheet,


you can see that as the LM393's output stage is loaded more and more heavily, its output voltage will drop more and more, spoiling the effect of the hysteretic feedback. Depending on the relay's drive requirements, one solution might be to use the second comparator to drive the relay, while the ultimate solution might be to use the second comparator to drive a transistor which, in turn, would drive the relay's LED, like this:



BTW, I made a mistake with the earlier hysteresis connection, which I've corrected here.