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Help with LED circuits

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zipdogso

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led circuits

Until last year when I dabbled briefly I hadn't picked up a soldering iron for over 2 decades and forgotten most of what I learned....but my recent project requires amongst other things for me to go back and do electronics again.

My problem is I need to have an LED display for the state of a fan thus:-

1./ the LED is off either the fan or something worse has gone wrong.
2./ the fan is attached to power but not rotating. (RED LED.)
3./ the is powered and running. (GREEN LED.)

To break myself back in gently I have been trying a few things on the bread board.

The schematic attached ( not a good one i admit.) is where I have got to so far and works.

On the left of the relay (as you look at it.) is a simple constant current LED driver circuit. On the right is the fan it is 12v 1.5amp 12cm. The relay is DPDT. I am running both the LED circuit and the fan from the same supply and I wanted to be able to adjust the fan input hence the constant current LED circuit.

As shown in the schematic everything works fine just for testing I also ran the relay coil off the same supply as well with a switch to turn it on and off.

BUT.....

1./ It doesn't satisfy my first fan state i.e. if the fan breaks down the LED will continue to show red or green. At the moment I can only think I will have to run the fan on the relay coil circuit with the coil going to the base of a transister and the collector driving the fan (due to the 1.5amp current draw of the fan.)and add an extra relay for the red/green states but I havent come up with anything beyond this yet.

2./ I really wanted to use 2 lead bicolor LEDs I have 3 fans to monitor, temp outputs and allsorts so I would prefer one LED display per fan.

Any ideas ?
 

aryajur

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how to use relay and leds schematic

Hello zipdogso,
Please can you explain the functioning of your schematic. What I see is that if there will be power to the relay the relay is on NO position powering the lower LED which I assume is GREEN. If the Relay is powered off then the upper LED is connected but if there is no power the LED will also not light up. I am missing something please can you explain the operation.
 

zipdogso

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bi-color led driver schematic

aryajur said:
Hello zipdogso,
Please can you explain the functioning of your schematic. What I see is that if there will be power to the relay the relay is on NO position powering the lower LED which I assume is GREEN. If the Relay is powered off then the upper LED is connected but if there is no power the LED will also not light up. I am missing something please can you explain the operation.

Since your an advanced member level 2 I find it quite amusing you can't understand how the circuit works, it is about as simple as they come....
Both leds are powered through the PNP transister with it's collector current connected to the common of the relay... if the relay coil is "off" the led connected to the NC relay terminal is lit when the relay is "on" the LED connected to the NO terminal lights. "eez simmple" as they say...

I have since found there are 3 wire bicolor LEDs in both common anode and common cathode ( I didn't realize this.) so the two LED's can be switched for the single 3 wire bicolor with the correct termination.

However I have found, through another site, that checking the fan failure is rather more complicated than I first presumed and i won't be using my schematic that is attached. Since I cannot see the fans in operation, checking fan failure is more important than can be seen from my schematic so a completely different setup will be used instead.

So basically my request has been solved on another forum.
 

aryajur

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indicate bad relay coil using an led

Well I am glad I amuse you, anyway if you read my previous post carefully I think I already mentioned that I see which LEDs are being lit up (so that does indicate that at least I understand how they are powered up), so your explanation was not useful, thing I was confused about and still am is for what conditions the circuit is working and what is missing? You said that it is working for the latter 2 cases And that is what I didn't understand as I asked you. How is it that your red led lights up when the fan is connected but not rotating. Why will the relay shift it's posiion in that case? So please read this post and be amused further if you will but please post a proper explanation.
Even if your post is solved please be courteous enough to share your solution here for others to learn also.
 

GrandAlf

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status on off bi-led circuit

You need to know if the fan is actually running, there are a few methods to determine this.

1 - Engineer a vane switch in front of the fan. Maybe swing a magnet towards a reed switch with a light spring return. You could then use a bi colour common cathode led, one anode to switch, other to motor. Two colours or off indication.

2 - Measure running motor current with comparator. Trigger for too much current (stalled) or no/little current (supply bad).

3 - Use a hall effect or opto switch on the fan. Sends out a steam of pulses to an integrator driving a relay/transistor. Or input to a cheap 8 pin micro. You could drive the leds how you wanted doing this. Good simple project if you want an introduction to micros and programming.

4 - Use a thermistor to measure airflow. May not be reliable if there are large temperature changes.

Hope some of this helps.
 

    zipdogso

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zipdogso

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how to drive bicolor led from relay

aryajur said:
Well I am glad I amuse you, anyway if you read my previous post carefully I think I already mentioned that I see which LEDs are being lit up (so that does indicate that at least I understand how they are powered up), so your explanation was not useful, thing I was confused about and still am is for what conditions the circuit is working and what is missing? You said that it is working for the latter 2 cases And that is what I didn't understand as I asked you. How is it that your red led lights up when the fan is connected but not rotating. Why will the relay shift it's posiion in that case? So please read this post and be amused further if you will but please post a proper explanation.
Even if your post is solved please be courteous enough to share your solution here for others to learn also.

If you'd read my original post you would see the the2 seperate poles of the relay are powered by the same PSU.(admittedly this is not in schematic now I think about it.)
so when the relay is "off" power to the fan which is the same source as the led circuit is "on" but the fan itself is "off" so technically it is connected but "off" which is shown by the the RED led connected to the NC terminal of the the other pole. It is a DPDT relay so both poles are switch together. When the relay is activated (by an outside circuit not shown.) both poles switch to the NO terminal, at this point the fan starts up and the LED shows green.

Now tell me if a,) that was not blindingly simple b.) satisfying the second and third states that i required.

I don't really intend to come back here for 2 reasons
a.) it takes to long to get a reply.
b.) well....I think you already know what I think relative to your reply.

Added after 17 minutes:

GrandAlf said:
You need to know if the fan is actually running, there are a few methods to determine this.

1 - Engineer a vane switch in front of the fan. Maybe swing a magnet towards a reed switch with a light spring return. You could then use a bi colour common cathode led, one anode to switch, other to motor. Two colours or off indication.

2 - Measure running motor current with comparator. Trigger for too much current (stalled) or no/little current (supply bad).

3 - Use a hall effect or opto switch on the fan. Sends out a steam of pulses to an integrator driving a relay/transistor. Or input to a cheap 8 pin micro. You could drive the leds how you wanted doing this. Good simple project if you want an introduction to micros and programming.

4 - Use a thermistor to measure airflow. May not be reliable if there are large temperature changes.

Hope some of this helps.

Hello mate...yep your on the nod.
As I mentioned in my previous post I got the reply I wanted elsewhere but since I have come back this once when I didn't really want to, you deserve an answer.

1-3 of your suggetions i got on the other site. the 4th while interesting I cannot use it. Unfortunately I am unable to place anything outside the fans so I needed a voltage/current sense solution.
Due to the fact i am a noob I hadn't considered the fact that there are 3 states of failure of a fan..hmmm.
Well I was pointed in the direction of a very simple overcurrent circuit which can be altered and then multiplied twice then amended again to give a hardwired circut that can test all three states. well no...not strictly... instead of testing for under current it just tests that the current is correct. I havent yet got round to redrawing the circuit I need yet but it's just two trimpots, 3 transistors and a handful of resisters...nothing near as complicated as a relay !!!!
 

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