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 !!!!