Timed Status Indication w/ Multicolor LEDs

[jonny578731]

I need some help from you experts out there.  I am constructing a prototype mechanical device which needs a process status indicator.  My goal is to have a green led illuminate when master power is activated, a red led while power is applied to heating coils (for a certain fixed time say 10 s.) and then a yellow led to illuminate for another 20s or so after the heating coils have stopped receiving power (to indicate that the machine is still cooling and unsafe to touch).  After the preset time has expired, I would like the green led to turn back on - indicating machine is prepared for another cycle.

Does anyone have any words of advice or suggestions for an engineer who is fairly inexperienced with electronics?  Thanks in advance for any help that you can provide.

[EdwardM]

Hi jonny

your requirement should be fairly easy to satisfy...

It can be done in a number of ways, for example, a microprocessor (PIC or other) can with suitable circuitry, detect the presence of master power and illuminate a green LED, likewise it can detect the presence of current in the heating coils and light a red LED and when that current disappears, illuminate the yellow LED for any given time, it isn't difficult to do if you have the right equipment.

I don't know where you are geographically but I would have thought that this is the kind of project that a local high school or college may find interesting for its students

Best of luck

Ed

[Guest 2old4digital]

Yep;  a little more info and someone in this place might draw your diagram for you.  Like what is the voltage and how many switch's are used to operate your device, would be helpful, give it some thought and let everyone know. Good luck

[boombar]

No need for microcontroller.

Make detection when heater is on and off (comparator?)

1. When heater is on, signal from comparator powers red half of the LED, and keep green half off via inverter.
2. When heater turns off, red goes off, and green turns on. This signal drop trigers 555 which again keeps red led on for next 10-20 sec. In this case both lights are on, and LED glows orange.
3. After 555 times out, it turns red off, but green stays on until next cycle.
And all over again.

Only problem is how to triger 555 (monostable). Since trigger pin needs ti go low to start 555 and back high before 555 times out, if not, out pin will stay high forever.

Maybe a capacitor could be connected to trigger pin of 555 like this:

[jonny578731]

Yep;