Limit Switches with LED's

[Shinobiwan]

Okay, attempt #2...

Sick sick drawing skills there Robin!

[Jonathan]

If you're happy with just one colour LED - i.e. red when the switch is pressed, off otherwise, which basically tells you the same thing as having red/green, then it's a lot simpler. Just put an LED with series resistor in parallel with each switch.
Since you will use normally closed switches, when the switch is open (pressed) the supply voltage to the switches is now present across the switch, so will light the LED. If multiple switches are pressed, the same is true except the voltage is now divided by the number of switches that are pressed so the LEDs would be dim, hence you need to choose the resistor values carefully. If you're happy with that limitation then this is a simple solution to implement, but for the sake of one extra component Robin's solution is better.

You could instead do it in software - make a box on the gui turn red/green for each switch.

[Robin Hewitt]

If you're happy with that limitation then this is a simple solution to implement

Good try, but what happens if two switches open?

Will 2 diodes and two resistors all in series sink enough curent to switch the Bob?

How about three?

Edit: I'm not explaining that very well am I? You aren't actually breaking the circuit, you are still requiring current to flow and light the LED's.

[Jonathan]

Edit: I'm not explaining that very well am I?

No, perfectly well.

I put this diagram in the previous post, but immediately deleted it as I realised the problem you mentioned:

If V=5V, then when one switch is pressed the voltage at the node the breakout board is connected to will be the forward voltage of the LED, so about 2.1V, plus the voltage of the resistor. As you say that's probably acceptable with just one switch pressed, but still more susceptible to interference and probably not going to work with more.
We can fix this by increasing V, to say 24V, and connecting the breakout board via an op-amp used as a comparator. Set the threshold of the comparator to be just under the voltage present when one switch is pressed, then any number of switches are pressed the comparator output will switch. I guess that does loose the simplicity...I'd do it your way, except I don't really see the point of adding LEDs!

[manofgresley]

Hi Jonathan
Thanks for all your help, seems like i was asking for quiet a lot when i said simple. Forgive me but you lost me at OP AMP / Comparator, and can you explain what a gui is from a previous post?
This is my latest interpration, do you think it will work, i realise that the only LED to illuminate will be the one on the activated switch.

Regards and Thank You

Ray

[Robin Hewitt]

OP AMP / Comparator gui

An Operational Amplifier is wonderful thing. It has 2 inputs labled + and -. If the Voltage on plus is higher than the Voltage on minus the output pin goes high, vice versa and it goes low. With a bit of resistor jiggery pokery you can multiply or divide a voltage by anything you like.

If they make an Op amp and it turns out to be too clunky they mod the circuit to lose the drive high on the output and call it a comparator. You connect your input to one pin, a reference Voltage to the other and the output tells you which is the higher.

GUI usually stands for Graphical User Interface.

I can't comment on your circuit because I still don't know what is coming out of the Bob.