Switch Design

[savage]

Hi,

I'm working on a sort of switch, with the following characteristics:
- Iluminated OFF message on the Switch if Off (2 x RED LEDS)
- Iluminated ON message on the Switch if On (2 x WHITE LEDS)
- Back Lighting (4 x BLUE LEDS)
- Ability to switch off Back Lighting (Microprocessor)
- Ability to switch off Ilumination when ON (Microprocessor)

Now, for some reason, my SPICE model started to give me errors (Hate the dreaded software), but the circuit is attached. Can anyone tell me if this will work? Some suggestions perhaps?

I use 2 x 7805's because of the load. I will more than likely replace L1-4 with Ultra Bright LEDs, and the Back Lighting (L5-8) will also almost surely be more than 4 LEDs - and they are Blue

What I'm not to sure about... Will the 7805's cope with this? If I receive a -5V (from my Microprocessor) at BlackLightsM or BackLightsH, I effectively create a Short on the circuits. Best case scenario I think, I will just end up with a couple of 7805's that gets rather hot. But I don't want to have toasted components either :shock:

Any ways... Can Moses and the other extremely bright people on here perhaps just have a look, and come with some wise words of wisdom for me?

-5V on BlackLightsM Shorts L3 & L4 (Thus, they won't Illuminate when SW1 is ON)
-5V on BackLightsH Shorts L5 - L8, thus no Backlights on the switch
I return either +5V, or -5V back to my Microprocessor to indicate the ON/OFF position of the switch
- 1N4004 is to prevent feedback,
- R1 to cut off some feedback. According to my Splice, I get a weird 1.8V feedback from SW1, regardless of the position. Yes, 10K is overkill, I think I ended up with a value like 120Ohm which is not yet updated on the diagram.



Thanks,
Chris

 

[Nigel Goodwin]

The entire circuit doesn't make much sense, for a start there are no series resistors for the LED's, so they would be instantly destroyed. Also, you have the blue LED's in parallel - this isn't a good idea, you should have individual current limiting resistors to each LED.

You also don't appear to have any kind of switching shown in the circuit?, if the switching lines are going to a micro-controller you would fry it!. Use switching transistors to switch the ground side of the LED's, fed from the micro-controller - check the Hardware Extras section of my tutorials for examples.

There seems no reason to use two 7805's?, the current to the LED's should be limited to FAR less than 1A.

 

[savage]

Hi Nigel,

I asked for wisdom, and I received it

The switching itself, is handled by SW1. Taken your advice now, came up with the below... Let's see if it's any better now.

- 1 Regulator, +5V for everything is enough yes
- Backlights is handled by D1-D3. And Q1 is triggered by a +5V Signal coming from my Controller
- 'OFF' Indicator Lights, D5-D6. If SW1 is off, these light up
- 'ON' Indicator Lights, D7, D8. If I have a +5V on Q2 (Coming from my controller), the lights light up, indicating that the switch is 'OFF'
- If SW1 is 'ON', I take +5V and send it back to my controller.

Is this better? Makes sense?


Thanks,
Chris.

 

[Nigel Goodwin]

Yes, that looks better!.

You may be able to run the LED's in series pairs (having a single resistor for each pair), depending on the voltage drop of your LED's. Blue ones have the highest drop, but the others should be OK.

 

[audioguru]

Hi Chris,
Your circuit looks much better now, but:
1) What is the regulator for? A heater?
2) Why is the LED current so low and half as much for the blue LEDs as for the others?
3) Where can you get 450 ohm resistors?

You can save some of the current-limiting resistors for the LEDs if you put some of the LEDs in series, in series with a single current-limiting resistor.

 

[savage]

Ellos,

1) The incoming volts arn't 'guaranteed'. Basically, this is a small part of a larger project. There may be times that the incoming voltage will be either to low or too high (Most likely to high). Just this single switch alone, will feature arround 60 odd times. Thus, I use the regulator to ensure that I do not use to much voltage, and possibly blow the circuit (Or other parts of the project). Still intend to put some regulators and/or Bandgap Voltage References on the other inputs as well. Basically, it's for protection. If a 5V Regulator is going to get hot from a 9V Input, then yes, I definately need to look at it...

2) Hmmm... Changed R9/10 to 1K, the current limiting resistors to 220, and Q1/2 are 2N2222 now. Seems a bit better. Appart from moving the LEDs into Series, anything else I can possibly look at here? You are definately right though, it's way to weak... These LEDs need to *really* light up (but not burn out!!!). Perhaps also 12V Regulated with the LEDs in series... I'll have to play

3) See above?

Thanks as always, looking forward to the ideas...


Chris.

 

[mstechca]

It looks like in your circuit, you are depending completely on the input to turn BC108 (at the bottom) on.

and, how are you going to make on and off sign with under 10 LED's?

and the closest resistors to the ones in your diagram is 470 ohms.
Just don't go under 330 ohms, unless you know ohms law, and you are using a low enough voltage.

 

[savage]

Circuit changed considerably... Uhm, It did change. I no longer depend on the input to determine the position of the switch. The output merely indicates the status of the switch - which will be fine, and far less complicated / work (Even has a small fade effect in now).

I'm not making on/off SIGNS... Hehe, It's merely a indicator to show the position of the switch. The button that goes over the switch has two transparent sections. Thus, if the switch is on, the button iluminates (say, yellow). If the switch is off, the button switches and iluminates in, say red.

--
Chris