Help with Bulgin Switches, flip flops, transistors and opto isolators.

[Mysterae]

This is part of my case mod parallel HEX over in the worklogs forum. I thought I would post this here as it's still in the research stage and didn't want to clutter it with my ageing electronics knowledge! I'll post the result from this thread over to the worklog when the circuit has been built and finished.

I know this all might sound crazy, but bear with me!

The idea is to have Bulgin momentary led switches turn on an off a laser, the leds of the Bulgin switches and the leds of my fan controller. Switch 1 will control the laser and Switch 2 will control the Bulgin switch leds and the leds of the fan controller.

Starting from cpemma's design and the info gleaned from his very helpful website, I have the basic flip flop circuit to start with. I have kept the same format of drawings as cpemma throughout.

LASER CIRCUIT
Dealing with the laser circuit first of all, the laser requires 9V to run but the power requirement is unknown at the moment, but shouldn’t exceed 1A. To add to the design, I only want the laser to come on when the led at the back of the Tagan PSU is lit. This blue led comes on when the psu load exceeds 20A. The voltage powering the blue led is between 5v to 12v, I can’t measure this at the moment as my system is apart!

Ideally the circuit I build should be electrically isolated from the PSU led, and I have thought about 2 ways to do that. The first is using a phototransistor taped face to face with the psu led, so when the psu led lights, it activates the phototransistor.

Using a phototransistor:

For the laser to be on, S1 is pressed activating the 4013 output to high, giving voltage to the SFH300 phototransistor. When the phototransistor receives light from the psu led the TIP122 transistor is activated and the laser will be powered. That’s how I think it should work.

Things I’m not sure of:
1. The need for the 3v zener diode before the lasers supply because of no.2 below.
2. The drop in supply voltage because of the TIP122 transistor (typically 2v).
3. The placement of the R4 resistor.

The second method I thought about was using an opto isolator.

Using an opto isolator:

The actual led of the psu is removed and the wires that supplied it connected to the anode and cathode of the opto isolator. A suitable resistor may have to be fitted in series as the opto’s internal led has different characteristics from the psu’s blue led.

When the 4013’s output is high and the opto’s led is activated by the psu, transistor Q1 is activated allowing the laser to turn on.

More things I’m not sure of:
1. The placement of R4 resistor again.
2. The voltage output at the emitter of the opto isolator is sufficient enough to activate Q1
3. The volt drop at Q1 and the need for the zener diode before the laser.


STEALTH MODE
The next circuit as mentioned before will control the Bulgin switch LEDs and the leds of the fan controller.

The leds of the Bulgin switches require a resistor and have different characteristics depending on their colour. I have 4 switches in the flowing colours:
Red – Forward Voltage – 1.85V
Green – Forward Voltage – 3.5V
Amber – Forward Voltage – 2.3V
Blue – Forward Voltage – 3.5V
(All rated at 20mA)

The fan controller is a 4 fan PWM type, and each fan circuit has 3 leds – blue, green and red (low, med, high). The idea here is to remove the leds from the controller, mount them remotely, but switch them through a quad opto isolator, a TLP523-4. Since the fan controller has 4 fans x 3 leds each, I need 3 quad opto isolators.

The circuit above uses the other flip flop of the 4013 from the laser circuit. When Q1 (of this circuit) is activated from the flip flop, the Bulgin switch leds will light and internal leds of the opto isolators will activate. This will allow the leds of the fan controller to light as required.

Once the correct circuits above are sorted, the laser circuit and stealth circuit will be combined into one.

All help with selecting the best circuit, better components or corrections is appreciated!

Useful datasheets (some links are pdf's):
Bulgin LED Switches
Phototransistor SFH300-2
Transistor TIP122
Flip Flop 4013
Opto isolator TLP523-2 and TLP523-4, and a list.

 

[RancidWAnnaRIot]

I"m sure i could help.. but i'm way to busy right (gotta study for a final... gotta stop wasting time on hardforum too lol) now lol... looks interesting though

 

[Mysterae]

Rancid, what's more important? Good luck with your final!

 

[Mohonri]

Ok, let's see if I can answer some of your questions:
For the laser circuit--If you can, see if you can find out how much current the laser draws. In any case, I'd suggest adding a resistor (assuming 1A draw, and a Vc-e voltage on the TIP122 at 2V, it would be 1Ohm in order to leave 9V for the laser) between the emitter and ground. The datasheet shows the voltage across the output of the optoisolator to be just over 1V, so the emitter voltage will be 4V. You have 2.5V drop from base to emitter on the TIP122, and you'll want 1V from emitter to ground from there, so you'll need a base voltage of 3.5V on the TIP122. That means R4 will have to drop 500mV @ approx 1mA, so R4 will be around 500 Ohms. You might consider using a 1k pot to adjust the circuit to get the brightness you want. This configuration will also let you eliminate the zener.

Personally, I'd opt for the optoisolator in lieu of the phototransistor--it's a bit more elegant. You could power the LED off the TIP122 if you still want it.

As far as emitter output is concerned, you've got plenty. The 4340 has a capacity of 130mA, and the Tip122 has a current gain of about 1000, so you've got plenty of leeway.

For stealth mode, is the flipflop switching all the fan controller lights from off to fan-controller-controlled? I see nothing wrong with the circuit, although optoisolatos do seem like some sort of overkill...

One more note: You can safely eliminate C3 and R6. They're there to make sure you have (somewhat) steady power and to make sure the circuit discharges when it's disconnected from power, but both of those needs are already satisfied by the rest of the computer/PSU.

EDIT: Oh, one more thought. You could just use a jk flip-flop--it can do the switching for you, instead of having to feed the output back around to the input. The pin-out is similar--just hook j and k to positive voltage and let'er rip.

 

[Mysterae]

Mohonri, thank you for your help!

I'll be getting the laser tomorrow back of the person who borrowed it, so will no know the current required for it. When you say

suggest adding a resistor (assuming 1A draw, and a Vc-e voltage on the TIP122 at 2V, it would be 1Ohm in order to leave 9V for the laser) between the emitter and ground

you mean the emitter and ground of the optoisolator or the TIP122? I'm also not sure why the emitter voltage of the optoisolator would be 4V.

I agree that an optoisolator is better than the fudge method of a phototransistor!

As far as emitter output is concerned, you've got plenty. The 4340 has a capacity of 130mA, and the Tip122 has a current gain of about 1000, so you've got plenty of leeway.

Not sure what you mean by 4340, you mean the 4013 or TLP523, or are you making a suggestion ?

In the Stealth Mode circuit, the flip flops are mearly closing the circuit of the leds of the fan controller. The fan controller is a completely separate circuit and having looked at the board I can't see any reasonable way of breaking into it except what I come up with.

Regarding C3 and R6, they were included as they were in cpemma's original circuit. If the only reason for them is to steady the power and will not alter the circuit 'on' state, I'll remove them, thanks.

I'm not sure why cpemma didn't suggest a jk flip flop, perhaps it was the supply voltage? I'll be getting some components and bread board and have a play soon!

Thanks again for your help.

 

[RadRob]

I noticed in the fan controller that all the quad-optoisolator LEDs are run in series through Q1. I don't believe the 12V is going to be enough to light all 12 opto LEDs. From the data sheet the typical forward voltage drop is 1.15V * 12 requires 13.8V just to light LEDs plus you will have some drop across Q1. As an alternative I would route the quad-opto LEDs in parallel with dropping resistor for each.

I just thought I'd bring it to your attention.

 

[Mohonri]

When you say

suggest adding a resistor (assuming 1A draw, and a Vc-e voltage on the TIP122 at 2V, it would be 1Ohm in order to leave 9V for the laser) between the emitter and ground

you mean the emitter and ground of the optoisolator or the TIP122? I'm also not sure why the emitter voltage of the optoisolator would be 4V.

Yes, I mean the emitter and ground of the TIP122. The reason for the 4V on the emitter of the optoisolator is because you'll drop about 1V across the optoisolator and I was assuming a 5V signal coming from the 4013.

Not sure what you mean by 4340, you mean the 4013 or TLP523, or are you making a suggestion ?

Whoops. I meant the optoisolator has a 130mA capacity. (the datasheet was 4340.pdf, so I got mixed up)

In the Stealth Mode circuit, the flip flops are mearly closing the circuit of the leds of the fan controller. The fan controller is a completely separate circuit and having looked at the board I can't see any reasonable way of breaking into it except what I come up with.

I think I understand a bit better now--you're using them pretty much as solid-state relays. That ought to work fine, although it's not the most elegant design, and the voltage drop across the output side of the optoisolators might affect the brightness of the fan controller LEDs. If that happens you might end up having to do some more tinkering. Using them as-is certainly won't be dangerous or bad--the worst thing that could happen is your LEDs don't light up as bright (or at all!).

There's another way of doing the same thing with AND/OR/NAND/NOR/XOR gates, but the benefits would be insubstantial at best.

 

[Mysterae]

I noticed in the fan controller that all the quad-optoisolator LEDs are run in series through Q1. I don't believe the 12V is going to be enough to light all 12 opto LEDs. From the data sheet the typical forward voltage drop is 1.15V * 12 requires 13.8V just to light LEDs plus you will have some drop across Q1. As an alternative I would route the quad-opto LEDs in parallel with dropping resistor for each.

I just thought I'd bring it to your attention.

Thanks, I had *partly* thought of that. If you look closely at the circuit you'll see there are two parallel circuits with 6 leds of the quad optoisolators each branch with 270R resistors (R9 and R10). What you have brought to my attention is the volt drop at Q1, I reckon being 2V, means the opto's circuit resistors will need lowering to perhaps 180R. Thanks for the reminder!

Mohonri, I thought the output of the 4013 would be 11V, subtracting the drop as I'm supplying 12V source. I'll have to check that, and will affect the voltage of the input to opto and TIP122 of the circuits.

I think I understand a bit better now--you're using them pretty much as solid-state relays. That ought to work fine, although it's not the most elegant design, and the voltage drop across the output side of the optoisolators might affect the brightness of the fan controller LEDs. If that happens you might end up having to do some more tinkering. Using them as-is certainly won't be dangerous or bad--the worst thing that could happen is your LEDs don't light up as bright (or at all!).

There's another way of doing the same thing with AND/OR/NAND/NOR/XOR gates, but the benefits would be insubstantial at best.

That's exactly how I'm using them, as solid state relays. Having them less bright than what they are is no bad thing I want to keep the circuits isolated for noise, safety and to revert back easy if I decide to remove it for any reason.

 

[Mohonri]

Thanks, I had *partly* thought of that. If you look closely at the circuit you'll see there are two parallel circuits with 6 leds of the quad optoisolators each branch with 270R resistors (R9 and R10). What you have brought to my attention is the volt drop at Q1, I reckon being 2V, means the opto's circuit resistors will need lowering to perhaps 180R. Thanks for the reminder!

Not to mention that since these are optoisolators, you don't have to care about any voltage difference between the LED and detector halves of the circuit. The fact that the LED side of the isolators gradually decreases in voltage doesn't mean that the outputs of the optoisolators will be any different from each other. That's a cool side effect that I hadn't considered.

Mohonri, I thought the output of the 4013 would be 11V, subtracting the drop as I'm supplying 12V source. I'll have to check that, and will affect the voltage of the input to opto and TIP122 of the circuits.

Yeah, you'll have to double-check your datasheets for that. I imagine you're right--the output will probably indeed swing 0-12V (or something close to that). I'm just used to using 5V circuits.....

 

[Mysterae]

With a few minor tweeks and few component changes, it works!

The circuit diagram below is the laser part of the circuit. I changed to a 3V laser and a different single low current optoisolator (SFH618A). The 2 AA batteries are simulating the signal that I will get from the psu when the current exceeds 20A, everything else is running from a 12V supply.

The lower part of the breadboard circuit has the quad optoisolator which I changed to a ILQ74. The four (really too bright) blue leds are simulating the state of the fan controller leds once I get round to wiring them in.

A few resistors are at their wattage limit (0.25W) and are getting hot so I will have to change a few of them too. All I need to do now is to get this on some strip board or etch a pcb for it, not decided on that yet.