Hi, you know I really like the Hoo Fx8 solder n it's one of my favorites. I It's my recommended iron for beginners. Everyone keeps asking me which iron should you buy. Well re you can't go wrong with the FXAA.

It's really nice, but it's one annoying feature. Go home at night, turn the lights off and well did I turn my soldering iron off. Age old question. you get a bit paranoid and because the LED is normally off.

oh there it is, blinks on and it only comes on when you. uh, when it's actually heating the element which is kind of okay, but that doesn't uh when you, uh, that's no good when you glance over at the soldering IR as you live. Oh, did I turn it off or not? Yeah. I can have all remote switches and I'll probably eventually do that.

but anyway, it's just a bit of a design oversight. I Thought it' be much better if this thing actually had either a power lead or that Led there actually changed to green or something toggled between red and green. So it's always on because Murphy will get you every time you're walking out and you do a quick glance at it like that and like you're bound to miss it. it'll be off when it's the iron's actually on, it's no good.

So I thought I'd hack this thing and see if I can change the LED in it. Let's go and just looking at it. it is a very nice design tool. I Know some people don't like it, but I I just think it's It's quite artistic And it's designed really well.

The Nice: the nice lines on here and the compact footprint. and it's built like a brick dny it's really solid as with the big internal Transformer and they've really gone to a lot of effort to design it. In fact, here it is someone by the name of Toshiyuki K has designed it I guess he's an he or she is an industrial designer of note and they've signed it and they're quite proud of it and they love it and well I agree. a beautiful design, but it's lacking a bit of functionality.

Be much better if that Led actually didn't go completely off it just toggled between red and green. Bit of a design oversight. Oh well, you can't have everything but I think we can fix that. and to crack this thing open is pretty easy.

There's four rubber feet on here, you just have to peel them off and there'll be four Phillips screws under there. and I love that they have the adjustment tool in here. It's great for adjusting the cow pot on the front. It's just beautiful and you undo those four screws and Tada you pop it open.

There it is now I know I've done a tear down of this before, but I just can't help myself. Again, it's quite a nice design in here. And by the way, before you go poking around in here, just make sure you unplug the damn thing for safety. Okay, don't work on this thing with the cord plugged in cuz there's exposed Main's wiring down here.

They've got the switch down there and look, that's actually exposed wiring. but you know I've got no problems with that. It's in there nice and safe and sound. and there are really some nice design aspects to it.

It's uh, the primary up here is fused of course. and uh, it. the cable clamp down here. Excellent look at the solid look at how solid that cable clamp is.

It's just absolutely beautiful. And then they've put some extra um tubing over there as well and cable tied it down. They've cable tied them here. It's just nice.

They use proper uh mounting studs here for the Uh Earth Point mounting screws into the entire bracket. The Transformer looks like it's excellent quality. the you know the laminations and it'll just it'll. like last you 20 years like my Hoo 926 has.

or I think it might even be 25 years for the Heo 926. But ah, it's just a lovely design. And there's the 580 thyer down there mounted onto the aluminium base. like that.

They've gone to all the effort to bring it down there. They've heat Shrunk the uh, individual uh pins down here nicely and screwed it into the base for heat sinking. Wonderful! More cable ties here. Beautifully solded uh points on the Transformer I Love it! Now here's our main control board here.

It's a single-sided board. It's got a Heo branded chip on it, some surface mount uh Parts on the bottom side as we'll take a look at and uh, we'll have to get in there with some light and take a look at the LED and uh, see how that's mounted? First of all, what we're going to do is just undo this little grub. Screw in here and this knob just pops off like that. Beautiful! And this allows the board not to slide out all the way.

Unfortunately, because it looks like that, they, uh, sort of slide this board in as a first step and then they probably screw in the Transformer so it looks like you probably have to screw out the unscrew the Transformer to actually get enough room to, uh, get that board out, but you can actually rotate it um, like that and get it at least to there so we can actually access the LED down in there. It's just a standard 5 mm red LED with a PCB Mount spacer on the back of it which is really good and there's a whole bunch of room around it uh as well. So uh, we can get like a little board in there and put in a bit of uh, extra uh circuitry, hack in some circuitry to uh, make this lead turn red and green. So I Rather like that we can access it from the bottom of the board down here If we take a look at the PCB here, we can see the LED soldered at those two points there.

This track here looks like it's power on the top side going to ground and that's confirmed if you look at the polarity of the capacitor on the bottom. So this big uh flood track around here is ground and this one is power. so it looks like the LED is on the high side of the power rail there and it goes through and through R2 there which is a tiny little resistor and that goes through to one in on the chip so it looks like um, it's just an open collector uh driver on the output which just pulls that uh LED low. So um, we've got some easy uh capability there to uh do some alternate uh functionality to drive a red green LED and I've measured the lead dropper resistor and it is a 2.2k and the voltage rail is 9 Vols So what do we have inside here? Well, as I said, we've got an L to the high side of a 9vt rail through a 2k2 dropper resistor into an open collector.

Um, output driver on the IC it's a custom IC I'm not sure what device it is could be a microcontroller just branded uh hoo or something like that, but that's clearly what they're doing. so what can we do to add on a second? LED Well my first thought was when this output here goes low, we want, uh, we want this red lead to come on and another green lead to actually turn off. But when this open collector driver is Switched Off and the red lead is off, we want to switch the transistor on. So we want to switch another transistor on.

which so what do we do? Well, let's add another LED over here, shall we? Let's add a green LED I'm drawing it in red, but oh well. What the heck? Okay, and we've got another dropper resistor. Let's permanently tie that. Let's use two 2k2 again.

Okay, we're permanently tied that and that's our green thing. We'll tie that to the 9V rail up here so it's permanently on. but that's okay if you just want to do a Power LED but I don't want that I want the this lead to toggle I want it to be one of those by color leads. red, green that would toggle off or on because I don't want to drill another hole in the case and ruin the nice design and just put a power lid I want the one LED So how do we get this to switch between these two? LEDs Well Turns out it's pretty simple actually.

let's connect a resistor in here like this go through and what we want to do is short out this Led when it's off. So let's put in a Npn transistor there which connects across the green LED and let's just drive that straight in there. So when this goes low like this, then this transistor will switch on through here like this because the current uh, through the through the emid up like that goes through these two resistors down the ground and switches this transistor on and shorts out that Led. And yeah, there's some excess current flowing through the 2K to cuz you got 9 volts directly across the 2k2.

But who cares, right? So um, when your iron is dissipating, you know, 65 70 wat WTS doesn't matter a rat's ass now. Uh, when that. So when the red lead is on, this lead will be on, this transistor will be on, the green lead will be off and we want it to toggle the other way. So when this, uh, open collector switch opens and the red LED switches off because there's no current flowing through there like that anymore.

There's no current, so this, uh, will turn on this trans. sorry, it'll turn off this transistor because there's now no base current. uh, flowing through here at all because they're at the same potential like this. 9 Vols The base is effectively, um, at the same voltage like that.

So it's going to, uh, switch this transistor off and the green lid turns on. That's it. So it'll toggle between those two states. Beautiful now.

I Know what you might be thinking? You might be thinking that we can do away with this resistor cuz we already have a resistor here. Well, if you do that when uh, then the voltage drop across the Bassy M Junction here will actually swamp out this LED and switch the red lead off so you can't just do away with that resistor otherwise you'll find the red lead will never come on. but you could replace that with a mosfet uh for example and do it that way. you can get away with out the resistor.

But anyway. I Thought this was quite a neat solution and it would work. Unfortunately, it requires a red green bolor LED with a common anode. uh, common anode connection because there's the anode of the diode and they're connected together.

so it's a a thre Leed uh, a three Leed LED and it has one common terminal for both and then the cathode is a separate terminal for each lead. and it turns out common anode bolor LEDs rare as hen teeth so can I get one of those? All I can get is one of these um LEDs which is by color and they're back to back like that in the same uh in the same package. they're back to back. so going to have to scrap this circuit.

but I just thought I'd show you that anyway and let's try and figure out how we can drive one of these more readily available at least. Uh, what? I can get? Um here? anyway? uh, readily available backto back. LEDs Let's give it a go and just for a bit of what the heck fun I Actually built up that circuit we just saw and here's the red: LED Here's the green LED and this here simulates the this connection. This resistor here simulates the open collector output on that and as you can see, da da da There you go.

But you need a common either two LEDs like this or a common anode one. So exactly how do we drive one of these biral backto back? LEDs They're nasty. You got to switch them around. switch the polarity.

That's a not an easy thing to do in a circuit traditionally, but there is an easy way. One of the traditional methods is to just to use a logic inverter like this. You're familiar with with these. You get six in a package.

Digital Logic Inverter You just put the LED between the input and output VI a series dropper resistor there and bingo if you got one on the input, you'll have zero on the output. so one on here will forward bias this upper LED here and switch it on. And likewise, if you put a zero in here, you'll get a one out here and then that will forward bias this lower LED in here and it works both ways cuz you got this series dropper resistor in there so that's pretty easy, but we don't want want to use a logic gate for that? You get six in a package. It's pissing away five of them.

We don't want to do that. Want to be a bit more elegant, use like a transistor solution like we showed before. So I've sort of duplicated that circuit down here and you can think of these two Junctions as like the input and output of this inverter down here. And we've got two pullup resistors to our positive rail.

In the case of the H, it's 9 volts. And why have we added two pullup resistors there? Well, that allows us to drag either of these Junctions down to zero or even up on the high if you want. You can do things without shorting out the rail. So and they use them as lead droppers as well.

So let's take a look at how this works. Let's start out by taking the example of when the internal open collector drive inside the IC This is our existing Heo I down here. just like we saw before over here. Okay, and let's say this turns on and switches our traditional red our existing red LED on.

Well, let's look at what happens here if we pull this down to ground this transistor. The base is uh is cut off so there's no base current. so it switches this transistor off so you can just ignore that. that transistor there doesn't exist anymore.

It's switched off. So what happens? 9 volts flows through this resistor here. current flows through this upper LED here cuz it's forward biased down to ground. and bingo that LED lights up and you would make that the red one.

So we'll make this one down here the green one. or you can have any other color. You can use an RGB lead if you want. and ah, let's not go there.

Red Green. traditional. So Bingo when this works exactly the same as before. but let's look.

look what happens when it switches off the base current here and turns off this transistor. so this transistor here doesn't exist anymore. What have we got? Well, it's it's easy. What we've got here is this resistor up here goes through here.

and because this doesn't exist, current will flow through the base of this transistor and switch it on. pulling this Junction here down to ground. So not only will current flow through here like this and through the Uh base resistor down to ground like that, it'll also flow through the green LED down to ground. Bingo We've just switched on green LED and if you switch this off and on, it'll toggle and it'll switch between red and green.

Beautiful piece of cake. And once again, just like before, we can't emit this uh base resistor down here and just rely on this uh resistor up here to drive this base current. Well, the base current will be fine. It'll uh, this resistor up here will limit it.

this transistor will turn on fine, but then the base emitter Junction Remember that it's a diode. It's 0.7 volts drop. So this Junction here will be at the base of M voltage of 0.7 volts and 0.7 volts ain't enough to turn on a 2v LED Is it? No, Of course not. So if you admit this resistor, you'll find that uh, or short it out.

You'll find that the green LED won't switch on at all. Your circuit's still toggling, but green Led doesn't work. So if you're going to use a bipolar transistor like a 2 N22 or a 39 2N 3904 bc547 whatever, you're going to need that base resistor. But I Think we can reduce our component count? just one more and get rid of that resistor and change this puppy here to a mosfet.

So we'll do just that. We'll replace this with just a Bog standard Vn10 mosfet that can be any uh N channel uh, mosfet you like pretty much and uh, basically gate drain and S course it uh, works exactly like the transistor except that there's no none of that base emitter drop. So you can get rid of the resistor and just connect the gate directly to that Junction there. So Bingo! I Think this will work, We'll build it up, we'll give it a try and hopefully we'll be able to hack it into the He.

There should be enough room to do that. So uh We've basically got a three component solution. well, two if you count the existing uh existing resistor. but we probably won't use that.

but I think that's pretty elegant solution for a toggle red green indicator. There's other way, many other ways to do it I'm sure. but I just like this one. So we'll go with this.

Let's build it up and here's the circuit build up. but I'm using a bipolar transistor a 2N uh 3904 like I showed you in the first example and this jumper link here, uh shows you um, just simulates the uh hoo chip the open open collector output. so we'll toggle that and bingo it. Toggles between red and green.

Not a problem these um B this Led B directional LED I've got It's A J Car cheapy. It's not very good. I've had to lower these dropper resistors up here to one uh K But there you go. That's with a 1K uh base resistor.

and if we replace the base resistor there with a short that's actually a 1 ohm resistor there, then you'll find that the red one turns on, but the green one doesn't turn on as I explained. but it will do if we pull that out and we'll replace it with a Vn10 mosfet. Got to get the pins correct here assuming I've got it in the right way. I think I do and let's disconnect that Bingo There we go: Red, green, red, green.

isn't that terribly exciting I think we've got a nice solution there. All we need to do is build that into our hoo. and of course, just make sure you've got the Led the right way around that you want it before you actually proceed with this cuz it would uh, suck to have wire the LED in backwards. It would still work of course, but uh, you'd have your red green back to front.

can't have that. So here's my completed assembly and uh, as you can see, it's not uh that complicated at all. just uh, follow the schematic. the LEDs like that the resistors e um one one resistor on each pin going into a common point which goes to a I've got this going to a red wire which will go to the plus uh 9V connection.

The brown wire down here is um, the Uh Source pin on the Uh transistor and the orange pin. Here is the gate and that will go to the Um switch position on the Led, the existing um uh LED common common collector switch position. So there you go. that's the entire assembly.

It should be in right angles like that. go up against the front panel like that and then all this stuff will go down the base of the board. The board will be about here about this distance from it so it shouldn't touch the board. not that there's anything to touch cuz there's no tracks on the top side so that should, um, fit in there quite well.

Let's wire it in and here's our connections on the board here. We've got uh, ground over here on this side of the cap and we've got the red wire which is the plus 9 volts coming from the other side of the cap and then the orange wire is the uh gate wire and that goes directly to the bottom side of the resistor down here. And once again, don't poke around inside this thing unless you've got it switched off. Safety First All right, let's power it on and give it a try.

and once again, make sure if you're going to do this, make sure you don't short the board the uh board out to the Transformer at all. Make sure it is back cuz it can move. Let's do it and it's red and it's green. There we go Bingo Woohoo! Now that is weird.

It's not working as I expected I Expected it to uh, come on and Flash uh red for a little bit just like it did for a longer period like it did when we just had the regular LED in there in the normal product, but it's not. There's a little flash, you see the little flicker of red there and if I actually um, heat up the iron I mean uh, sorry if I cool it down, it's sort of. That flicker rate kind of increases a bit, but there's something weird going on there. I I Don't think this is actually a just a, um, a straight, uh, logic low output.

Maybe they're Pwm in it or something and that's causing some weirdness to happen I think it's time to get the scope out. Okay, what I'm doing here is I'm probing the output uh, from the chip uh itself. uh, directly on the pin there, which we thought, which we know is open collector, um, output. but I think we might be getting, uh, some sort of Pwm signal on there.

So once again, uh, Safety First with this thing, when you probe it around in here, it's safe because we've got an isolated Transformer so it's electrically, uh, safe as far as that's concerned, but you can easily brush the main stuff on top of there not insulated. I Recommend if you're going to be probing around, insulate all this stuff, or just hand completely. Hands off. Can't stress that enough.

So let's turn it on and let's capture the signal. T Oh, we've caught something. Let's try it again. Aha, there you go.

Pwm. There you go. There we go. And that's why it's yeah, that's why we're getting some flicker like that.

So what I've done here is I've added a 220 mic uh cap uh 16 Vols or greater uh to the across the open collector output of the chip or from the gate um of the mosfet to ground and uh, that might keep the uh red lead on a bit longer. Perhaps you know you can experiment with these values I've changed the Uh lead drop resistor down to 1K which uh of course makes a difference with the Uh time constant. Makes it worse actually, but as you can see, it is flickering and if I cool the sponge down a bit then it does actually go red like that, so that's that's nice. I'm pretty happy with that solution.

I think I'll uh, pack that in there and uh, be done with it and no hack is complete without hot snot. So that's what I'm going to hold the LED in there for. Fortunately, the nozzle's a bit small to actually get quite right in there, but ah, that won't stop me. There you go, and that'll be good enough for Australia I Love it! So the board just slides back in there like that and the um, uh, the mod in there doesn't touch the board at all and we've got our LED in place.

Beautiful and it's all back together. Let's switch it on. Tada it's red and it will eventually go green. and now I don't have to worry about leaving my hoo on beautiful and if we turn the wick up a bit, bang it instantly.

uh, switches on the heater and it will eventually come good. And it's pretty obviously what they're doing with the lead there. It's got no fancy pulse stretcher or uh, anything like that on. they just, uh, probably just taking the output for the Led directly from the Uh switches.

So there's our final circuit we used. Uh, if you want, if you've got a bright, uh, efficient LED you can use 2 K2s up here. as originally I used end up using 1K 100 mik or a 220 mic or something like that. got to be at least 16 Vols because your rail's at least 9 volts and Bobs your uncle Works a treat.

There's some room for improvement here if you want to get um, if you know you could add a micro or something fancy to get the LED to Blink and do all sorts of weird and wonderful things if you're that. Keen but nah, I like the single transistor solution. catch you next time.