Hi welcome to the Eev blog an Electronics Engineering Video blog of interest to anyone involved in electronics design. I'm your host Dave Jones Hi. As you may know, I've been involved a little bit in the Triple 5 design contest that uh Chris Gaml and Jerry Ellsworth put together because I'm judging the Australian uh aspect. there's an Australian prize which I'm giving and I'm going to be judging that.

so I couldn't really enter the contest I'm too close to it so um I tweeted some time back that I was actually going to do my own triple 5 um timer circuit just for fun. You know, enter it at make a good blog anyway. I thought so yeah. I go ahead with it I was playing around with the damn thing and it it was just playing up on me I found this weird Quirk and I It took me ages to track the damn thing down and I've finally done it.

and let me show you what I found. It's really interesting as you may know, the triple 5 timer was designed by a guy called Hand Kem's in and he's famous for it as well as other stuff as well. and he's actually judging the Triple 5 design contest which is totally cool, but he's always publicly said that the that the number triple 5555, not this Triple Nickel rubbish has, um, was just an arbitarily assigned number. but if you look at the internal circuit and I just so happen to have it here on my t-shirt there are famously five resistors in there.

in the standard uh version, it isn't the same in the Seos version, but anyway, there's uh, 5K, 5K and 5K and it's publicly claimed it's not. You know it's just a Rand randomly assigned number, but everyone in the business knows that's complete now. Um, there's also been I Heard a rumor like decades ago that he added something else in the chip as well as a little Mark for the Triple 5, but nobody's ever found it and you know he's denied that as well. But I I Not sure.

I'm not going to claim it, but possibly I might have found something and he needs to explain it. Let's let's have a look at it. Now here's the circuit I built up on breadboard. It actually took me some time to actually, uh, do this I'll show you up close in a minute.

but um, uh, here's the Dave CAD drawing of what I've actually got here on the breadboard. I'm going show you up close. um, but it's you'll recognize it. it's a standard as stable Tri 5 Timer circuit um, you know, know pins 8 and four up there Wonderground and it's just a standard configuration, but I've added in an adjustable uh pot up here so I can adjust the frequency and I've tweaked this value with a couple of parallel res series and parallel resistors in there just to tweak it to get to the exact frequency.

which you'll find out actually matters. And one of the key things is I haven't got a capacitor going to ground on pin five? Uh, now that is a recommended configuration. They recommend like a 10 naner capacitor to on pin 5 to ground, but my circuit that I was playing around with didn't have that and I realized that you that is the key. One of the keys to this.

There are two keys to this which you'll uh, find out and I've just added a low pass filter to the output so that I can see some stuff as you'll see later. But let's check out the circuit on the board and here it is wired up exactly as per that Dave CAD uh drawing. Here's my adjustable pot up here which I'll use to adjust the oscillator frequency. that's my low pass filter there and I've got a bypass cap on there.

but as you will see that, uh won't have any impact on this now. let's uh, take a look at the problem and see what we get. Uh, as you can see, I'm probing the output here. this is the PIN 3 output and I'm also probing the output of the low pass filter here and you'll note that there's no bypass cap on pin five and as you'll see later, that's pretty key to this.

uh, whole thing. Or it's one of the keys. There's a couple of keys to this, but uh, let's see and I'm measuring the output now and as you can see, it's um, about 55.2 khz. Okay, just over 55 khz now.

I'll see if I can get all this in the shot here. Sorry, it's hard um to get the frequency and pot and everything, but let's see if we can recreate the problem I've been having I've got my adjustment pot here and let's wind up the wick on this thing. let's is that in shot? Yep. okay, okay, let's wind up the wick on this and see.

watch the frequency over here once it gets to 55.5 Hertz you'll see something rather remarkable. I've got some average in turned on here just to stabilize it because the triple 5 is not uh, the most, uh, stable beast. and as you it's starting to get a bit wobbly now as you can see it once it hits 555. Bingo look at that that it's jumping around and if we go past that, if we go past it, okay, we're we're out.

So let's go back down to that Wa there we go there. What there have we got it? Have we got it? I think we've got it all right and look, it's modulating. it's something. Look, it's it's wobbling all over the place.

That's because of the average in. So if you turn the average in off, okay, let's turn the average in off and look at look at this thing. Okay, look look, there's modulation on there at 55.5 khz 555. You know what can you say I don't know.

We I need to investigate this a bit more. but let's actually do this. What I've got is the low pass filter up here? Okay, so let's um, we have to go. Uh, trigger off.

uh Channel two here. So let's trigger off our second Channel up the top and look at that. look. look at what we've got.

that that filter that low past filter down in the circuit down here is just taking out, effectively taking out the 55.5 khz uh carrier. uh, frequency as you know to want of a better term and it's um, it. Look at the output here and that's on frequency 2. Look, it is 55 I'm not kidding you, it is 55.5 Hertz Modulation We can turn the average in up a bit more here.

Let's oh sorry that that that is no averaging. Let's turn the averaging on okay and you'll see that the other Wh sorry. you'll see that the other waveform disappears. of course because we're now averaging and check it out.

Look the frequency of that channel. the modulation is 55.5 Hertz at uh um at 55.5 Damn. KZ in this circuit, What the hell is going on? It's nuts. Okay, so what I'm going to do now is I've got a 10 Narad um cap and I'm going to put that as per the application.

Noes on Uh, pin five of the Chip and see our mod we we. We're still modulating here. Look, it's still I haven't I haven't adjusted that pot any further. So let's let's whack this on here at um, where is it? Oh, hang on, hang on.

I'm going to have to go pin five and check it out. Look, there is no more modulation. It's it's nuts, What's going on And right if you, well, that's put the application not, it's probably not. You know, cuz that's how you're supposed to use the device.

and that's why probably no one has ever found this thing. But look, if you, if you physically remove that cap, look the the modulation. Just it. It comes back.

it's nuts. Now if you're thinking like I was that, maybe it's got something to do with my external 5V external bench Supply I'm using here. But um, and maybe it's some weird, uh, decoupling effect because the frequency of the triple 5 um can actually be. Well, you know it can be sensitive to your power, very sensitive to your power supply rails.

but let me. so I Thought like it was the decoupling cap. but let's physically remove the decoupling cap off here. Whoa.

And it still doesn't I mean there's the extra ringing, right? Because there's no decoupling on there, but the modulation still remains. It's still doing exactly the same thing. and if we uh and if we change that, if we go trigger off uh Channel 2 again, and if we boop boop boop we've still got that 55.5 HZ modulation. It's crazy.

Even with the decoupling cap gone. yeah, I know what you're thinking? That wasn't good enough for me either. So what I've done is I've um, uh, powering it now from a battery pack I've completely disabled these uh inputs in my external uh Supply and um, look it it. it's exactly the same.

Exactly the same modulation and I it's just nuts If we go in and we trigger off Channel Two again and we sweep it down and there it is. it is still 55.5 HZ modulation when you hit 5 5 uh5 KZ And of course, with that uh battery circuit because the battery will actually change the um, the battery would actually physically change the frequency. uh, because it is. It's not spot on.

Five: it's about 5.3 I've got a couple of alkalines and some rechargeables in there. It's about 5.3 So I had to retweet the pot, but that's all I had to do to get it to do exactly the same thing as what we had before now. I Want to know how the bloody hell it's doing that? When there's just you know it, it's the um, there's it's just a standard as as stable triple 5 timer circuit with uh without the control um modulation capacitor on uh pin five to actually um, stop any uh modulation or oscillation or stuff like that and you still get the 55 Hertz output. You whack that cap on and it just vanishes.

That's per the application note. but yeah, sure, I was trying to use the thing outside of its application note specification. but I Found something really, really interesting here. and in case you're wondering what, uh chip I'm actually using it is a National Semiconductor.

uh chip? sorry, it's hard to. It's hard to really get chips. you got to get the light right. But I've actually tried um, a TI brand chip and it's exactly the same.

It's exactly the same thing, so it's not just, uh, the national, Uh Instruments device it it seems to be. well, it's at least across two. Brands So if other people can try out other brands and see if it does exactly the same thing, we'll see if this is across the board on all triple. F So there you go.

That's the most bizarre thing I've ever seen. I Came across this when I was prototyping my little Vera board. uh circuit I was getting all sorts of little funny things cuz I was trying to do something weird with it for the contest. so I wasn't using using the Um I didn't have the standard bypass cap uh to ground on the control pin and I was getting and it took me ages to narrow this damn thing down to 55.5 KZ And then the damn thing modulates and I've tried two different devices from different manufacturers.

It does exactly the same thing. It only happens at 55.5 KZ And It only happens if you have the Uh control pin uh, not connected at all and you get the 55.5 Hertz modulation. It can't be a coincidence. Surely this is triple Five timer.

It's famously got the 555 resistor in it at 55 khz. 55.5 Herz Modulation: It can't be so. I've got to uh, get in contact with Hanss and find out uh, what's going on here because well I don't know but something smells fishy. So I don't have the Seos to try out Um or other brands.

These are the two I had in stock here. so build it up and let us know. Take a video, let us know if you can actually get confirm this the same thing is happening. Catch you later.