TSP #3 - Camera Flash Circuit and Nixie Tube Tutorial (Part 3/3)

In this episode (Part 3/3) Shahriar explores the principle operation of a camera flash circuit. The flash circuit is analyzed at the schematic level and through measurements. He then moves on to power a nixie tube using this circuit and calculates the efficiency of the DC-DC converter for this type of application. There is also a little quiz in this episode! Whoever solves the quiz will chose the topic of the next video.

>> Here we go. I'm going to use the edge of this.

I'm already wearing protective glasses because this will cause a big spark.

Please don't try this at home.

There we go. I'm going to connect it to terminals together.

Ready? Here we go.

I had my eyes closed. So I hope you guys saw that.

That was the entire charge

in a capacitor going through the short-circuit tip of this.

You can see it actually damaged the tip of my X-Acto knife here.

They wouldn't focus on this very well.

But now you can see that a voltage across

the capacitor went down all the way to 11 minus seven volts.

So, let's now do the same thing, but this time,

let's take this to the oscilloscope and connect the probe on

the voltage that I was telling you about, and

the node I was telling you about I'm interested in seeing.

I'm interested in looking at this voltage right here

and seeing the oscillation I was telling you about. So, let's take a look at that.

Okay. Here we are at the oscilloscope.

I'm going to be using my older scope for

this because I'm going to be putting a very large voltage,

and then I don't want to risk damaging my new digital scope.

You can buy one of these older CRT-based scope from eBay for about $200.

They're very useful. I highly recommend it.

So, here's the flash circuit.

It's already powered up using my power supply on the left.

I'm not running this at its full capacity.

I'm running it only from 0.6 volts because I don't want to create a very large voltage.

I just want to demonstrate the principle of operation.

So, what I'm going to do is I'm going to use the oscilloscope probe

and look at the voltage right before and after the diode.

So, let me see if I can get this to focus.

There we go, almost.

Right. So, here you can see the diode right there,

and I'm going to look at the voltage before and after the diode so we

can see the peak detection and also the large voltage swing I was telling you about.

So, what I'm going to do is I'm going to connect

the negative terminal of

my 10 to one probe and it's important that this is a 10 to one probe.

So, I will connect that to the negative voltage of the power supply.

I will take this cap off,

and then we will focus,

zoom in a little bit more on the display.

So, you can see the display of the scope is set to 50 volts per division,

meaning each of these vertical lines and vertical divisions is 50 volts.

So, there's eight of them in total, one,

two, three, four, five, six, seven, eight.

So 400 volts, a peak-to-peak signal can fit in this display.

Right now, the middle line is the ground.

So the signal in the middle is zero volts.

So, I will connect it right where I was saying right before the diode,

but I'm going to have to do that from the opposite side of

the PCB because I cannot really reach that.

I flip it over.

This is after the diode,

and this is before the diode.

I'll put this on the ground and then I will connect it.

Here we go, like that.

So, you can see there is an excess of 400 volts peak-to-peak of swing there.

The negative swing is clipped at the bottom.

You can see the bottom part is clipped.

The reason is because that's where the diode starts conducting and,

therefore, the capacitor starts to charge.

So, that voltage does not go below there because

the capacitor is so big that clips a voltage at the bottom.

But you can see that right now,

the voltage across the capacitor,

you can tell by where the clipping happens must be around minus 200, minus 250 volts.

If I connect this right to the capacitor,

you can see that it goes below the vertical division,

below the lowest point here is because it's less than minus 200 volts.

So, there's one other thing we can get from this.

If I connect it, we can measure the frequency of oscillation.

Each horizontal division is 50 microseconds.

So, if I connect it,

we can see that the cycle repeats once every 100 microsecond.

That's equal to 10 kilohertz.

Ten kilohertz is audible because you can hear 10 kilohertz.

In fact, you must have realized whenever you turn one of these things on,

then it makes that really annoying high-frequency pitch.

The reason that happens is because the frequency

of oscillation is within the audible range,

and the coil is in the transformer vibrate ever so

slightly because of so much cranes in them in the magnetic field.

Shift them left and right very little just enough so that you can hear.

So, the whole circuit emits sound when it's operating.

That's another reason why it makes that noise.

So, what I'm going to do now is that now we

have spoken a lot about how this circuit works,

looked at some other voltage or the oscillation and

a whole bunch of other characteristics,

what I'm going to do now, is I'm going to connect this to

a Nixie tube and then see if we can power a Nixie tube with one of these things.

So, let's move back to the other side and let's try to do that.

So here, I have a Nixie tube.

This Nixie tube shows numbers between zero to nine and it has also two decimal points.

So, the way these Nixie tubes work is that the gas inside

this tube is low pressure neon sometimes mixed with mercury and argon.

You have around on the outside,

you may be able to see it,

there's this mesh that's connected all the way around,

and at the back is a solid plating that's connected to one of these pens.

That's the anode pen.

What ends up happening is by putting a large potential difference

between this mesh on the outside and

the little numbers in the inside that you may be able to see,

you're going to excite the neon gas that's in there,

and the neon gas is going to glow.

The exact principle of operation of how it

happens and the physics that goes into it is an interesting read.

I suggest that you take a look at it,

but the principle of operation is what I said.

The gas gets excited,

the electrons move to higher energy bands.

On their way back down,

they emit light in the frequency and the wavelength that we are able to see.

That happens near the cathode elements of this Nixie tube.

Why does it happen near the cathode element?

Now, it is a little bit of physics that goes in there too.

I recommended you, take a look at it.

But in order to turn one of these things on,

you need to apply somewhere between 150,

160 of volts between the anode and the cathode of this particular model,

and then you'd be able to turn those numbers on.

These guys were invented and used back in the '40s and

the '50s when seven-segment displays,

an LCD displays and vacuum fluorescent displays weren't available yet,

and you could show numbers with these.

So, if you ever had an old HB or a very old measurement equipment,

you will be able to find these Nixie tubes used as a display, very, very popular.

A lot of people build very cool things with these like clocks or some

display depending on what kind of Nixie tube we can get a hold of.

I got a batch of 10 of them from eBay a while back.

I can't remember maybe about $50 or so.

Very cool things to play with but of course because they

need 150 volts or so to turn them on,

they are not the easiest things to use.

So, you will need a DC-DC converter.

So, I thought why not,

let's try and power one of these things using a flash circuit

because the flash circuit is capable of giving us that kind of voltages.

So, what I've done is that I've taken one of these guys,

and I have just placed that on

top of one of these breadboards so that all the legs are nicely separated.

There is a little resistors connected to the anode.

So, this wire right here is going to connect

to the anode and every one of the other wires,

the cathodes are going to be connected to

the potential that will turn it on and you should be able to see those numbers.

So, I'm going to connect everything up,

show you how it's connected, and then let's see if we can power it on.

Then, the last thing,

we're going to measure the efficiency of

the DC-DC converter based on how much power is delivered to the Nixie tube,

and how much power is required for the flash circuit to run.

So, let's do that.

So, let's see what I've done here.

I have connected the flash circuit to the power supply,

so it's powered on.

I'm monitoring the voltage of the capacitor

simultaneously like I was doing before on the multimeter.

I am connecting the anode to ground and I'm connecting one of

the cathodes to the negative terminal of the capacitor.

This is because, remember this produces

negative voltages with respect to the ground of the power supply.

So, at the same time,

I am measuring the voltage that is connected to the flash,

the current that's connected to this that it is being provided to the flash,

the voltage across the capacitor,

and the current that is given to the Nixie tube.

So, if I were to multiply this current by this voltage,

that's the power delivered to the Nixie tube.

If I were to multiply this number with this number,

that's the power delivered to the flash unit.

So, by dividing the result of this to this,

I can get the efficiency of the DC-DC converter afterwards.

But let's first turn on the Nixie tube and see what happens.

So, let me go all the way down and we bring the Nixie tube into view, like so.

I'm going to increase the voltage in the power supply until this guy turns

on. Here we go.

There we go. Here it is and it's showing the number eight.

I can show other numbers by connecting it to the other numbers.

For example, here's number two, three, four,

five, six, seven, eight,

and the back that's nine.

You can also turn one and other ones but I don't want to reach the back,

all the way back just in case I will short-circuit the wires.

So, let's connect it back to number eight.

So, the thing that makes this Nixie tube is really

cool is the fact that the numbers are not all on the same plane.

So, it gives it this weird 3D look.

As I go across the numbers,

the numbers go back and forth and I think that's

a really cool retro look and you could incorporate in one of your future projects.

So, you can see when we're a bit closer,

the number eight is glowing.

Very nicely, it has a very nice orange glow color to it.

So, I'm going to put this down on the ground,

leave this number eight on so we can measure now the efficiency of the DC-DC converter.

So, let's put this back down here.

While it's on, let's go up and look at these numbers. Here we go.

So, the power supply is set to 0.8 volts and is drawing 386 milliamps.

So, let's say for the sake of to make it easy in the calculation,

let's say this was 400 milliamps.

So, that will be 0.32 watts.

320 milliwatts of power is being delivered to the flash DC-DC converter.

The voltage across the capacitor is 133 volts, negative 133 volts.

The current going to the Nixie tube is 1.2 milliamps.

So, if you multiply 1.2 milliamps by a 133 and divide that by about 320 milliwatts,

you get just over 50 percent.

So, the efficiency, the DC-DC converter efficiency for turning one of these Nixie tube

on using a flash from a disposal flash camera is only about 50 percent,

which is very bad because you can make

DC-DC converters that are easily more efficient than 80 percent.

But, for hacking purposes and for something

that would have otherwise been thrown out and for educational purposes,

I think this is a great project that

if you have some experience dealing with high voltages,

I strongly recommend that you try it out.

Especially, if you've never played with Nixie tubes,

this things are really, really neat and they're not that expensive.

You can get them in all kind of patterns.

Doesn't have to be numbers.

Sometimes you can have them as bars or something else.

So I strongly recommend that you try this out, and then you see what you can do with it.

Just be very, very, very careful.

>> Well, I hope you enjoyed this episode playing with flash circuits and

Nixie tubes and I hope that we learned a thing or two about how these things operate.

Unfortunately, I'm going to have to break this video up again into

multiple sections because YouTube doesn't allow

me to upload anything that's more than 15 minutes.

But if you guys watch these videos and upper rank them,

then YouTube will eventually allow me to put

the entire episode in one video so you don't have to keep clicking.

So, please make sure you discuss this in

the comment section and also don't forget to answer

the quiz that I asked about why the neon light flashes as opposed to LED that doesn't?

Whoever gets the answer right,

will choose the next topic of the next episode.

We have a lot of videos,

a lot of equipment to review,

and a lot of interesting things coming in the future.

So, make sure you check back,

subscribe and I'll see you soon.