# Zero Parts-Count Temperature Sensor

Quick: What’s the forward voltage drop on a conducting diode? If you answered something like 0.6 to 0.7 V, you get a passing grade, but you’re going to have to read on. If you answered $V_F = \frac{T-T_0}{k}$ where T0 and k are device-specific constants to be determined experimentally, you get a gold Jolly Wrencher.

[Jakub] earned his Wrencher, and then some. Because not only did he use the above equation to make a temperature sensor, he did so with a diode that you might have even forgotten that you have on hand — the one inside the silicon of a MOSFET — the intrinsic body diode.

[Jakub]’s main project is an Arduino-controlled electronic load that he calls the MightWatt, and a beefy power MOSFET is used as the variable resistance element. When it’s pulling 20 or 30 A, it gets hot. How hot exactly is hard to measure without a temperature sensor, and the best possible temperature sensor would be one that was built into the MOSFET’s die itself.

There’s a bunch of detail in his write-up about how he switches the load in and out to measure the forward drop, and how he calibrates the whole thing. It’s technical, but give it a read, it’s good stuff. This is a great trick to have up your sleeve.

And if you’re in the mood for more stupid diode tricks, we recommend using them as solar cells or just stringing a bunch of them together to make a thermal camera.

# Hackaday Prize Entries: Inventing New Logic Families

One of the favorite pastimes of electronics hobbyists is clock making. Clocks are a simple enough concept with a well-defined goal, but it’s the implementation that matters. If you want to build a clock powered only by tubes and mains voltage, that’s a great skill tester. A relay-based timepiece is equally cool, and everyone should build a Nixie tube clock once in their lives.

For [Ted]’s Hackaday Prize entry, he’s building a clock. Usually, this would be little cause for celebration, but this is not like any clock you’ve ever seen. [Ted] is building this clock using only diodes, and he’s inventing new logic families to do it.

Using diodes as logic elements has been around since the first computers, but these computers had a few transistors thrown in. While it is possible to make AND and OR gates using only diodes, a universal logic gate – NANDs and NORs – are impossible. For the computers of the 1950s, that means tubes or transistors and DTL logic.

For the past few years, [Ted] has been working on a diode-only logic family, and it appears he’s solved the problem. The new logic family includes a NOR gate constructed using only diodes, resistors, and inductors. The key design feature of these gates is a single diode to switch an RF power supply on and off. It relies on an undocumented property of the diodes, but it does work.

Although [Ted] can create a NOR gate without transistors — a feat never before documented in the history of electronics — that doesn’t mean this is a useful alternative to transistor logic. The fan-out of the gates is terrible, the clock uses about 60 Watts, and the gates require an AC power supply. While it is theoretically possible to build a computer out of these gates, it’s doubtful if anyone has the patience to do so. It’s more of a curiosity, but it is a demonstration of one of the most mind-bending projects we’ve ever seen.

You can check out a video of the diode clock below.

# Home Brew Vacuum Tubes Are Easier Than You Think

It all began with a cheap Chinese rotary vane vacuum pump and a desire to learn the witchcraft of DIY vacuum tubes. It ended with a string of successes – a working vacuum chamber, light bulbs, glow tubes, diodes, and eventually this homebrew power triode and the audio amplifier built around it.

[Simplifier]’s workshop seems like a pretty cool place. It must have a bit of an early 20th-century vibe, like the shop that [John Fleming] used for his early work on vacuum tubes. Glass work, metal work, electronics – looks like [Simplifier] has a little bit of everything going on. True to his handle, once [Simplifier] had a cheap but effective vacuum rig he started with the easiest projects – incandescent and gas discharge lamps. Satisfied that he could make solid electrical and physical connections and evacuate the tubes, he moved on to diodes and eventually triodes. The quality of the tubes is pretty impressive – stray gasses are removed with a bake-out oven and induction-heated titanium getters. And the performance is pretty solid, as the video below reveals.

Very impressive overall, and it’s not just the fact that he’s building tubes from scratch – we’ve seen that before. What shines here is that specialized equipment is not needed to make working and reliable tubes – just a MAPP torch, simple hand tools, and a low-end vacuum rig. Anybody could – and probably should – give this a try.

# Home Made Diodes From Copper Oxide

We’re all familiar with semiconductor devices, and we should remember the explanation from high-school physics classes that they contain junctions between two types of semiconductor material. “N” type which in the for-schoolchildren explanation has a surplus of electrons, and “P” type which has “Holes”, or a deficit of electrons.

Unless our careers have taken us deep into the science of the semiconductor industry though that’s probably as close as we’ve come to the semiconductors themselves. To us a diode or a transistor is a neatly packaged device with handy wires. We’ve never really seen what’s inside, let alone made any real semiconductor devices ourselves.

[Hales] though has other ideas. With the dream of creating a paintable semiconductor layer for ad-hoc creation of simple diodes, he’s been experimenting with oxidising copper to make a surface of cupric oxide onto which he can make a contact for a simple diode.

What makes his experiments particularly impressive though is not merely that he’s created a working diode, albeit one with a low reverse breakdown voltage. He’s done it not in a gleaming laboratory with a full stock of chemicals and equipment, but on his bench with a candle, and drops of water. He takes us through the whole process, with full details of his semiconductor manufacture as well as his diode test rig to trace the device’s I/V curve. Well worth a read, even if you never intend to make a diode yourself.

We’ve featured a cuprous oxide diode once before here at Hackaday, albeit a rather fancier device. If this article has piqued your interests about diodes, may we direct you to this informative video on the subject?

The diode looks black, leading me to believe it’s cupric oxide and not cuprous oxide. Feel free to argue that point in the comments anyway – Ed.

# Sciencing DVD-RW Laser Diodes

If you’ve played around with laser diodes that you’ve scavenged from old equipment, you know that it can be a hit-or-miss proposition. (And if you haven’t, what are you waiting for?) Besides the real risk of killing the diode on extraction by either overheating it or zapping it with static electricity, there’s always the question of how much current to put into the thing.

[DeepSOIC] decided to answer the latter question — with science! — for a DVD-burner laser that he’s got. His apparatus is both low-tech and absolutely brilliant, and it looks like he’s getting good data. So let’s have a peek.

First up is the detector, which is nothing more than a photodiode, 100k ohm load resistor, and a big capacitor for a power supply. We’d use a coin-cell battery, but given how low the discharge currents are, the cap makes a great rechargeable alternative. The output of the photo diode goes straight into the scope probe.

He then points the photodiode at the laser spot (on a keyboard?) and pulses the laser by charging up a capacitor and discharging it through the laser and a resistor to limit total current. The instantaneous current through the laser diode is also measured on the scope. Plotting both the current drawn and the measured brightness from the photodiode gives him an L/I curve — “lumens” versus current.

Look on the curve for where it stops being a straight line, slightly before the wiggles set in. That’s about the maximum continuous operating current. It’s good practice to de-rate that to 90% just to be on the safe side. Here it looks like the maximum current is 280 mA, so you probably shouldn’t run above 250 mA for a long time. If the diode’s body gets hot, heatsink it.

If you want to know everything about lasers in general, and diode lasers in particular, you can’t beat Sam’s Laser FAQ. We love [DeepSOIC]’s testing rig, though, and would love to see the schematic of his test driver. We’ve used “Sam’s Laser Diode Test Supply 1” for years, and we love it, but a pulsed laser tester would be a cool addition to the lab.

What to do with your junk DVD-ROM laser? Use the other leftover parts to make a CNC engraver? But we don’t need to tell you what to do with lasers. Just don’t look into the beam with your remaining good eye!

# Take the Long Road to a Precise Laser PCB Exposer

According to [diyouware], inside of every HD-DVD player is a gem of laser engineering with the designation of PHR-803T, and it’s just begging to be converted into a PCB exposer. Following along similar hacks which tore the laser diode out of Blu-ray players to expose PCBs, they wanted to use the whole PHR-803T unit without disassembling it, and to try to enable all of its unique features.

They envisioned something simple like a scanner for their machine. Just place the PCB on top of a glass sheet, close the lid, and click print. Unfortunately, moving the laser itself just caused too much vibration. So they switched to an inverted delta robot and named it TwinTeeth. In this design, the laser would stay still and the PCB would move.

What follows next is a seriously impressive journey in reverse engineering and design. The PHR-803T had no data sheet, but a ton of features. For example, it can autofocus, and has three different laser diodes. So many interesting problems were found and solved. For example, the halo from the laser caused the surrounding photoresist to cure. They solved it by adding a glass plate with a UV filtering film on it. Only the most focused point of the laser could punch through.

Another adventure was the autofocus. They wanted to autofocus on all four corners of the board. The PHR-803T was designed to read HD-DVDs so can focus a beam to far below 0.01 mm. They got autofocus working with the UV laser, but couldn’t use it on the PCB without curing the photoresist. So they put a piece of aluminum foil at a known level to start. Then they realized they could use the red or infrared diodes to focus instead. Now they can level the PCB in software, and focus the diode without curing the photoresist.

In the end they have an inverted-delta mini PCB factory. It can produce boards around the size of an Arduino shield with a resolution of 600 DPI. Their machine also has attachments for drilling and solder paste dispensing. Check out the video of it in action.
Continue reading “Take the Long Road to a Precise Laser PCB Exposer”

# An Introduction To Zener Diodes

[Afroman] is back again with another great tutorial video on the basics of electronics. This time it’s zener diodes.

Page three or four of every ‘beginners guide to electronics’ covers a diode as, “a component that only allows current to flow in one direction.” This is true; a diode only allows current to flow in one direction. However, like any depth of knowledge, the dialectic of diodes quickly turns to a series of, ‘but..’ and ‘however…’ statements.

A zener diode is like a normal silicon diode, where a forward biased diode will pass current with a ~1 volt drop. When a zener diode is reversed biased, there’s a different voltage drop, annotated as Vz on the datasheet. When reversed biased, current cannot flow across the diode unless the voltage is above Vz. This is what makes zeners useful for a bunch of applications.

[Afroman] goes over a few of the most useful applications of zeners, including a diode clamping circuit. This circuit will clamp the voltage to a maximum of Vz, helpful when you’re feeding a signal into an analog input. This voltage clamping circuit can be used in some interesting applications. If you feed a sine wave or other signal though the circuit, you can clip the signal.

Zeners can also be used as a very crude, low current, low accuracy power supply. If you’re looking for a voltage regulator for a microcontroller that’s impossibly easy and you’re all out of 7805s, pick up a zener. It’s not the basis of a good power supply, but it does work.