Archive for Circuit

High Speed Air-gap Flash

A bullet hitting a solid brass rod.

If you just want to buy an assembled and tested airgap flash, I have made an updated versions that can be purchased at Information Unlimited.

In my quest to capture amazing high speed photographs I notice that when photographing shooting bullets the bullets were blurred. I found that standard xenon tube, which standard flashes use, is very bright for the energy put into it because of glowing xenon gas. The book Electronic Flash Strobe by Harold Edgerton explains all the calculations, but in practice this means all the flashes from Nikon, Canon and others that use xenon flash tubes have a minimum duration of 1/40,000th of a second. That’s fast enough for most things, but not for a shooting bullet travels around 1000 feet/second. In 1/40,000th of a second that bullet can travel about 1/3rd of an inch leading to blurry photographs of bullets.

To solve this I had to make a faster flash. I’m certainly not the first to do this. I think that was Harold Edgerton. He actually created a company called EG&G to sell a product called the 549 Microflash, but that company has been dissolved and the product discontinued. Sometimes you can still find these flash units on ebay, but the ones I saw were selling for $8K+. There is also a company called Prism Science Works making a modern version of these for researchers, but you’ll need really deep pockets to afford one of those. I saw directions on how to build one in the August 1974 issue of Scientific America and emailed Alan who had already built a few. After this research I realized I could build a sub-microsecond flash for just a few hundred dollars. A sub-microsecond flash means the flash duration is less than 1/1,000,000th of a second or about 25 times faster than a xenon flash.

Here is an image showing how an air-gap flash compares to a standard flash when photographing a 1000 feet/sec pellet.

I am a strong believer in sharing knowledge so I’ll explain how I made my air-gap flash, but I am knowledgeable with high voltage safety procedures. You should not build this because this flash will kill you. It really will. This flash requires charging a 35,000 volt capacitor that will easily kill a person for a single mistake. I have a safety checklist that I use ever time I plug in this flash and it still scares me. If it didn’t scare me then I shouldn’t be using it because this thing is dangerous. The below information is for educational purposes only. Do not build one! If you go against my advice and do build one, I am not responsible for any injury, death, or any other problems it causes.

Here is a list of the main parts I used to build my air-gap flash:

Here is an overall diagram of how all the parts fit together.

This is the schematic for the custom circuit board I made. Basically it doubles the 120V AC and uses an external signal to trigger the 45 kV transformer.

And here is a picture of my custom circuit board.

Here is a picture of the air-gap flash.

This shows what is plugged into the air-gap flash. 120V to run the 45K trigger transformer, 14V to charge the big capacitor, and a 3.5mm cable to use for triggering.

Here is a side view. Notice that the reflector has a thin sheet of Plexiglas over it to make cleanup easier. The metal reflector is also grounded in case the plexiglass tubes shatter, and they do shatter sometimes. I have found they last longer if I use latex gloves so no oils from my hands get on the glass tubes.

This is a close up of the glass tubes where the spark happens. The outer glass tube is just for protection and to reduce noise. The inner tube has the wire 45 kV trigger transformer inside. When that transformer is triggered the air ionizes and that cases the big capacitor to discharge in a 1.5 inch spark that creates the flash of light. To seal the inner tube I melt one end with a torch until it is sealed.

A top down view that shows how everything is connected.

This rod is very important. It is how I discharge the big capacitor after every use so I don’t die when I’m working on the flash.

Those extra wires and circles are there so I had an easy way to discharge the capacitor.

Note about using it with the Camera Axe. The Camera Axe only allows a trigger voltage of up to 20V. This has a trigger voltage of 240V so I needed to to put a high voltage protection circuit between this and the Camera Axe. There are many examples of these circuits on the web.

Here are a few results:

Glass rods being hit by a bullet.

A balloon being hit by a bullet.

Thanks Alan for your help and letting me use some of your amazing photos.

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Camera Axe 4

After six months of work, the fourth version of the Camera Axe is finally ready. For those new to the Camera Axe it’s a programmable camera and flash trigger with two sensor plugs that can be used for a wide range of sensors. It can do anything from timelapse to photographing a shooting bullet. For a little background information read about versions 1 and 3 of the Camera Axe. This version is open sourced under the Creative Commons Attribution NonCommercial 3.0 License. I do sell kits, assembled versions, and various sensors at my store.

Camera Axe Video:

Here is a list of improvements from version 3 to version 4 of the Camera Axe.

  • The screen is much larger and this makes the menuing system easier to use.
  • The case is is much nicer because I had custom cases made for this project.
  • Added two LEDs to indicate when the camera or flash is being triggered.
  • Much nicer 3.5mm jacks for the sensors and camera/flash plugs.
  • Added a dedicated external power plug for those wanting to use external power.
  • The buttons feel much nicer.
  • Batteries last four times longer.
  • A new microcontroller that has two times the space for more features in the future.
  • The software is a complete rewrite and has too many improvements to list, but I’ll mention the greatly improved intervalometer mode and the new fast trigger mode.
  • The kits are easier to assemble (no wires or drilling needed).

There’s more information information about sensors, reprogramming, flash/camera cables, and much more at

Here are a few images taken with the Camera Axe.

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A New PCB Manufacturer in Town

Back when I started needing a way to organize my circuit designs on something more permanent than a breadboard I used wire wrapping. This was probably only 10 years ago so wire wrapping was and still is rarely used, but I liked it. It got what I needed done in an easy and fairly durable way.

Over the past few years I’ve wanted nicer circuit boards for my personal projects. There are many ways to make your own circuit boards at home. I’m sure there are over 100 articles on hackaday explaining the various methods. I’ve never done this. It seems like a lot of work to make the circuit board and then drill it out. Plus when it’s done it’s missing the useful solder and stencil masks. The obvious advantage to doing it yourself is you don’t have to wait for it to get shipped back to you which tends to take 2-4 weeks unless you pay big $$$ to expedite the order.

A few years ago I ordered my first few circuit boards from Batch PCB. They are probably still the cheapest place to get single boards made. The way Batch PCB works is to batch up individual orders and then send a big order to Gold Phoenix. It takes them a few days to batch up the orders. A few days to cut the boards once they get them back from Gold Phoenix and an extra week of shipping. So this means it usually took about a month from when I ordered until when I got the order. Besides the longer order time the price was expensive as soon as you started ordering more than one or two boards.

Next I started placing orders directly to Gold Phoenix. If you start selling kits like I do they are a great supplier and I’ve been very happy with them. I always order 155 sq inches of PCBs from them. They have options for panelizing, but I never tried that since I’m usually ordering PCBs for kits. 155 sq inches of PCB usually costs $100-140 depending on the options I choose. I’ve gotten anywhere from 15 to 100 boards from this 155 sq inches depending on the PCB size. I’ve also found that if I need to order more boards they give me a decent discount. I’ve had cases when ordering more boards that they cut the cost to less than half the advertised price. I’ve gotten 1000s of PCBs from Gold Phoenix and haven’t had a bad one yet. The main thing I didn’t like about Gold Phoenix was that you sent them your Gerber files as a zip file in an email and then had to pay for it through the Paypal site. The delivery time was about 2 weeks from when I ordered which is a little faster than their website says.

Some of the PCBs I’ve ordered from Gold Phoenix.

About a month ago I found a new PCB manufacturer call PCBWing. I’ve only ordered one batch of PCBs from them, but they had the same great quality as Gold Phoenix. Their website was much nicer than Gold Phoenix since it had much more flexibility on order sizes and a nice a shopping cart that let you pay for your order right on the site. I feel their website cuts ordering time in half compared to Gold Phoenix. Most single boards would still be cheaper through BatchPCB, but they have the cheapest prices I’ve seen on the web for small(5) to larger(100s) quantities of PCBs. For instance I found when ordering 100 3″x4″ PCBs PCBWing’s normal advertised price is still about half the secret discounted price I could get from Gold Phoenix. After I submitted my first order, I emailed some suggestions to PCBWing on how they could streamline their online ordering even more and they implemented the ideas in 3 days. That’s amazing service and the reason I decided to write this blog post. Basically I think PCBWing is a great new PCB manufacturer and I think people who order PCBs online should consider them as an option.

The first prototype of a new version of my Camera Axe project. Don’t mind those blue wires. I added those to work around some bugs I made in designing this prototype.

That said there are a lot of PCB manufactures I haven’t tried and maybe some of them are great too. Ladyada has assembled a pretty good list here. Maybe she’ll add PCBWing soon.

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Photographing Splashing Droplets

Up until now I’ve been using a photogate sensor and the Camera Axe to take pictures of water and milk droplets. After some research I found manypeopleonline were using solenoid valves to create droplets and take pictures of them. The big advantage to this method is it’s easy to collide drops which is was very difficult and random using my old method. I decided I’d make a new valve sensor (pre-built version available here) for the Camera Axe and document how to make your own since I didn’t find any detailed instructions or part lists on the web.

Building It

I knew I wanted to have a way to trigger my camera on a fairly long exposure in a dark room (I use a 1 second exposure). Then make a water droplet. Wait a little while. Make a second water droplet that would collide with the first droplet’s splash. And then wait a little more until the collision before triggering the flash. With this in mind I started making the different pieces I needed and connecting them together.

The only new circuit I needed was a simple motor driver circuit to drive the solenoid. Below is the one I designed and here are the PCB files I designed in Eagle.

Valve Sensor Circuit

Next I had to find and order the parts.

After assembly here is what it looks like:

I also made a new version of the Camera Axe software with the valve sensor. You can download this new version (3.0.03) from

Using it with the Camera Axe

Plug your camera into Camera/Flash1. Plug your flash (or flashes using a splitter cable) into Camera/Flash2. Plug this new valve sensor into Sensor1. Below is a picture of my setup. It has two flashes, a camera, the Camera Axe, and the valve sensor.

Go to the valve sensor menu. Set drop1 size to a good starting size like 80. Set drop2 delay and drop2 size to 0 (we will start with only a single drop). Set Flash delay to around 200 ms. Then turn off the lights and press the “Set” button. This will trigger the camera and the flash. Now adjust the flash delay by 10 ms increments until you have a good droplet picture. Below is a video sequence of 20 images stepping through a milk drop splash. The images go from 220 to 420 ms.

If you want to do colliding drops timing is more complicated. As a starting point I’d suggest a drop1 size of 80, drop2 delay of 40, drop2 size 50, and a flash delay of 200 ms. Then adjust the flash delay until you find the time of collision. Then you can start adjusting other timing parameters to get all sorts of different types of pictures.

You can find lots of photos (including droplet pictures) on the Camera Axe flickr group. Below are a few of my favorites from yesterday.

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Electric Eel Wheel

The hardware and software for this project are shared under the Creative Commons Attribution 3.0 License.

The Electric Eel Wheel is a clever electric spinning wheel making it great for easily spinning the fiber of your choice into yarn! You can use a traditional wheel; however, there are many advantages of this electric wheel design. First of all, the Electric Eel Wheel is lighter and smaller than most spinning wheels making it easier to take your spinning with you.

This electric spinning wheel’s design is based on a Scotch tension design, so it is easy to vary the spin and weight of your yarn. You can easily adjust it to make fine lace yarn as well as softly spun bulky. Another nice feature of the speed control dial is that it can spin the bobbin forward or reverse. Most people in our testing lab appreciated the range of speed that this wheel offers.

For build guides, Eagle files, bill of materials, source code, and more visit the Electric Eel Wheel’s home page.

If you’re interested if purchasing a kit or assembled version of this project I sell them in my store.

Even if you’re not interested in spinning yarn there is nice motor controller design in this project.

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