Recomend a hall affect for AC detection

oracacle

Senior Member
I have been playing around with the dangerous side of electricity, as safely as I can.
I have been photographing exposed light bulb elements - yes I am very careful, I ensure that the lamp is unplugged when installing and removing bulb with the glass removed.
The attached shot was taken with a photo transistor but feel its missing the initial demise of the filament.
So I thought about using a hall affect to detect when the lamp is switched on. the camera take about 0.045 seconds to take the first shot so hopefully detection pf the AC current in the wire will be fast enough to get the start of things.

I have an allegro 3144 which I tried but does not seem to detect anything in the when current passes through the wire.
I have looked through a few but I cant figure out which would be best.

unless there is a batter way that does not involve cutting open the wire - don't fancy that myself.

Thanks
 

Attachments

JimPerry

Senior Member
How about reversing it - use a Solid State Relay (SSR) to turn power on and control it and camera from Picaxe :confused: Then camera can be fine tuned to start before power ...
 

oracacle

Senior Member
would that not mean cutting into the ac lamp wire? The thought has crossed my mind, then came the thoughts of using different lamps, so different wire would need modifying.
However I suppose if I were to make up and extension type arrangement with the relay in it I could avoid modding everything I want to mess around with
 

techElder

Well-known member
I once did a study on "inrush current" on tungsten filament bulbs.

The conclusion was that filaments that aren't switched at the zero-crossover point of the applied AC (when the filament is cold) don't last nearly as long. As it turned out at the time, the filaments get hotter at points where there are impurities manufactured in.

Switching at the zero-crossover point limits the "inrush current". (Inrush current is maximized when the filament starts cold.)

I don't know if you are trying to photograph a burning out filament or not, but thought I'd share my experience on the subject.

As far as cutting the lamp wire, your idea of an extension with a box of receptacles makes sense. If you add an isolation transformer inside the box, you will be making yourself much safer, too.
 

oracacle

Senior Member
the intention was burning filament.
I made a small change to the photo transistor light detector that I was using and gained some results.
I ensure that I unplug the lamb before doing any thing, the switch in the wire that many lamps come with is always switched of to stop mistake in safety too.
I will look into the little box of tricks.
 

fernando_g

Senior Member
oracacle;
first of all very nice photograph! I can appreciate the time and effort required to achieve the required effect.
Some years ago, I was also very interested in that type of photography, see the attached image.

Does your camera have an auxiliary input where you can trigger the shutter? I'm very interested in the details. And those 45 milliseconds that you quote, is the actual "shutter delay" from the time of the trigger?

But to your question.....
The ACS712-series of hall sensors are very dependable, I've used them successfully for a number of projects. The no-current output voltage sits at 2.5 volt, so you will need a comparator to detect when the voltage swings outside that value. The comparator will then trigger your camera.

cerillo1.jpg
 

SteveDee

Senior Member
...I have been photographing exposed light bulb elements - yes I am very careful...
Wow! what a great shot!

Unfortunately my wife is looking over my shoulder, and now wants me to Picaxe her Pentax K3.

I guess if you want full control, such that you can pre or post trigger with a repeatability down to a couple of milliseconds, you probably need parallel control of camera and action with a 'detonator' switch (e.g. you press a switch which fires camera and powers bulb with individual delay settings). The mains probably needs switching via a zero-crossing solid-state switch.

However, I wonder how much delay there is in a simple power supply (like a phone charger). If you could use the low dc voltage from the power supply to trigger you camera when power is applied to both power supply & bulb....
 

oracacle

Senior Member
If you where to have a switch on the input side of the relay which which also goes to the picaxe (a simple double throw switch) and the switch side of the relay controlling the ac to the lamp.

I can post up the latest version of code if you want to have a go at building the controller. It has some nice features now including a time lapse timer and shutter timer. It can also control the flash via a modified flash extension cable and has a torch output.

I used a hacked wired shutter release to interface with the camera, if you decide to go ahead and picaxe the wifes camera I would suggest going the same way - it makes interfacing easy.
 
Last edited:

fernando_g

Senior Member
I used a hacked wired shutter release to interface with the camera, if you decide to go ahead and picaxe the wifes camera I would suggest going the same way - it makes interfacing easy.
I'm interested on that, as on my Fuji the only way to remote trigger it is with an old fashioned shutter release...can you share how you did it?
 

oracacle

Senior Member
Do you mean the mechanical cable, if so I'm not sure i can help. But the you're that you plug in with electrical contacts is as easy as opening it up. Mine had two spring contacts and a fixed one. The top one was common, the middle was focus and the bottom fixed one was shutter.

If you have a mechanical shutter a servo or motor with cam could be used to operate the shutter release.

When i said a wired shutter i meant as apposed to a remote shutter that uses ir
 
Top