Photography-equipment-friendly UV torch

[Andrea B.]

Akira, what a cool build! I like that it is fitted to the camera. As you mentioned, hand-holding the torch can be difficult for fluorescence or reflectance work.

 

Dr. Klaus once built me a nice UV-led torch which fitted into the hot-shoe via a microphone holder which he happened to find. 

 

Akira, I have a question. If somebody else saw your post and wanted to build a similar torch, is the information in the original (first) post sufficient for a safe build? I ask this because I only know rudimentary electronics and did not fully follow the discussion with Ulf. 

[Akira]

A 1 1/4" extension tube and a 28mm ZWB2 has arrived.  As I bought ZWB2 as the glass only, I added a cheapo 1 1/4 filter to use its ring as mount for ZWB2.

 

Originally I had planned to glue the tube with epoxy but decided to fix it with the Permacel tape in case I would have to replace the LED.  The filter on the right is Baader U.

[Akira]

12 hours ago, Andrea B. said:

Akira, what a cool build! I like that it is fitted to the camera. As you mentioned, hand-holding the torch can be difficult for fluorescence or reflectance work.

 

Dr. Klaus once built me a nice UV-led torch which fitted into the hot-shoe via a microphone holder which he happened to find. 

 

Akira, I have a question. If somebody else saw your post and wanted to build a similar torch, is the information in the original (first) post sufficient for a safe build? I ask this because I only know rudimentary electronics and did not fully follow the discussion with Ulf. 

 

Andrea, thank you for kind words!

 

The discussion between Ulf and me was mainly on the amount of the current that could be allowed to flow in the circuit.  As you would already know, there is always a bit of margin for the sample variation, the worst case design is preferable.  In this case, it would be safer to assume that the forward voltage (Vf) of your sample is at the minimum value of 3.5V, and use the resistor of 1.5 ohm, if you use a 5V power supply.

 

As mentioned in my initial post, a 3W resistor is safe enough, but you would have to combine more than one resistor to achieve the targeted 1.5 ohms.

 

My knowledge about the electronics is also just rudimentary.  But the most essential data you need to check out in the data sheed (PDF uploaded in the previous page of this thread) is the DC Forward Current in the Absolute Maximum Rating table and the minimum value of the DC Forward Voltage in the Electrical-Optical Characteristics table.

 

Other than that, the Ohm's law (R=E/I) is the only formula to figure out the value of the resistor.  In this case, (the power source of 5V and the  Forward Voltage is 3.5V), the formula would be (suppose the current is set to 1A):

 

R=(5-3.5)/1=1.5

[otoien]

A concern could be that the power supply has its negative side referenced to the metal chassis of the case, so if one gets any short of the live AC side of the power supply to DC ground one could get a shock. Best to pay attention to use a safe power supply or run it off batteries.

 

No home built electronics is safe - among long term hobbyists, who has not smoked a tantalum capacitor or two      .  It can be quite impressive!

[Akira]

1 hour ago, otoien said:

A concern could be that the power supply has its negative side referenced to the metal chassis of the case, so if one gets any short of the live AC side of the power supply to DC ground one could get a shock. Best to pay attention to use a safe power supply or run it off batteries.

 

No home built electronics is safe - among long term hobbyists, who has not smoked a tantalum capacitor or two      .  It can be quite impressive!

 

Thank you for the note.  I use an AC/DC adapter of a switching regulator type.  The negative side of the DC input jack is grounded to the case.

 

I've been using many guitar/bass effect pedals whose DC inputs from 9V AC/DC adapters (conventional rectifiers and switching regulators) whose negative sides are grounded to the case, which has been a common practice throughout the world for decades.

 

The only case to be cautious about is when you use vintage booster or fuzz pedals using germanium transistors whose positive side is grounded to the case: you should never share the power with other pedals with its negative side grounded.

 

This UV-LED torch is powered and wired in the same way as the most common effect pedals, and I'm not really concerned about the electric shock.

 

Tantalum capacitors are dangerous because they would break in the way that both terminals are shorted!

[Akira]

Here's a rather entertaining cases of the exploding capacitors.

 

 

[otoien]

Great fun and fancy camera. The capacitors look like electrolytic ones. It does not take much voltage to blow up the Tantalium ones, just mess up on polarity when mounting them. I had a project where I blew up two large surface mount ones before realizing that the manufacturer used unusual polarity markings... As I recall I had to redo the whole board...

[Akira]

3 hours ago, otoien said:

Great fun and fancy camera. The capacitors look like electrolytic ones. It does not take much voltage to blow up the Tantalium ones, just mess up on polarity when mounting them. I had a project where I blew up two large surface mount ones before realizing that the manufacturer used unusual polarity markings... As I recall I had to redo the whole board...

 

Oh, sorry about that.  I would have to admit that there are always potential danger in DIY products, which is the baseline.  I decided that my UV-torch is usable enough based only on my user experiences of the similar products that are professionally designed.  At the end of the day, such products should be used at one's own risk.