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HIGH-VOLTAGE Homemade exposure unit UV-RADIATION

made from an old face tanner

(from Matthias Franz, HB9EFY)

translation from the German original




The face tanner

Picture 1 shows the opened Tshibo®™ face tanner which I bought for less then 10 USD from Ebay®™. I bought a second, identical one from Philips®™, to have some spare UV tubes.

In the face tanner the 6 uv tubes (15 watt each) were placed curved in front of a silver reflector. As the whole face tanner case is far away from being user friendly, I decided to re-build the complete electronic into a new case.

I therefore, after disconnecting the power plug, removed all uv tubes, the tube sockets, the fluorescent starters and the 3 magnetic ballasts

ATTENTION: see Safety instructions and disclaimer !
[01]: original exposure unit)
[01] opened face tanner

[02a]: exposure unit - rebuild)
[02a] starting to rebuild
[02b]: exposure unit - rebuild)
[02b] mounting the tube sockets

Picture 2a shows the rebuild on a plywood sheet whereas picture 2b shows in detail how the tube sockets were mounted.

Each tub sockets has 2 plastic nibs on the back. For each socket I drilled 2 holes into circuit material. Then I pressed the socket nibs into the drill holes. Finally I screwed the stripe of epoxy circuit material to the wood slat.

The wiring diagram to drive 1 or 2 tubes is printed on the top of the magnetic ballasts (see picture no. 14). In my case every magnetic ballast is driving 2 tubes. In addition every tube needs of course its own fluorescent starter.



Picture 3 shows the completed rebuild with all tubes, magnetic ballasts and fluorescent starters.

The 4 starters in the right upper corner as well as the 2 vertically mounted magnetic ballasts are connected to the 4 top uv tubes. The 2 single starters at the right bottom as well as the horizontal mounted magnetic ballast driving the 2 lower uv tubes.

To wire all parts together I used 0.75 mm² strand cable which I tinned at the ends. This was required as all parts had these clamp connectors (without any screws). To make the wiring look a little bit nicer I used quite some hot glue.
[03]: exposure unit - rebuild completed)
[03] rebuild completed

[04]: exposure unit - 1st test run)
[04] 1st test run

Picture 4 shows the first test run.

The tubes need approx 2 seconds to ignite. You can see on the photo that one end of the tube is actually a bit brighter than the other end. However - as the board is supposed to be placed in the middle I do not expect any quality problems.

(By the way: if you know why the tube's one end is brighter than the other one - please drop me a note).

Now as the electric is working, let's move-on and build the remaining parts of the exposure unit.

[05]: exposure unit - additional layer)
[05] additional layer of wood slats
[06]: exposure unit - painted)
[06] painted in black

Picture 5 shows the rebuild with an additional layer of wood slats screwed to the first layer. The top wood slats will later on carry the pane of glass.

Picture 6 shows actually the same but the wood was painted in black now (a bit of isopropanol and few drops of refill ink for a black Edding®™ pen, as this mixture is drying very fast. Don't forget to open the window!)

The base plate will later on be covered by a white mat carton (as a kind of reflector). The side walls will stay painted in black to avoid potential light scatter.

[07]: exposure unit - timer prototype)
[07] prototype of the timing device
[08]: exposure unit - timer prototype)
[08] prototype of the timing device

The timing device

The timing device was made with a Atmel®™ ATmega32 microcontroller. Picture 7 and 8 shows the prototype of the timer using an Atmel evaluation board from Pollin Elektronik®™ (green board) and my own test board.

My homemade test board contains a 2*16 LCD display, a pot for the LCD contrast, rotary encoder, 10 LEDs, a pot for A/D tests and several push-buttons. All parts can be connected via cable bridges with all microcontroller ports.

The code for the timer was written in BASCOM AVR®™ Basic. The controller was programed with a serial device programmer called PonyProg®™ (to use the Pollin evaluation with PonyProg please I used the following settings).

Picture 10 and 11 shows the final timer build as ugly construction on a strip board.

The circuit

Picture 9 shows the timer's circuit diagram. Basically it contains only of an ATmega, a LC-display, a rotary encoder and a relay as switching stage.

The LCD was connected to the ATmega exactly as discribed in the BASCOM AVR application notes. The rotary encode I use has a build in push-button but you can use an external one as well to start the timer.

For the switching stage a 6 volt relay was used. Don't forget the fly back diode to protect the transistor powering the relay. The series resistor for the transistor stage should be about 10% of the expected collector/emitter current.


[09]: exposure unit - circuit diagram)

[9] circuit diagram

[10]: exposure unit - final timer bottom)
[10] final timer (bottom)
[11]: exposure unit - final timer top)
[11] final timer (top)

With the rotary encoder the exposure time can be chosen in steps of 5 seconds. When pressing the button build into the rotary encoder the countdown starts. To stop or restart the countdown press the reset button.

When pressing the start button the chosen exposure time will be stored in the eeprom of the ATmega. After resetting the counter or re-powering the value of the stored exposure time is read from the internal eeprom and used as new start value. No need to write down or remind the exposure time - the counter stores the value for you.

Example with a stored start value of 105 seconds:

[11a]: exposure unit - timer functions)
Display shows the start value of 105 seconds.
To start countdown press the start button.

[11b]: exposure unit - timer functions)
Timer was started. Countdown backwards to zero.

[11c]: exposure unit - timer functions)
Time elapsed.
To reset the counter press the reset button.

The code

The code written in BASCOM AVR Basic can be found here. The code contains quite a lot of comments and is hopefully self-explanatory. To generate the 1 second cycle the timer1 of the ATmega32 was used.

Time1 creates a reproducibly and for this purpose precise enough accuracy. If you are a high-precision fetishist feel free to program it in assembler. This program for the timer needs only 5% (~1kb) of the available 32kb of the used ATmega32. You can therefore program the microcontroller with the free version of the BASOM AVR controller (the free version is limited to 4kb). I finally used an ATmega32 because it was simply the first one I found in my spare part box.

NOTE:
In case the program reacts like in slow motion - please check the security bits and ensure you're not using the internal crystal. In case you're using PonyProg to program the ATmega32 microcontroller these are the settings I used.


Weaknesses of this simple program:

  • The BASCOM internal instruction to read the rotary encoder is rather slow. If you turn the encoder too fast the microcontroller may drop single steps.
  • Programming in BASIC is nothing for high-precision fetishists. But this is not a reference clock but a simple countdown timer only.
  • If you power-on the device the mechanical rotary encoder sometimes generates an impulse which leads to the fact that the start value of the counter can be +/- 5 seconds of the originally stored value.


[12]: exposure unit - final assembling)

[12] the final assembling

The final assembling

Picture 12 shows how the bottom part of the exposure unit is built into the aluminuim briefcase. The upper part of the exposure unit contains the timer unit, the bottom part contains the uv tubes, the starters, the magnetic ballasts and the power supply for the timer unit. Both parts can be connected by 2 connectors. This makes it quite easy to disassemble the unit in case of any repairs.

This low price briefcase is not completely made of aluminium. The edges of the briefcase are however indeed made of metal. In case of a malfunction this could potentially lead to a dangerous electro shock. To avoid this, the metal parts of the briefcase were connected to the protective earth conductor. Details can be seen in picture 14 (in Germany this cable is coded in "green-yellow").


Picture 13 shows how the top sheet was built. It contains of 2 layer of plywood sheets and the pane of glas.

The whole cutted into the plywood sheet number 1 is on every side about 2cm wider than in the sheet number 2. Plywood sheet 1 and 2 were finally glued together and screwed to the wood slats (picture 5 & 6).

Picture 15 shows the power supply for the timer unit. I used the inner parts of an old 12 volt wall wart and soldered it on a piece of strip board.

As the wall wart is a 12 volt type but the ATmega required 5 volt I added a voltage regulator to the timer unit (which is not shown on the circuit diagram).

[13]: exposure unit - top sheet)
[13] top sheet

[14]: exposure unit - protective earth conductor)
[14] protective earth conductor
[15]: exposure unit - timer power supply)
[15] power supply for timer unit

The final product

Picture 16 and 17 are showing the final exposure unit built into the briefcase.

The labeling of the control element was done as for all my projects:

  • Labeling and background color was printed on a simple paper label
  • Self-adhesive transparent foil as protection layer
  • Cutting vents for the display, button and rotary encoder with a box cutter
Keep in mind that the 6x 15 watt tubes become after some time quite hot. In case of long exposure times adding an e.g. processor fan and several vent holes might be a good idea.

[16]: exposure unit - final exposure unit 1)
[16] final exposure unit (1)
[17]: exposure unit - final exposure unit 1)[16]: exposure unit - final exposure unit 2)
[17] final exposure unit (2)



Corrections and ideas


Please let me know in case you find some mistakes in the program code or in the circuit. Any additional constructive criticism is welcome as well.

I hope that the description of my project may help you to realize your own exposure unit.


Greetings from Switzerland
Matthias, HB9EFY

[ HB9EFY(at)yahoo.de ]

to see this video you have to activate javascript and you need to install the Adope flash player ®™


Feedback:

The boss of www.intotheblue.ch contacted me and has sent me some great pictures of his own exposure unit project. Thanks for your nice feedback. I hope to talk to you via 2m one day.



Source:

Pollin Elektronik:
- Atmel Evaluationsboard V2.0
- Atmel Mega32
- Rotary encoder
- LC-display
- Reset button

Reichelt Elektronik:
- Electronic small parts

Ebay:
- Face tanner

DIY store:
- Wood slats, plywood sheed
- Pane of glass (picture frame 20x30cm)
- Aluminium briefcase

Copyright:

The text and pictures of the "
Homemade exposure unit " - project (except the PonyProg screen shoots) are copyright protected by endorphino.de (Matthias Franz) in December 2007.

The following names:
HELVAR ®™,
Pollin Elektronik ®™,
Ebay ®™,
Edding ®™,
Reichelt Elektronik ®™,
Philips ®™,
Tchibo ®™,
PonyProg ®™,
Adobe Flash Player ®™,
Bascom AVR ®™ and
Atmel ®™ are protected trade names and/or registered trademarks.

The video player JW FLV MEDIA PLAYER is licensed as Creative Commons.

Usefull links (in German only):


Basics"ATmegas and BASCOM AVR":
Web site from Thomas in Hamburg/Germany http://www.dieelektronikerseite.de

Basics"The timers of the ATmegas & BASCOM AVR":
Web site "Roboternetz" http://www.roboternetz.de/wissen/index.php/Bascom_und_Timer

Basics"How to connenct a LCD to an ATmega & BASCOM AVR":

Web site "Roboternetz" http://www.roboternetz.de/wissen/index.php/Bascom_und_LCD's


Safety instructions and disclaimer:

  • The ultra violet radiation of the uv-tubes could irreversible harm the eyes and skin of humans & animals. Ensure you take approbriate safety precautions.

  • The power supply could cause serious injury or death if proper precautions are not taken.

Build and/or use at your own risk. Matthias Franz cannot be held liable or responsible or will accept any type of liability in any event, in case of injury or even death by building and/or using or misuse of this project/information or any other projects/information posted on endorphino's web site.

By accessing, reading, and/or printing the articles presented here you agree to be solely responsible as stated in this disclaimer and exempt Matthias Franz from any criminal and/or liability suit.

Safety is a primary concern when working with high voltage and/or ultra violet radiation.

Play it safe.






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