monspace

Single LED UV PCB exposure box

2010-11-28T01:23:00.011+01:00

PART LIST:

1 UV LED
1 LM117 (TO3)
1 RESISTOR 1ohm 2W
1 Piece of wood
1 Piece of Aluminium
1 Piece of plastic (transparent)
2 magnets

Having seen several attempts to make a PCB exposure box with LEDs instead of tubes, i decided to make my own.

I wanted a smal one because i make prototypes one of a kind pcbs, and they are always small.
One wich could hold an arduino shield would be large enough.
Other projects i saw are using a large number of low power uv leds wich are in the miliwatt range. 80 Leds seems to be the minimum number to achieve 1W of UV radiated power, wich is what is needed to expose the PCB in a decent time.
This big number of leds needs a big PCB with a big number of holes and solder, and i don't like holes !

So i decided to use a single high power UV led.

The LED is 5W and is the higest power i could find at an affordable price.
It can output up to 1.5W of 400 nm UV radiation at 1500mA.
With high power leds, you should not mess with the current, moreover if you want to push it to the limits. If you go over 1.5A, it will bee VERY hot and its life much shorter than the expected 100.000 h. If you go below, you will have only a fraction of the expected output.
Never use a constant voltage driver, but use a constant curent one.
For this first test, i used a simple classic linear curent injector with a LM117.

This is the schematic of this simple regulation

The Vin supply comes from a wall adapter and can bee between 7V and 12 V DC with at least 1.5A. With 12V the LM117 can become quite hot without a heatsink, but it is ok because it is not used for a long time. A switching regulator would be better, but our main goal was simplicity.

The "mechanical" part is also very simple.

I cut a wooden board 16 X 16 cm for the base, and in the center i made a recess to accommodate the PCB. I did fill this recess with foam slices to press the PCB against the cover when it is closed.
The cover is a 8 X 14 cm acrylic rectangle inserted in an aluminium tube which serves as a hinge.
A magnet is inserted in the base and another on is glued to the cover.

Support for the LED, which is also its heatsink, is made from a folded piece of aluminum. The LED is screwed at the top. The aluminium plate is the ground return, there is only one wire going to the led.

The LM117 is glued to the board upside down and the 1 ohm resistor is soldered directly on it.
A power switch is also glued on the base and a DC jack for the power supply.

This first "proof of concept" has no timer built in, but this will be added in the next release with the help of a Tiny45.

I was really positively surprised by the result.
I used simple laser printed transparent sheet and an exposure time of 2 min for the few tests i made.

First board is an arduino shield which has big traces and is easy, but the second one with 0.5mm pitch chip and 10 mils traces is a real test and was a 100% succes.

Thank you HackADay for posting this.

From the comments i read on HackAday, i must give some more details.
Of course, the UV light does not remove the copper !

I use Pre-Sensitised Copper-Clad Board.

After exposure i develop it (liquid NaOh diluted in water 1/10), about 1 min.

Next, i etch it with a 5/1 mix of HCL (chloridric acid) and H2O2 (oxygen peroxyd), 3 to 5 min.

The cheapest dual trace scope in the galaxy

2008-10-02T01:44:00.005+02:00

DIY

This submini USB scope is based on a Atmel Tiny45 cpu and cost less than 5€ with a homemade pcb

It has 2 analog inputs and can supply 5V ont the 4 pins header on the right. One of the inputs can be scaled down with the trim pot.
The firmware in the Tiny45 is written in C and compiled with Winavr and usb source code from obdev. As you can see, there is no crystal , the software sync the internal 16.5Mhz pll clock with the USB clock.
The cost with a home made pcb is around 5€.
Of course, do not expect 1Gs/s HID does not alow that data rate ! But it is using a 10bits AD.

It has been designed to plug into a project breadboard so there is no need for a power supply.
On this picture it is used to test a high precision light sensor.

It does connect to a PC with usb in HID mode, without the need to install any specific driver. Data are diplayed on the PC with .NET C# software. This is an exemple of my display programOf course you can write your own code to capture or display the datas

Here is the schematic, so simple !

Bill of material

1 Led (any)
1 R for led, from 220 to 470 ohm, smaller is brighter
2 R 68 ohm on USB D+ & D-lines
1 Pull up R 1.5K for USB device detection
2 Zener 3.6V for right USB signal levels
2 Bypass caps 100nf & 47uf
2 filter caps on analog inputs ( from 10nf to 470nf or nothing, up to you)
1 or 2 trimpots on analog inputs to scale your voltage to AD range (1.2V or 2.5V by software )
1 USB socket (A,B, mini, you chose)
1 Atmel Tiny45-20.

eagle files: usbscope-tiny.zip

Here is the C source for the firmware including usb lib and HID descriptors
firmwarev3.zip,
and for those who do not want to mess with compilers, the .HEX file ready to flash main.hex.
Do not forget to set the fuses for internal PLL clock

And last for today, the Windows display software UsbADC.zp i. There is no setup with it, so copy in a folder with the dll and try. It is .NET so you need the framework.

UPDATE: for all who requested the C# code for this app, here is the link usb-scope.zip done with Visual Studio 2005

Thanks for reading.

mon iphone du 20ème sciècle

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ma première calculatrice

2008-07-18T04:14:00.000+02:00

plusmoinsfoisdiviser

Mon premier PC

2008-07-18T04:09:00.000+02:00

OS: CPM
CPU:Z80 10Mhz BUS S100
64KRAM

POV

2008-07-18T04:05:00.000+02:00

et un effet POV à leds pour vélos

lecteur mp3 ZigBee

2008-07-18T03:55:00.000+02:00

Ce lecteur mp3 avec amplificateur 2X40W est piloté à distance par une liaison radio ZigBee

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2008-07-18T03:53:00.000+02:00

une version à 8 canaux stéréos indépendants

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tout en un, le lecteur mp3 est intégré au haut parleur

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CNC Retrofit

2008-07-18T03:42:00.000+02:00

Retrofit,
cnc 3 axes pilotées par un avr 8 bits,
lcd, pavé numérique PC.
fichiers GCode sur carte MMC
Moteurs pas à pas, drivers Gekko

2008-07-18T03:38:00.000+02:00

ARM 32bits,
petit mais costaud

player mp3

2008-07-18T03:32:00.000+02:00

mieux qu'un nipod, ultra miniature
avec carte SD ou MMC jusqu'à 8GB

Refroidisseur thermoélectrique pour bouteilles

2008-07-18T03:28:00.000+02:00

le plan top secret

2008-07-18T03:11:00.000+02:00

voici le plan, ATTENTION !! top secret,
ne le montrer à personne