Friday, April 29, 2011

405nm vs 445nm comparison

I've been a bit disappointed by the 445 nm diode so far. It's not really burning as well as the 405nm diode. So I decided to put down some estimates to see what is happening.

I was unable to focus the 445nm to a pinpoint as small as the 405nm. If I had to estimate it would be 0.4 - 0.6mm 'dot' for the 445nm vs a 0.1 - 0.2mm pin for the 405nm. Let's run with that:

  • 405nm dot has a surface area of about 0.13mm^2 (using 0.2mm diameter)
  • 445nm dot has a surface area of about 0.79mm^2 (using 0.5mm diameter)

  • Assume the 405nm (200mA) puts out at 225mW
  • Assume the 445nm (700mA) puts out 500mW

  • 405nm delivers 225mW/0.13mm^2 = 1730mW / mm^2
  • 445nm delivers 500mW/0.79mm^2 = 633mW / mm^2

So unless I can get the dot size down with the better lens the 445nm will have a hard time competing with the 405nm. This is consistent with my observations on the CNC so far.

Tuesday, April 26, 2011

445nm 1 Watt monster diode

The 445nm diode came in and I've hooked it up to the CNC. This diode is a multi-mode laser diode. This means that the dot will not be nice and round as with the 405nm diode, but it has some real power and durability. People seem to run these at about 1amp, where the diode delivers about 1Watt of laser power. That is not bad!

So as a slow start I raised the platform to be as close to the laser as I could focus the beam (to keep the dot as small as possible) and set the current to 400mA figuring I was going to get about 400mWatt of power, however at 400mA this diode barely burns paper! The 405 diode at 400mA rips through paper like butter, needless to say a bit disappointing.

A quick look at the amp vs power graph over at Laser Pointer Forums confirms that this diode takes a good amount of amperage just to get started. At 400mA we get about 250mW of laser power. Whereas the 405nm diode gave us 400-500mWatt.

Sadly I can't drive the power up too much further today as I am running out of juice on the power supply. That'll be the next improvement. So this diode should really shine with a bit more amperage.

I ordered a better lens from JayRob on the forums ($13) to see if I can get this laser focused nicely.

Monday, April 25, 2011

Stanham driver

To run a CNC laser you'll need a laser diode driver (current source) that can be modulated. I wanted a driver that can be modulated with an analog voltage as well in case I want to give EMC control over the laser power output. After some searching I settled on a modified StanHam. I changed the design by adding soft-start capacitors (though not tested yet) and made it all surface mount components and a beefier output transistor as I intend to run this up to one amp for my 445nm diode. The board layout is as follows:

The board works well though the transistor gets hot, so do add a heat sink. The bare board etched at home using toner transfer looks like

and once populated it looks like this:

Pardon the messy tin, I'm trying to protect the copper layer from oxidizing away. Be careful when trying to run this for the first time. Most likely you'll short circuit the power supply :) The driver is very sensitive to the position of the POTS RV1 and RV2. Start with RV2 set so that R6 is connected to ground and set RV1 so that R3 is connected to ground. Then apply power to P3 (0-5V) and start increasing RV1. You can estimate the current that will be flowing even before you attach your dummy laser by measuring the voltage over C4 multiply that by two and assume 1V=1A. So if you read 125mV, you driver would output 250mA. The voltage at pin1 of the IC should be twice the voltage at pin 3 and equal to the voltage over R10 when a diode or dummy load is present.

1 x Transistor 2SD1758TLR
3 x Diodes 1N4148WS
1 x Dual opamp LM358MX
2 x 10k Trim pots PVG5A103C03R00
1 x 1 Watt 2512 SMD 1 Ohm transistor
1 x 100uF capacitor
1 x 100nF SMD805 ceramic capacitors
7 x 10k SMD805 resistors
2 x 1k SMD805 resistor
2 x 470pF 805 SMD ceramic capacitors (optional)

Sunday, April 24, 2011

1 Watt laser preparations

How nice to have an quiet Sunday working on your hobby in the garage. I spent the day preparing the CNC for the new laser diode that is coming this week. I'm getting a 1 Watt 445nm laser diode! For this purpose I thought it time to close up the CNC so no light shoots around and gets me or any of the kids ;-) and yes I do have the proper goggles as well, OD7+ for this wavelength. Don't even think to run that diode at it's full power without that. Be smart.

I've engraved the enclosing with the laser itself. The header of the blog is actually a shot of the case. Not bad looking :) I created that G-Code with truetype-tracer. This delivers some smooth looking fonts and allows for 'filling' Note that the filling requires you to turn off block-delete in EMC otherwise it will not fill. I've wasted a good amount of time trying to figure that out.

I've been trying to get the laser to cut stencils in some overhead sheets that I bought, but so far I've not been happy with the results. The TQFP32 footprint is tiny and the plastic melts too much. I still have a lot of parameters to tweak so it's a work in progress.

I seem to have broken the home switch on the y-axis. I'll have to look at the printer carcasses I have sitting in the corner for any more switches.

Tuesday, April 19, 2011

Laser530 paper stencil cutting

I finally received the BDR-S06J sleds and extracted the diodes from them. These diodes emit light at a wavelength of 405nm and go up to at least 500mA, where they put out about 600mWatts of power! That's not bad.

To drive these I needed a new driver. I was going to go with the FlexModP3 but after waiting for several weeks for my order I ended up building my own. I built a driver based on the StanHam design. I added a beefier output transistor and SMT components that I could source. I'll talk about this more in a future post.

To show off the new laser wrote a short script that parses a gerber file from Kicad and produces a g-code file for EMC. This allows me to create a stencil for SMT work at the office. The result in paper was quite good!

I'll need to find a suitable material to cut, Mylar is the way to go apparently. I'm hoping that overhead projector sheets will work.