Right away we saw an additional difficulty: the laser power needed to sensitize the dry-film generated an excess of light halo surrounding the main laser beam and exposing the tracks surroundings. There was no way to fix it. If we reduced laser power the halo disappears but we couldn't sensitize the dry-film. We were close of abandoning the project.
We have no idea of optics and we didn't want to modify the pickup, nor of course change their lenses. Inspired on a sunny day, we though we would install sunglasses on the pickup and filter out the excess of light. We tried with some kind of sunglasses and it works, but how would install them in the pickup and at the correct distance?
In addition sunglasses are expensive and this solution broke several of our design rules: low-cost, not tier-down, easy to do, etc. Finally, we found a better solution: solar film. Solar film is this kind of sun protective film used in home and car windows to filter UV light. It is very cheap and it's sold with different degrees of UV filtering so we tried with one semi-transparent mirror-style and it worked.
The film is self-adhesive and we simply pasted it on the printer bed glass. It is cheap and meets all the requirements. It also protects the PCB from ambient light. Actually we paste the solar film directly on the PCB, but probably it is possible to use other methods: glue it on a thin glass or just paint the glass with blue paint which filter some UV light.
At this stage we could sensitize the dry-film with good quality but still focusing manually so we boarded the development of the auto-focus algorithm. Our goal was read that signal, interpret it and move the lens to the appropriate focus point. But, once more time, it won't be so simple. While sniffing the FE signal with the oscilloscope we saw a lot of back noise.
We try moving a DVD disc in front of the pickup and we appreciated once in a while a very fast sinusoid wave. At that moment we didn't know it was the famous S-curve. For some reason that we unknown, the photodiode array get excited only when there is a variation on the disk distance.
In other words: we must move the pickup lens up and down to trigger the wave. Reading some CD's manuals we understood how it works. To implement this algorithm in the Arduino, we filter the back noise and sample the signal with an analogue port. Then we analyze the signal in real time, while we moved the lens up and down with another thread, until we detect the S-Curve and found the focus point.
We empirically measured the laser beam spot and it is approx. Main problems we had with Pickup Driver first prototypes were produced by electric noise. The FE signal we obtain from the pickup with the S-curve is very sensitive to that noise and it's difficult to find the focus point if the curve is hide into it. When we developed TwinTeeth, w e re-designed the circuit and we put on the same PCB some components which were isolated before: some in the own driver and some in the Arduino UNO shield.
But in the new circuit the focus lens Mosfet driver were in the same PCB that the rest of circuitry. This driver generated a lot of electric noise because is controlled by PWM. And the worst: it inducted the noise in the FE signal we use to detect the S-Curve and focus the laser. So we re-designed again the circuit in order to split it in two parts and isolated digital and analogue circuits on different PCB areas.
Also we isolated connector pins and decouple everything with some tantalum capacitors which are more suitable to the range of frequencies we were treating. We also included a choke to filter well the power suply noisy frequencies. We made and tested the new circuit and it worked fine, even better than the DiyouPCB prototype. The isolation of the analogue and digital circuits produced a free-of-noise FE signal which allow us to focus fine and which more accuracy than in previous versions.
Then we ordered some PCBs to a professional manufacturer because we wanted to test if the circuit still works while reducing traces, clearances, vias and sizing. Usually the quality of this kind of services is far away from the quality we can obtain at home.
This PCB and circuit is the last version we are using V3. When we developed TwinTeeth we wanted to seize the opportunity and improve the focusing system we had used for DiyouPCB. DiyouPCB used the UV laser diode to focus in one corner of the printer where we put some reflective foil. But we saw during testing that it was not enough robust because small variations on the PCB surface could affect the laser focusing.
TwinTeeth uses a smaller printing platform than DiyouPCB, so the first idea was to focus the laser on four reflecting focus points glued under a glass over the PCB. The robot automatically moved the toolhead to those focus points and took four focus measures. Then it used them to extrapolate the data to the rest of the PCB so it can accurately focus the laser while rastering the PCB picture. But we had some problems with the glass thickness. We were using an inadequate 2mm glass and we had to change to 1.
But even with the new glass we were not satisfied because the focus points were too far from the PCB corners so the measures were not accurate. If we wanted to improve the focus accuracy we had to focus on the PCB corners. This is not a problem because the PCB is reflective enough to focus directly on it but, as always happens, appeared two secondary effects: first we blurred the dry-film because the UV laser sensitizes it on the places it focused; second we had to focus through the glass and the solar film.
The filter was good while we printing but diminish performance when we focusing. So we were again in a dead-end alley. The PHRT is fantastic. The reason why we use the glass when using the laser toolhead is really because we need to glue this film on something. It was easy to turn the red laser on but unfortunately the red diode needs less current than the blue and when we turned it on it auto-destroyed. It happened three times till we deducted the problem, so we killed three more pickups during this testing.
Finally we limited the current of the red laser diode with a resistor. But once again we were not lucky enough: the S-curve we observed at the oscilloscope was very small. So we were decreasing the resistor in order to increase the current and obtain better S-Curve amplitude. But at some level the diode destroyed itself again. We were almost to throw in the towel when we did a quick test with the infrared diode.
We had a few pickups with the red diode burned but the infrared diodes seem still alive. That made us though that some pickup pin had to have the function of change from one photodiode pattern to the other. And so it was. If not used this pin, infrared diode turns on but no wave is obtained while focusing. We slightly modified the driver circuit and finally we are able to focus with the infrared diode.
The good news were that limiting the current with a 60Ohm resistor it seems it did not destroy itself. We did extensive testing with this version and the printing quality was good. We took some pictures with a 20x microscope. It was November when Dr. That document contained the last information we needed to reveal all the secrets of the PHRT and solved all of our doubts and confirmed some of our researches.
Then it extrapolate the focus data obtained to all the PCB surface and use it to maintain the lens focused while printing. It doesn't blur the film because the IR light does not affect the film and as the laser is perfectly focused we can print circuits at DPI which is similar quality does commercial paper printers have.
During the project we received some emails of people asking us why so obstinacy to use a blu-ray pickup instead of a nm laser pointer. The reason is because using the pickup we have a lot of benefits. It can focus automatically with precision and has a very small focal length , only of a few millimetres.
This allows to print with an accuracy impossible to achieve using a laser pointer. These laser pointers have a min focal distance of approx mm and you have to focus them by hand without any precision and reference. Instead, the pickup slips just a few millimetres from the surface of the PCB and the auto-focus system adjusts the laser to the small variations on the platform. On the other hand a short focal length means that the pickup is more secure: not dangerous if you follows basic laser safety rules , even unenclosed.
Laser pointers are really dangerous because has a poweful long-range laser. There is a lot of undiscovered pickup functionality yet. I hope our project had inspired some people to research more pins and end our job. For us it is enough as we covered our goals and we will continue with our project: the PCB mini-factory.
You are here Home. Hacking the PHRT. We called it DiyouPCB But unfortunately the mechanics and timing belts produced mechanical vibrations affecting the laser beam. TwinTeeth So we started again from scratch with new designing criteria: reduce vibrations and resonances. A photodiode array which receive the RF signal and help focusing on. If we see the picture on Sam's page, the laser operation is relatively simple: The laser diode 2 emits UV light that is conducted through a system of mirrors and prisms until the focus lens This lens can be moved in several axis using three coils.
This allows the pickup to focus the laser on the disk, follow the audio track tracking and correct the laser angle. Been around 10 years. Bet it's put quite a few smiles on quite a few people. Including me. Last edited: Jul 20, Lifetime17 Well-known member. Joined Dec 15, Messages 6, Points Hi Hak, Yes it seems like it came a long way and still is going strong. Nice reading a little laser diode history.
CynicalBrad Well-known member. Joined Sep 4, Messages Points I recall harvesting a few of these. A phrt "build" was even my first laser. Good times. Joined Oct 14, Messages 6, Points Joined Sep 20, Messages 19, Points Yeah, that poor little diode doesn't seem to get much use any longer.
Not since the X12 and X16 guys came around. I guess in LD terms, 10 years is a lifetime. Now, blow out the candles. Last edited: Jul 21, Wright is a photog who maybe had an Xray tech day job and got into doing Xray art. The pic of the Chambered Nautalis is quite interesting. GL getting the pics to load.. The artists work has been featured in several magazines and publications, for non-profit organizations. Please proceed to the galleries for a breathtaking look at this transparent world.
Joined Sep 20, Messages 17, Points Man time flies I must be a hoarder Joined Feb 22, Messages 9, Points Click to expand BUT still a great read.. Benm Well-known member. Joined Aug 16, Messages 8, Points RB astro Super Moderator.
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The PHRT incorporates a UV laser diode on the nm wavelength. The spectrum and power is more than enough to sensitize UV film even resin. The PHRT was designed to read HD-DVDs so can focus a beam to far below mm. They got autofocus working with the UV laser, but couldn't. Laser lens for Xbox console. - Compatible with Microsoft Xbox