I just meant using tech built for software defined radio to look at analog signal coming out of detectors as opposed to e.g. letting software and electronics in a DVD drive process the signal as in the examples above with disc-based bioassays.
OK. I had forgotten about those posts. I was excited about the possibility of AFM and alternative applications thereof. Iâm still not quite sure why you canât use something simpler to read an ELISA with an enzymatic amplification in the reporter. Possibly I should read that ELISA paper. How are you going anyway? Are you back in Berlin? Iâve just been locked down again in Melbourne.
You are right! The spinning disc does provide high linear speed. The AFM application is limited by the raster scanning speed. I really amazed by your knowledge about the ICs 
Here some more links on the OpenAFM / LEOG2NANO
I will be in Berlin for the week of August 13th 2020 and talked with @bengtsjolen about meeting and doing a hack session on laser scanning / optical pickups / ReSeq / spectrometry
I can bring spectrometer / deuterium lamp / DVD laser scanner / PHT OPU
Who would be interested and can join (physically or remotely)?
Where and when should it happen?
Urs
@gaudi, I could potentially be interested in doing something remotely. Or at least following what youâre up to.
John
@jmarkham super if you can work on the topic remotely. And I am sure we can link you in somehow.
I booked Berlin from Sunday August 9th to Saturday August 15th. @bengtsjolen you think we can work in your lab/studio/apartment or what would be a good place to set up a temporary lab? There is also TopLab that I have never visited. And I spent some nice time with @wolfgangspahn on Randen and would like to visit his space if possible.
Urs
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@gaudi
I am trying to make the DVD laser Scanner microscope (v2) but have some doubts regarding the schematics shown on the GitHub page compared to the one shown in the Gaudi labs official page for DVD laser Scanner Microscope.
This is the design rendered from the gerber (pcb) files from the Github page
This is the circuit shown on the Gaudi labs website (Under Second prototype of DVD laser scanner)
If we see clearly, there are different( additional connector are available on the design on website( purple PCB ) which is not present on the pcb deisgn.
Can anyone help me out regarding this.
I hope that we can discuss a bit about it.
Hi
There are two separate designs here, one for the PHR803t, which is in the Github and in fact you connect the PHR803t with a flat cable and another connect through the 3 pins T1,F1 and REF the second. You connect the opu as shown below:
The image of Gaudi labs website is another SF-HF65 OPU. Which is a DVD driver.
I recommend you use PHR 803 because the blue laser gives you a higher resolution.
Below is a schematic of both circuits designed by Urs.
DVDLaserScanner.pdf (114.6 KB) dvdschem1URS.pdf (232.0 KB)
Best,
Mojtaba
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Hi all, happy to see the activity around DVD Laser Scanner. I just updated the GitHub repo, finally fixed the error on U9 / U13 and updated the BOM. This is now the latest version. Pictures on the website need to be updated. Everything still quite rough as this was more of an experimental project.
Here at Anyma hack-week, I started experimenting with â3D printingâ with the DVD Laser Scanner by exposing a small piece of glass coated with photo sensitive polymer. And it seems to cure it in a pattern. To be continued.
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Hey Guys
I am new to the forum, and I wanted to find an open source afm. It seems that you guys are stuck. I am just curious where? I thought the hardest part would be creating the opu driver. After, you can utilize piezo materials to create the required xyz movements. From there, you create a program that tries to keep the FES signal at zero. When the tip deflects due to a change in height, you would see a change in the FES signal, and try to adjust it back to zero using the piezo z axis. You can calculate the delta z at the point? Sorry, I do not mean to oversimplify everything ,I know the rest is still hard and I know I am missing something.
Mojtaba, I am attempting to fabricate the same circuit in this image. I have contacted a few circuit fabricators who have told me that the BOMs found on the GitHub are missing many part numbers. Who did you contact to have your circuit created?
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Dear all,
Here is an opportunity for people who like to hack and make use of the optical pick-up units
https://www.nature.com/naturecareers/job/postdoc-in-rapid-clinical-assessment-of-skin-barrier-function-by-corneocytes-nanotexture-technical-university-of-denmark-dtu-735324
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Just a quick shoutout and congrats to Gaudi that his scanner was recently featured on Hackaday: DVD Optics Power This Scanning Laser Microscope | Hackaday
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a friend documented this own DVD laser scope variant here: DVD-Drive based Laser Scanning Microscope [Lötlabor Jena]
checkout the integrated motor and laser diode driver chip he found, TI TPIC2050, very cheap and effective
4 Likes
https://www.nature.com/articles/s42005-021-00532-4
Hacking OPU and invading 3D printing fieldâŠ
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Hi
I used Gerber files to build this board. Because companies close to us needed the Altium file.
Of course, in the version I used, the pins related to ground and voltage were the opposite. I turned the ]Cs upside down and got the answer.
Hi,
I am theoretical physics student currently located in Brazil and recently got my hands on some SF-HD65 units in order to start my journey in the OPU world with a well-documented unit, as a weekend/quarantine project!
I succeeded to drive the VCMs and the 650nm laser diode as expected.
For now, I am using an ADS1118 16-bit ADC with programmable amplifier in order to read out the signal from the PDIC. With a small mirror or coin I receive a signal back, however, of relatively small intensity. (Roughly 10mV p-p at the a-d pins and roughly 40mV p-p at the RF signal pin.) This wouldnât necessarily be a problem, however, I am observing non-negligible drifting of the background signal of the PDIC pins! Roughly 2mV at the a-d pins and multiple 10mV at the RF pin! (I am using a driving circuit similar to the one from the datasheet and have a well-buffered 2.1V reference voltage source in place.)
Is this behaviour expected or am I doing something very seriously wrong? What should I do about it?
Another matter is that the laser output seems to be very low at around 90mA load when compared to the optical output power of laser diodes that I harvested from other DVD-RW drives. For a Laser Scanning Microscope would a higher laser output power be useful or do we need to limit the optical output power nonetheless, in order not to damage the samples?
Ok, my laser output power seems to have been the issue!
I am now using yet another of my testing unities SF-HD65 (after having tried two so far) and the driving circuit now reaches only 40mA direct current with realistic optical output power! The PDIC pins a-d now return voltages of around 0.5V p-p.
Problem solved.
Next question. What is the advantage of using an opamp to further amplify the signal instead of using the ADC that I am using, if any? (The samplerate of the ADS1118 is relatively low, up to 860SPS, but likely we would not need to go beyond that limit would we? As alternative I have the 8-channel 12-bit ADC MCP3208 in mind with much higher samplerate.)
Based on the SF-HD65 pickup units, I proceeded to carry out some first scans. Among other test samples, I used a DVD-R and a CD-R. The image below is taken of a written CD-R using the RF-Signal. As we can see, I do not succeed to resolve the pits of the CD yet. (Taken with the 650nm laser though.)
What could be possible causes of the distortions? Some things that came to my mind:
- Vibrations of the surface
- Hysteresis of the VCMs
- Long settling time / damped oscillation of the VCMs
- Input voltage variations at the power opamps that supply current to the VCMs
Note that I have not taken any further measures to stabilize the 5V input voltage. I used a mere protoboard voltage regulator as reference voltage for the DACs and ADCs. Does it make sense to use more sophisticated 4.096V and 2.048V voltage references while continuing to rely on a mere L7805 as input voltage regulator?
I also have some doubts about which is the main parameter that limits the speed of a scan.
Theoretically, the inductance L of 9”H (± 6”H) of the tracking actuator at a resistance R of 3.7Ω (±1.1Ω) alone yields a time-constant of L/R = 2.4 ms (in worst-case 5.8 ms). Knowing that in order for the current through the coil to approach the new stable equilibrium we should wait at least 3 to 5 time constants, a time per pixel of less than 10 ms seems unfeasible? That leaves aside the dynamical considerations of the spring constant of the actuator as well as the inertia of the lens mounting.
Some of you can share their experiences with me? 
Lars