I wanted to make sure Alex's system of Diode laser + laser controller + optical splitter was working fine and then make a manual measurement for AS55 PD. Manasa was supervising my work and helping me with unhooking the fibers and taking power meter readings. I have tuned on the power to REF DET from under the POY table.
I switched on the laser sitting in the 1Y1 rack and turned up the driving current to 240mA. On checking the laser power readings at AS55 (AS table) and REF DET (POY table) simultaneously, we got readings of 1.6mA and 2.4mA respectively. This much difference in readings was not expected and I did not continue taking the readings for transimpedence measurement.
I will rectify if this unequal splitting of power by the 1x16 optical splitter is going to cause any difficulties for the automated PDFR system measurement technique and resolve it if needed.
I finally did carry out a measurement on the network analyzer. This proves that the previous system will work properly. Just the optical splitter problem is to be taken care of.
For this, after Elog 10102, I did not touch any of the tables or photodiodes. Only turned on the laser at 1Y1 and took readings from the NA located nearby. I switched off the laser after measurements. The power to REF PD remains on.
I plotted transimpedence plots in the usual way and got ridiculous values of 15 ohms at 55MHz. Obviously there is the problem of varying amount of power illuminating the REF PD and AS55.
So, I just plotted the bode plots of transfer function got from the NA to check if the characteristics of AS55 looks as it was supposed to be and Yes! I got a nice peak at 55MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
2) Number of Points sampled in the range: 801
3) Type of sweep: Linear
The experimental values obtained were:
The experimental values obtained were:
DC output voltage of REF PD: 7.48V
DC output voltage of AS55: 53.7mV
Power incident on REF PD and AS55 respectively: 2.4mW and 1.6mW
Taking the DC transimpedence of AS55 as 66.2 ohms (from schematic given at D1300586-v1) and for REF PD as 1E04 ohms
Hence, Responsivity for REF PD and AS55 respectively are: 0.312 A/W and 0.51 A/W
The data and code used are in the zip file.
The updated script for remotely getting data from Agilent 4395A network analyzer is located at /users/nichin
This network analyzer device is located at crocetta.martian (192.168.113.108)
> python NWAG4395A_modified.py [filename.yml]
I connected a simple 2MHz Low pass filter between the modulation output and signal input of the NA and ran a scan from 0Hz to 20MHz. The script was run from Chiara.
The expected plot was obtained and is attached here.
I now have to work on setting up the RF switch in rack 1Y1 to select between required PDs and also on the code that chooses which channel is being selected.
There is also a problem of 2 8x1 RF switches being present, instead of one 16x1. Alex's code for RF switching does not take this into account.
Sorry Rana for not giving much attention to the plot. I will definitely change the way they are being plotted.
I was more focused on getting the data acquisition to work. Also, the current script gets only the magnitude and not the phase... I still have to work on that.
[Nichin, Eric Q]
We added a new LAN wire from Rack 1Y4 to 1Y1 to connect the RF switch at 1Y1 to the martian network. The wire is labelled "To RF Switch (1Y1)"
The wire was run along the Y arm in the tray right next to the vaccum chamber, not the one on top.
[ Nichin, Eric G]
RF cables have been installed between deomodulator output PD RF MON and the RF switch for the following PDs:
REFL33, AS55, REFL55,REFL165,REFL11,POX11,POP22
The cables are labelled on both ends and have been run on the overhead tray.
The cabling looks neat on 1Y2, but not so much in 1Y1(RF switch). I will better organize them later.
There were quite a few more demodulator units labelled with PD names. Do any of them need to be included in the automated frequency response measurement system? Please let me know so that I can include them to the RF switch and check them for proper illumination, which i will do for all the above PDs next week.
I tested the RF switch selection code and then the data acquisition code for the NWAG4395A network analyzer and they both seemed to work fine. I selected the channel to which AS55 is hooked up to and then remotely got its transfer function.
There is quite some noise in the system as the plot shows. Especially the phase. Maybe my driving power was a bit too low. Have to figure out the reason behind this.
In the order that makes more sense to me, it looks like you have:
REFL11, REFL33, REFL55, REFL165,
We don't really need POP22 right now, although we do want the facility to do both POP22 and POP110 for when we (eventually) put in a better PD there. Also, we want cabling for POP55, so that we can illuminate it after we re-install it. If we're working on 2f PDs, we might as well consider AS110 also, although I don't know that there was a fiber layed for it. The big one that you're missing is POY11.
A new RF cable has been included for POY11. Cabling for POP55 and POP110 might or might not exist. I will check and report it.
The RF cables have been routed incorrectly. The cables run to the module from the front of the rack. We cannot close the doors to the racks if they are to remain this way.
I have asked Nichin to reroute the cables properly.
RF cables have been rerouted from the side of the rack, under the supervising eye of Manasa.
I moved the red ladder from near 1X4 to 1Y1 and back again.
Current list of RF cables:
I have not connected them to the RF switch yet. ( until I figure out how to get both the switches working properly)
The RF multiplexer is configured as shown in the figure. It is now effectively a 15x1 RF mux.
To select a required channel:
Run the script as shown below
>python rfMux.py ch11
For channel 10 to 16, you can just enter the required channel number and it is routed to the output.
For channel 1 to 8, you only need to input the required channel number as above. No need to run the code again to select ch9 after selecting ch1-8
How the NI-8100 controller works:
Whenever any channel of one switch is selected, the output of the other switch is set to its ch0 (ch1 and ch9 in the figure).
So selecting ch1-8 will automatically select ch9 as output for the other switch. IF you send a command to select ch9 afterwards, the first switch will be automatically set to ch1 and not stay on what you had selected before.
My plan for next week is...
1) 1) Taking DC output readings with multimeter for each PD to create a database for all the PDs. Requires taking off the table tops for each PD. Also, making sure each PD is illuminated properly.
2 - 3 Hours inside the lab
Requires presence of expert
Occupies all the PDs , RF switch and the Network analyzer.
2) 2) Integrate the switch selection script with the Network analyzer script to complete the automation part of the project. (If time permits, build a simple GUI for easy operation)
Occupies the control room computer, RF switch and the Network analyzer
3) 3) Create a database of canonical plots for each PD to compare with the current plot and maybe even plot the difference between the current plot and canonical plot.
Occupies the control room computer, PDs , RF switch and the Network analyzer.
4) 4) Fit the transfer function or transimpedance using vector fitting. (vectfit4.m)
5) 5) Update 40m-Wiki
6) 6) Progress Report to be submitted to SFP.
AIM: Taking DC output readings with multimeter for each PD to create a database (required for transimpedance calculations), by taking off the table tops. Also, making sure each PD is illuminated properly.
What we did:
REFL11: Pinc = 0.91 mW VDC = 34.9 mV
REFL33: Pinc = 0.83 mW VDC = 33.2 mV
REFL55: Pinc = 1.08 mW VDC = 42.7 mV
REFL165: Pinc = 0.79 mW VDC = 115.3 mV
AS55: Pinc = 0.78 mW VDC = 31.3 mV
POX11: Pinc = 0.83 mW VDC = 34.7 mV
POP22**: Pinc = 1.08 mW VDC = 5.82 mV
POY11: Not illuminated; there was no optical fiber mount. Although, there was a fiber near it with a cap on the end. It also looks like there is no space to put in a new mount near the PD.
REF PD: Pinc = 1.19 mW VDC = 8.2 V (REF PD = New focus 1611)
**Note: The current POP 22 PD does not have 2 different outputs for DC and RF signals. I unplugged the RF cable from the output, took readings with the multimeter and then plugged back the RF cable.
I will calculate the responsivity for each PD and compare it to the expected values.
The following values are going to be entered in the param_[PDname].yml file for each PD. I am elogging them for future reference.
I got the values from combing schematics and old Elog entries. Please let me know if you believe the values are different.
I have configured a NEW Prologix GPIB-Ethernet controller to use with HP8591E Spectrum analyzer that sits right next to the control room computers.
Static IP: 192.168.113.109
I have no clue how to give it a name like "something.martian" and to update the martian host table (Somebody please help!!)
I have no clue how to give it a name like "something.martian" and to update the martian host table (Somebody please help!!)
The instructions for adding a name to the martian DNS table are in the wiki page that I pointed you to:
The instructions at https://wiki-40m.ligo.caltech.edu/Martian_Host_Table are outdated!
The name server configuration is currently at /etc/bind/zones/martian.db [ source: elog:10067 ]
Anyway, I need superuser access to edit the files, which I don't have. Even if I did know the password, I don't think it's a good idea for me to be messing around. So any of the 40m folks please update the martian table to include:
The martian lookup tables are located at /etc/bind/zones/martian.db and etc/bind/zones/rev.113.168.192.in-addr.arpa
Jenne updated these to include santuzza.martian 192.168.113.109
The method to restart named server given at https://wiki-40m.ligo.caltech.edu/Martian_Host_Table also does not work.
I restarted it using >sudo /etc/init.d/bind9 restart
The named server is now updated and works fine. :) I will update the 40m wiki now.
Successfully completed the rudimentary GUI for PDFR system. (users/nichin/PDFR)
Pressing any of the buttons above runs the script that does the following:
1) Change RF mux channel to the required one.
2) Frequency sweep on the network analyzer. The common sweep parameters are in a file named param_NWAG4395A.yml . PD specific parameters are in param_[PD name].yml in their respective folders
3) The transimpedance is calculated and the plot is saved as PDF in the respective folder for the PD. Each set of measurement data and plot is in a timestamped subfolder.
To take transimpedance readings for each PD and create a canonical set of data that can be used to compare with data obtained for every measurement run.
I went into the lab and connected the RF cables to the Mux. Will take measurements for each PD henceforth.
The script for running continuous scans on HP 8591E spectrum analyzer is located at scripts/general/netgpibdata/HP8591E_contdScan.py
Give the file HP8591E_param.yml as an argument when running the script. This contains the sweep parameters: Start and stop frequencies along with the place where the plot is stored as a PDF.
The default PDF is located on the Desktop and is named HP8591E_View.pdf Open this using okular and then run the script. (Okular pdf viewer automatically reloads the PDF as and when a new one is created)
What the script does:
1) Set the start and stop frequencies as given in the .yml file
2) Take a data trace and plot it in a PDF.
3) Repeat taking traces and update the PDF. Untill Ctrl+C is pressed (PDF refresh rate: approximately every 3 seconds )
4) Exit smoothly after the keyboard interrupt.
This spectrum analyzer is connected to a GPIB - Ethernet controller that is configured as santuzza.martian (192.168.113.109)
I have currently stolen the wireless modem from the spectrum analyzer inside the lab (vanna.martian) and using it for this one. *poker face*
Get the plot to show where the two biggest peaks are located. Currently it recognizes only the biggest one.
Possibly have makers on the two peaks.
PFA a sample pdf
A test run was conducted on the PDFR system last afternoon and transimpedance plots were generated for 6 of the PDs. The laser was shut down after the test run.
I have not verified (yet) if the transimpedance values indicated by the plots are correct or not. The values mostly look INCORRECT. But the peaks are exactly where they need to be. *phew!*
Reasons: Incorrect calibration, Light other than from the PDFR system fibers on the PDs
Will have to work on debugging all this.
1) Debugging transimpedance calculations in the PDFR
Requires presence of an expert whenever I get inside the lab to take DC measurements or check the illuminating fibers.
2) Creating and incorporating canonical data plots with every measurement of PDFR.
3) Transfer function fitting for transimpedance
4) Improve the Spectrum analyzer scan scripts as mentioned in my elog.
Updated script does the following:
1) Gets the highest 2 peaks
2) Puts a marker on the peaks. Now it looks very similar to the spectrum analyzer display.
3) The refresh rate is still 3 seconds. It might become better if the analyzer was hooked up to a wired martian LAN port rather than the wireless module I am using now.
PFA a sample pdf
In a attempt to debug the values of transimpedance generated by the PDFR system, I did a manual measurement for REFL11 PD.
Pinc = 1.12 mW T_dc = 10000 V/A (datasheet)
Vdc = 7.68 V T_rf = 700 V/A (datasheet)
Calculated Responsivity = 0.68 A/W (Which matches perfectly with the datasheet value of 0.68 A/W)
Pinc = 0.87 mV T_dc = 66.2 V/A (schematic)
Vdc = 32.5 mV
Calculated Responsivity = 0.56 A/W
Network analyzer reading at 11 MHz : 0.42
Calculated RF Transimpedance = 460 V/A
40m Wiki : RF Transimpedance = 4 kV/A
I ran the same measurement using PDFR system and got the same results.
Attached: the automatic data and plot obtained.
Conclusion: The PDFR system and manual measurements agree with each other. However the values do not match with 40m Wiki. I have no clue about which measurement is correct or any mistakes I might be making in the calculations.
Rack 1Y2, I took transfer function measurements for each of the following demodulator boards: REFL11, REFL33, REFL55, REFL165, AS55, POP22, POX11 and POY11.
What I did:
1) Removed the wire at PD Input to demodulator board.
2) Put the MOD output from network analyzer into PD input of board.
3) Ran a sweep from 100kHz to 100MHz.
4) Measured the transfer function between PD RF MON and PD Input. (The PD RF MON signal came out of the RF multiplexer, so the mux is included as well )
5) Put the original wire back at PD Input.
The plots clearly show an attenuation of 20dB (factor of 10) for all the demodulator boards. This explains why my transimpedance measurements are off by 10 times.
Note: for REFL 165, there was an extra 100MHz high pass filter installed at PD Input. I did not remove this and made my measurements along with this.
a) Modify the PDFR system to calibrate out this attenuation.
b) Measure the transfer function between the input and output of RF mux, so that we can have just the transfer function between PD input an PD RF MON (for documentation's sake)
I repeated the exact steps above and made sure everything was back where it should be after I was done.
Reason I had to retake the measurements:
My script for acquiring data from the AG4395A network analyzer was such that it first acquired the magnitude data from channel 1 and then recorded phase data from channel 2 without holding its trace. Hence the phase and magnitude data were not exactly in sync with each other. So, when I tried to fit the data to a model using vector fitting, I ended up with very bad results.
I have now changed every single script relating to the network analyzer to just get the real and imaginary data in one go and then calculate the phase using this data.
The fitting process is now in progress and results will be up shortly.
Does not require time from a lab expert.
The plots in the previous Elog includes delay and a little attenuation by RF cables and the RF mux.
Today I separately calculated the delay and attenuation for an RG405 cable (550 cm) and the RF mux(using really small RF cables). These delays should be accounted for when fitting the transfer function of Demodulator boards and transimpedance of PDs.
The plots are in both semilogx and linear.
A time delay can be modeled as the exponential transfer function : e(-sTd) as seen HERE . Therefore the slope of the phase gives us the time delay.
A RG405 coaxial cable, exactly 5.5 meters in length, was fit to an ideal delay function e(-sTd) , with Td = 150 ns.
The plots shows the actual data, fit data and data after correction using the ideal model stated above.
Delay in RG405 cables is approximately 27.27 ns per meter. This value can be used to correct the phase in measurements of transimpedance for each PD by dividing out the ideal transfer function for time delay.
[EDIT: This looks like we have about 12 % the speed of light inside the RF cables. Too small to be true. I will check tomorrow if the Network analyzer itself has some delay and update this value.]
The varying attenuation of about 1dB due to the cable is not compensated by this. We need to separately include this.
Things to do:
1) Get the length of RF cables that is being used by each PD, so that the compensation can be made.
2) Calculate the attenuation and delay caused by RF multiplexer and Demodulator boards. Include these in the correction factor for transimpedance measurements.
A time delay can be modeled as the exponential transfer function : e(-sTd) as seen HERE . Therefore the slope of the phase gives us the time delay.
The transfer function of RF multiplexer in rack 1Y1 (NI PXI-2547) was fit to an ideal delay function e(-sTd) , with Td = 59 ns.
Delay the RF Multiplexer is approximately 59 ns. This value can be used to correct the phase in measurements of transimpedance for each PD by dividing out the ideal transfer function for time delay.
I used vector fitting to fit the transfer functions between RF input and PD RF MON of demodulator boards. These fittings can certainly do a lot better on LISO, but for the time being I will assume these to be good enough and change the main PDFR scripts to calibrate out this factor and get a decent reading of PD transimpedance. Then it will just be a matter of changing the transfer function parameters. A lot of work needs to be done on the PDFR interface and plot features.
Attached: The plots showing data and fits.
The PDFR system's interface and scripts have been updated to include quite a few more features.
On the interface side, there are buttons to open the previous plot for each PD and also a single button to run the scans on all PDs sequentially. The previous plot buttons actually open a softlink that is updated each time a measurement is taken.
Running a scan now pops up a terminal window to show messages that help understand whats going on.
In the background, the script now takes in the transfer function of the demodulator board in ZPK format and calibrates it out of each measurement. The parameters are given .dat files making it easier to replace the transfer function. (Remember my last elog which showed that the fitting of transfer functions were not really great and that I am going to use it anyway to get the script updated.) Also, the script now takes the delay in the RF cables and calibrates out that as well. So we no longer have the huge phase variations and the phase related to transimpedance are visible.
A test run was conducted today. Plots attached.
NOTE: The test can be conducted only on REFL 11,33,55,165 , AS55, and POX11.
POY11 has an optical fiber routed from this system, but there is no space to actually illuminate this PD. So it is currently not included in our system, even though there is a button for this.
POP22 has a fiber illuminating it, but its a unknown broadband PD. I do not know it's DC transimpedance or other values. Its just of matter of updating a few files that feed it's parameters into PDFR.
However, for the above PDs, the demodulator boards have been fit to a transfer function and the script is ready to go as soon as the above problems are fixed.
Conclusion: The plots look noisy. But, the transimpedance now resembles the one on 40-m wiki for all the PDs, both the shape and values.
There will be some errors that are induced because of improper demodulator TF fitting. This has to be taken care of eventually.
Work remaining: Create a canonical set of plots for each PD and set them as the baseline. These canonical plots will be plotted along with each measurement for easy comparison.
A well documented manual for the whole system clearly explaining where and how it takes all the parameters into account so that anybody can easy update just the essential information.
The Transimpedance plots of PDFR now have a reference plot or baseline plot along with the current measurement, for easy comparision.
Current Work: Getting Matlab's vectfit3 to work simultaneously on the transimpedance readings and print the zeros and poles alongside the plots.
The PDFR system now has the capability to automatically run vectfit3.mat using a wrapper script named vectorfitzpk.m
This is done via a shell script being called from inside python that inturn runs the matlab script.
1)The PDFR scripts have all been migrated into /scripts/PDFR/
2) The MEDM screen to run PDFR is /medm/MISC/PDFR.adl
3) A new button has been added on sitemap to open the above medm window.
4) All data and plots generated will sit in /scripts/PDFR/"PD Name"/
5) All features are working after the migration and absolute file paths are being used.
Work Remaining : Manual for others to make changes and keep using my system.
The PDFR system has been documented in the 40m wiki and all the relevant information about making changes and keeping it updated have been mentioned.
This pretty much wraps up my SURF 2014 project at the 40m lab.
Here is my work plan for this week:
1) Help Steve clean small table for experiment
2) Remove aluminum base from TT suspension
3) Mount shaker onto table base
4) Mount horizontal slider onto table base
5) Connect TT suspension, shaker, and horizontal slider
1) Begin building circuit for displacement photosensors
2) Calibrate photosensor using linear regions of power versus distance curves
3) Circuit box for photosensors?
The small optical bench (next to the MC-2 Chamber and the tool box tower) has been cleared of the misc. object previously on it, cleaned, and leveled (after much calibration X___X).
PLEASE, PLEASE, PLEASE do NOT MOVE OR HIT THE TABLE! It was incredibly painful to level.
This is how leveling the table made me feel...
VERY SAD...so do not move please!
The shaker has already been moved to the table and the amplifier for my shaking experiment is located behind the table (not on the table, as to prevent scratching).
I have made my transfer function model and posted it to the suspension wiki. Here is the link to my model!
Bode Plot Model
Please let me know if there need to be any adjustments, but I have posted the bode plots, a model image, and an explanation of why I think it's right! ^ ___^ V
I am currently working on the photo sensor circuit for the displacement detector. So far, I have gotten the infared LED to light up! ^ ___^ V
I am now trying to get a plot of forward voltage versus current for the LED. HOPEFULLY it will match the curve provided in the LED datasheet.
I'm using the bread board circuit box and when I'm not working at the bench, I have signs posted. PLEASE DO NOT REMOVE THE CONNECTIONS! It is
fine to move the bread board circuit box, but please do not disturb the connections > ____<
Here is a photo of the workspace
NOTE: The potentiometers on the bread board circuit box (the one I have been using with the signal generator, DC power, LED displays, and pulse switches) is BROKEN!
The potential across terminals 1 and 2 (also 2&3) fluctuates wildly and there dial does not affect the potential for the second potentiometer (the one with terminals 4, 5, and 6).
This has been confirmed by Koji and Jaimie. PS I didn't break it! >____<
NEVERTHELESS, using individual resistors and the 500 ohm trim resistor, I have managed to get the current versus forward voltage plot for the Hamamatsu L9337 Infared LED
I have updated the TT suspension wiki to include a new page on my transfer function model. In this new page, an introduction and analysis of my transfer function (including a comparison of the transfer functions for a flexibly- and rigidly-supported damper) are included. This page contains linear and logarithmic bode plots. Here is a link to the transfer function page.
I have also updated my photosensor page on the TT suspension wiki so that the experimental data points in my current versus voltage plot are plotted against the curve provided by the Hamamtsu data sheet. I have also included an introduction and analysis for my mini-experiment with the forward voltage and forward current of the LED. Here is link to the photsosensor page.
Today Ishwita, Sonali, and I completed basic laser safety training with Peter King. I completed the Laser Safety Quiz and have turned in my certificate sheet.
I just need to turn in a signed copy of the Lab Safety Checklist to SFP (which I can now have signed by Koji after completing the course).
Steve and I have removed the TT mirror from the clean box. It is now on the small optical table in the lab that I have been working on. Thanks to Steve, all of the mechanical components for the horizontal displacement measurement experiment are compiled and on the small optical table. Here is a photo of the small optical table with the gathered components.
The plan is to attach the slider and the shaker directly to the black mounting plate. On the slider, we we then place the smaller black mounting plate (with the lip). The lip will attach to the shaker. We know exactly where to drill and everything is lined up. The shaker will be placed on the smaller black mounting plate (with the lip). The assembly will begin on Monday.
Here is a photo of the planned set-up for the shaker and the horizontal slider + mounting base.
Update of Week 3 Work:
-I've finished reading The Art of Electronics Ch 1, 2, and 4.
-The mechanical stage for the horizontal displacement measurements is set up.
-I've opened up the circuit box for the quad photodiode and am currently working on the circuit diagram for the box and for the quad photodiode sensors.
Later this week, I plan to finish the circuit diagrams and figure out how the circuits work with the four inputs. I also plan to start working on my first
I have finished drawing the circuit diagrams for the quad photodiode boxes. Here are copies of the circuit diagram.
There are three main operation circuits in the quad photdiode box: a summing circuit (summing the contributions from the four inputs),
a Y output circuit (taking the difference between the input sums 3+2 and 1+4), and an X output circuit (taking the difference between the
input sums 3+4 and 1+2). I will complete an mini report on my examination and conclusions of the QPD circuit for the suspension wiki tomorrow.
In order to test this preliminary circuit, I need to build the photosensor heads. Yesterday, Suresh helped me to open one of the professionally-build photosensors in the lab to understand how to arrange my photosensor heads. I now understand that I need to rigidly-mount the PCB to photosensor head box. I plan to use the PCB below. It will be sufficient for the lower-frequency range (below 10Hz) that I am interested in.
I would like to use a metal box like the one below to make each photosensor head. I looked in the lab last night for similar boxes but could not find one. Does anyone know where I can find a similar metal box?
I am now working on accelerometer. I am working on attaching these metal wires to the pins of the accelerometer so that I can use clip leads to power and extract voltage measurements from my circuit.
Today I tested the photosensor head combination (2 Hamamatsu S5971 photodiodes and 1 Hamamatsu L9337 LED). I discovered that I had burnt out the LED and the photodiodes when I soldered them to the PCB board.
After looking up soldering information on Hamamatsu photodiodes, I learned that I need to solder at least 2 mm away from the head. I checked the pins of my burnt-out photodiodes and I had soldered 1.5 mm away from the head. To prevent this problem from happening again, Suresh suggested that I clip a lead onto photodiode/LED pin while I solder on connections to help dissipate some of the heat.
Today I was able to get a single photodiode (not attached to the PCB) to measure light emitted from an LED and I observed how voltage fluctuated as I moved the photodiode around the LED.
Suresh and Jamie also helped me to fix my photosensor head design (to make it more electrically-stable). Originally, I had planned to solder the LED and photodiodes onto a PCB and to mount that PCB to the front of a small metal Pomona Electronics box (with a whole cut out for the photodiodes and LED) using spacers, screws, and nuts. However, the PCB I am using to solder on the LED and photodiodes has metal connections that may cause problems for the LED and photodiodes lying on the surface. Now, the plan is to have the LED and photodiodes mounted to the PCB with an insulatory PCB in between. Below is an explanatory picture. I will determine the placement of the LED and photodiodes after making screws holes in the two PCBs to attach to the metal face of the box. I want to attach the screw holes first to make sure that the PCBs (and attached photosensor) are centered.
Ah! I see! Thank you!
I should put the LEDs and photodiodes closer together so that more of the reflected light falls on the photodiodes and the photodiodes have a higher response.
Also the reflectivity of the mirror will be optimized if the incident light is normal to the mirror surface. We will be setting up the photosensor and mirror so that the LEDs
emit light normal to the mirror surface. During displacement, this light may be slightly off-normal but still close to normal incidence. We want the photodiodes to be close to the LED since we want
them to detect light that is close to the path of normal incidence (small angles of reflection). [Thanks to Jenne for helping me figure this one out!]
Thank you for the suggestion ^___^
You are right Jamie! Thank you for the correction! I will now use the Teflon sheet instead of the PCB piece.
The photodiodes do have three legs, but I imagined the third one lying on a different plane, since it is spaced apart from the two I have drawn.
I should include this third leg in my drawing?
Today I learned some important circuit-building lessons while testing my photosensor circuit box (i.e. how NOT to test a circuit and, conversely, things that should be done instead).
I blew my first circuit today. The victim is in the photo below (bottom 7805 voltage regulator). The plastic covering fell off after I removed the fried regulator. After checking various components, I figured out that I blew the circuit because I had forgotten to ground the regulator. Although this was very unfortunate, I did make an important discovery. While testing the voltage output of the 7805 voltage regulator (I put a new one), I discovered that contrary to the claims of the datasheet, an input voltage of 5V will not produce a steady 5V supply. I found that at 5V, my regulator was only producing 4.117 V. I was using a 5 V supply because I wanted to use only 1 power supply (I was using a two-channel power supply that had a fixed 5V output to produce the +15, -15, ground, and 5 V I need for my photosensor circuit box). After seeing this, I got a second power supply and am now using 10V to as an input for the regulator to produce 4.961V. I found that from a voltage range of 10V to 15 V, the regulator produced a steady 4.961 V supply. I have decided to use 10V as an input. My newly-grounded voltage regulator did not smoke or get hot at 10V.
After several more debugging trials (my LED was still not lighting up, according to the infared viewer), I learned another painful lesson. I learned DO NOT USE CLIP LEADS TO TEST CIRCUITS!!!! Initally, I was powering my circuit and making all of my connections between the photosensor head (2 photodiodes and 1 LED) with clip leads. This was a BAD IDEA BECAUSE CLIP LEADS ARE UNSTABLE AND IT IS VERY EASY TO SHORT A CIRCUIT IF THEY ACCIDENTALLY TOUCH! I did not realize this important lesson until my photosensor circuit was once again burning. Confused as to why my circuit was once again burning, I foolishly touched the voltage regulator. As you can see on the top voltage regulator in the photo below, my finger left its mark on the smoldering voltage regulator. As you cannot see the wincing on my face as I try to type this long elog, I will painfully type that the voltage regulator left its own mark on my finger (an ugly sore little welt). Suresh has taught me a valuable lesson: WHEN DEALING WITH SOMETHING OF QUESTIONABLE/UNKNOWN TEMPERATURE, USE YOUR NOSE, NOT YOUR FINGER TO DETERMINE IF THAT COMPONENT IS HOT!!!!
To make my circuit-testing safer, upon the suggestion of Suresh, I have since removed the clip leads and inserted a 12 pin IDC component (pictured below). There are 12 pins for the 6 inputs I will get from each of the 2 photosensor heads. I have requested orders for a 16 pin IDC connector, 15 pin Dsub male part, 15 pin Dsub feed-thru, 9 pin Dsub male part (2), and 9 pin Dsub feed-thru (2). After receiving these components, I should be able to safely test my circuit.
In the meanwhile, I can explore SimMechanics and try to figure out how to use the accelerometer
Since last week Wednesday, I have since found a Pomona Electronics box (thanks to Jenne)
to use for my photosensor head circuit (to house the LED and 2 photodiodes). Suresh has
shown me how to use the 9-pin Dsub connector punch, and I have punched a hole in this box
to attach the Dsub connector.
Since this past entry regarding my mechanical design for the photosensor head (Photosensor Head Lessons),
I have modified the design to use a Teflon sheet instead of a copper PCB and I have moved the LED
and photodiodes closer together, upon the suggestions of Jamie and Koji. The distance between
components is now 0.112" instead of the initial 0.28". Last night, I cut the PCB board for the LED
and photodiodes and I drilled holes onto the PCB board and Teflon sheet so that the two may be
mounted to the metal plate face of the Pomona box. I still need to cut the viewer hole for and
drill screws into the face plate.
I have also been attempting to debug my photosensor circuit (box and LED/photodiode combination).
Since this last entry (Painful Votlage Regulator and Circuit Lessons), Suresh has helped me to get the parts
that I need from the Downs Electronics lab (15 wire ribbon cable, two 9 pin D-sub connectors M,
one 15 pin D-sub connector M, one 16 pin IDC connector). Upon the suggestion of Jamie, I have
also made additional safety changes to the circuit by fixing some of the soldering connections
so that all connections are done with wires (I had a few immediate lines connected with solder).
I believe the the photosensor circuit box is finally ready for testing. I may just need some help
attaching the IDC connector to the ribbon cable. After this, I would like to resume SAFELY
testing my circuit.
I have also been exploring SimMechanics. Unfortunately, I haven't been able to run the
inverted pendulum model by Sekiguchi Takanori. Everytime I attempt to run it, it says
there is an error and it shuts down Matlab. In the meanwhile, I have been watching
SimMechanics demos and trying to understand how to build a model. I'm thinking that
maybe once I figure out how SimMechanics works, I can use the image of his model
(I can see the model but it will not run) to construct a similar one that will hopefully work.
I have also been attempting to figure out the circuitry for the pre-assembled
accelerometer (made with the LIS3106AL chip). I have been trying to use a multi-meter
to figure out what the components are (beyond the accelerometer chip, which I have
printed out the datasheet for), but have been unsuccessful at that. I have figured out
that the small 5 pin chip says LAMR and is a voltage regulator. I am hoping that if I can
find the data sheet for this voltage regulator, I can figure out the circuitry. Unfortunately,
I cannot find any datasheets for a LAMR voltage regulator. There is one by LAMAR, but
the ones I have seen are all much larger. Does anyone know what the miniature voltage
regulator below is called and if "LAMR" is short for "LAMAR"?
Since last week, I've been working on building the photosensor head and have been making adjustments to my photosensor circuit box.
Changes to photosensor circuit (for box):
1) Last week, I was reading in the two signals from the two heads through a single input. Now there are two separate inputs for the two separate photosensors
2)During one of my many voltage regulator replacements, I apparently used a 7915 voltage regulator instead of a 7805 (thanks, Koji, for pointing that out! I never would have caught that mistake X___X)
3)I was powering my 5V voltage regulator with 10V...Now I'm using 15 V (now I only need 1 power supply and 3 voltage input plugs)
I have also began assembling my first photosensor head. Here is what I have so far:
Here is what needs to be done still for the photosensor head
I need to find four Teflon washers and nuts to rigidly attach the isolated PCB (PCB, Teflon sheet combination) to the box. I already have the plastic screws in (I want to use plastic and Teflon for electrical isolation purposes, so as to not short my circuit).
I need to attach the sheath of my signal cable to the box of the photosensor head for noise reduction (plan: drill screw into photosensor head box to wrap sheath wires around)
I need to attach the D-sub to the other end of my signal cable so that it can connect to the circuit box. So far, I only have the D-sub to connect the cable to my photosensor head
Yesterday, Suresh helped to walk me through the photosensor box circuit so that I now understand what voltages to expect for my circuit box trouble-shooting. After this lesson, we figured out that the problem with my photosensor box was that the two op-amps were saturated (so I fixed the feedback!). After replacing the resistor, I got the LED to light up! I still had problems reading the voltage signals from the photodiodes. I was reading 13.5V from the op amp output, but Koji explained to me that this meant that I was too close to saturation (the photodiodes were perhaps producing too much photocurrent, bringing the output close to saturation). I switched the 150 K resistor in the feedback loop to a 3.4K resistor and have thus successfully gotten displacement-dependent voltage outputs (i.e. the voltage output fluctuates as I move my hand closer and farther from the photosensor head).
Now that I have a successful circuit to power and read outputs from one photosensor, I can begin working on the other half of the circuit to power the other photosensor!
Here is the calibration curve (displacement versus voltage output) for the photosensor head that I made with the S5971 photodiodes and L9337 LEDs. This was made using a regular mirror. The linear region appears to be between 0.4 and 0.75cm. I will need to arrange the photosensor head so it measures displacements in the linear region of this plot. This plot was made using a 287 ohm resistor.