shimadzu spectrometer project - Page 1
Forum section: electronics / projects

author: seth
author_rank: Newbie
timestamp: September 19, 2014, 09:54:55 am
content: So the other day I had this conversation with my brother. “That looks cool what are you working on?”I tell him, then I get a blank stare and an “oh ok”. So here I’d like to share what I’ve been working on.A few days ago I found a shimadzu uv-1201 spectrophotometer on eBay that was listed as “for parts turns on screen doesn’t work”. It looked like it had all its pieces and the lamps(the expensive part) both worked so I immediately bought it with the hopes that they spent 10 seconds looking at it and didn’t realize there was a contrast knob on the bottom of the thing.It arrives at my door and what do you know that wasn’t the problem. Over the next day or two I found datasheets for almost every chip and worked out the pinout to the lcd screen. Using my crappy old scope I checked the data lines and found the microprocessor was sending data. Then I checked the lcd controller and it looked good then probed the row/column drivers and they looked like they were defiantly doing something.After some head scratching I remembered that caps like to go bad and after some searching I found this video to be super helpful(, allan-w2aew).I wired up a circuit and each of the 8 caps on the board had around 10ohms esr. I replaced the caps and it turned right on.I felt like kicking myself for not checking that first.After about 3 or 4 minutes it passes its self-diagnostics yay!This is the main board. The only camera I have is my cellphone so I used a flatbed scanner to get this image. The board is actually green but it doesn’t sit flat giving it this rainbow effect. These are resized because the originals are about 300mb each.All the date codes are from ’94. Was it normal to mix smd and through hole parts then? They even used both the smd and through hole versions of the same chip(74hc367).So the photo detector is bolted to one side of the sample compartment and attached to a board marked preamp.A loose bundle of wires runs from that to the connector on the upper left. From there it goes to a low offset voltage opamp(which is placed all of 2mm from a max232 charge pump capacitor???) and then to an analog devices voltage to frequency converter.After playing with it for a few minutes I was disappointed that the built in software will let you take measurements at single wavelengths but anything more complex requires the optional ‘program pack’. I want to collect full spectra so I can play with principal component analysis (http://www.shimadzu.com/an/uv/support/uv/ap/multivariate_analysis.html) and other cool statistical voodoo.I’m planning on manually setting the wavelength to 190nm. Then after it has moved setting it to 1100nm and capturing the output from the voltage to frequency converter with one channel of my scope and the signal going to the stepper motor that moves the diffraction grating with another while it’s moving between (takes about 10s) ~1nm/ms. Then send the data to the pc to processes it.The processor has a halt pin. Could I just use that to pause in between steps to average the reading?I’m assuming that measuring the freq output with a scope would be much more accurate than wiring a micro controller with a 10bit ADC to the opamp. The data sheet I found, which dates to 2013, says it has a rise time of 0.2-1us. Should I assume 1994 specs are worse? That seems really slow for a 500 kHz (2us period) signal (full scale voltage). Would that limit how accurately its frequency can be measured?

author: ElektroQuark
author_rank: Unknown
timestamp: September 19, 2014, 10:06:49 am
content: Most of the images are missing.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 19, 2014, 02:45:51 pm
content: Quote from: EdoNork on September 19, 2014, 10:06:49 amAll there for me.

author: ElektroQuark
author_rank: Unknown
timestamp: September 19, 2014, 03:09:50 pm
content: There are now, yes.