Spectrometer electronic hardware
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This page serves as a brief introduction to the electronic hardware used in the WheeTrometer Teensy. On it are photos and videos that describe how things work and our reasons for our design choices. There is a video that discusses amplifier circuits in general and one that discusses the WheeTrometer circuit specifically. It is not necessary to understand everything on this page in order to get a working spectrometer. This is here to allow you to understand how things work.
The electronic hardware you need to build a WheeTrometer Teensy include the TCD1304 (detector), an amplifier board and a Teensy 4.0 development board. If you already have a Teensy 4.1, I strongly suspect that will work, although it will require modification of the 3d printed electronics housing. The amplifier board connects to the CCD and the Teensy using headers. I would like for you to solder the headers to the Teensy and the amp board yourself.
Spectrometers require a detector to sense light intensity, an ADC to convert voltage to a digital signal and a digital device like a microcontroller to control the inputs and outputs. The detector used in the WheeTrometer Teensy is a Toshiba TCD1304 Charge Coupled Device (CCD, also called a photodiode array). It is able to read over 3600 pixels and is sensitive to light from the UV to the near IR. The output from the CCD is amplified by a factor of 1.3 and that signal is read by a 16 bit Analog to Digital Converter (ADC). The two figures to the right show photos of the electronics boards. The upper photo shows green Teensy development board attached to the purple amplifier / ADC board by the blue headers. The lower photo shows that the CCD (the chip on the top) connects via headers to the amplifier ADC board.
The image to the left shows the layout of the Wheetrometer amplifier board. This board also contains the ADC. You will notice that there are six rows of green header pin positions in the figure. The top and bottom rows are not populated but provide access to unused pins on the Teensy microcontroller. With a little work you can use these to control a light source, trigger a spectrum, run a pump or an injector, or interface with another instrument. Whatever you choose.
The second and fifth rows of pins connect the Teensy board. The inner-most pins are for the CCD headers.
Video discussing WheeTrometer circuits
The video above gives some background about circuits used in the WheeTrometer. If you are already familiar with voltage followers and op amps with inverting feedback, then there is probably not anything in this that you do not already know. The video below gives more specific information about circuits in the WheeTrometer.
The video above discusses the amplification and ADC circuits in the Wheetrometer Teensy. Mostly, I want to get across what the high and low reference voltages do. I probably should not try to talk when I am tired, but ... There you go.
ADC resolution and noise
At one point, I tried incorporating a 24 bit ADC into our spectrometer. This paragraph explains why I do not think it is worth it. The figure to the right shows output from the ADC when a constant DC voltage was input. You can see that the noise in the circuit was on the order of ~40 counts. That means that it had more than 5 bits of noise, making the output good to 19 bits at most. I did not think that the additional resolution of the 24 bit ADC was worth the added complexity and cost, so we went with a 16 bit ADC
