STELLA-LabSpec
*** Advanced Build – Surface Mounting Using Solder Paste and Hot Plate***
The STELLA-Lab_Spec module for the STELLA 1.2 is a low-cost, moderate-precision 8-channel visible light spectrometer with controllable excitation sources, available in two configurations: one designed for standard cuvettes and one for PCR (polymerase chain reaction) tubes. Connected to a handheld STELLA 1.2 unit, the plugin allows users to excite sample contents with commercially available LED lamps across UV, visible, and NIR wavelengths from multiple positions, enabling investigation of fluorescence, scattering, and light transmission.
Excitation sources positioned orthogonal to the sensor optical axis allow users to characterize spectral fluorescence in biological samples tagged with fluorescent dyes, or to spectrally characterize scattering by cells and other suspended matter. The on-axis position enables spectral absorption measurements of light transmitted through the sample, supporting numerical characterization of color-change dye responses to dissolved materials such as pH indicators and nitrates.
The Lab_Spec is an open-source instrument intended to broaden access to basic laboratory spectroscopy capabilities, particularly in settings where higher-end equipment is not available. It is important to note that this instrument has not been peer reviewed, and as with all low-cost sensors in the STELLA family, it is not designed to replicate the high precision and accuracy of NASA mission instruments or professional-grade field and laboratory equipment. Results should be interpreted accordingly.
*** Build video coming soon***
STELLA-1.2 Highlights
NASA scientists and engineers at Goddard Space Flight Center, led by Paul Mirel and Mike …
At Garden City Community College in Kansas, Assistant Professor Elisa Mai integrated STELLA spectrometers into …
Garden City Community College (GCCC) in Garden City, Kansas has successfully concluded the first offering …
STELLA-LabSpec Module Build Steps
The LabSpec plugin is available in two versions distinguished by their sample holder configurations: the PCR tube version accepts 6mm diameter glass or plastic PCR (polymerase chain reaction) tubes, while the cuvette version is designed to accommodate standard laboratory cuvettes. Both versions offer the same core spectroscopic capabilities, with the choice of configuration depending on the sample containers and laboratory workflows most familiar to the user.
Specialized tools required: Magnifier, solder paste, Heat plate for electronics, tweezers, solder squeegee
Commercial Off The Shelf (COTS) Parts
| STELLA-LabSpec parts | ||||||||
|---|---|---|---|---|---|---|---|---|
| Line | Dgn | Part | Category | Qty | Type | Vendor | PN | |
| 1 | LS | Adafruit ADS1015 quad 12 bit ADC | Common | 1 | Electronics | Adafruit | 1083 | |
| 2 | LS | Adafruit half size proto board | Common | 1 | Electronics | Adafruit | 1609 | |
| 3 | LS | Adafruit MCP4728 quad 12 bit DAC | Common | 1 | Electronics | Adafruit | 4470 | |
| 4 | LS | Magnet coupler 3 pins | Common | 1 | Electronics | Adafruit | 5360 | |
| 5 | LS | Magnet coupler 4 pins | Common | 1 | Electronics | Adafruit | 5358 | |
| 6 | LS | 100kΩ resistor | Common | 4 | Electronics | Digikey | RNF14FTD100K | |
| 7 | LS | 1Ω 1% 1/4W resistor | Common | 4 | Electronics | Digikey | 13-MF0207FRE52-1RTR | |
| 8 | LS | 50Ω resistor | Common | 4 | Electronics | Digikey | RNF14FTD49R9 | |
| 9 | LS | PN2222ABU transistor | Common | 4 | Electronics | Digikey | PN2222AFS-ND | |
| 10 | LS | Socket header 3x1 pos | Common | 1 | Electronics | Digikey | SAM11930-ND | |
| 11 | LS | Socket header 3x2 pos | Common | 1 | Electronics | Digikey | SAM12901-ND | |
| 12 | LS | Socket header 3x3 pos | Common | 2 | Electronics | Digikey | SSW-103-01-G-T | |
| 13 | LS | Socket headers, 6 pos | Common | 4 | Electronics | Digikey | 4627-FH254V-06-6TBKG98 | |
| 14 | C2 | Adafruit AS7341 spectral sensor | Cuvette config | 1 | Electronics | Adafruit | 4698 | |
| 15 | C2 | White LED panel | Cuvette config | 1 | Electronics | Adafruit | 1626 | |
| 16 | C2 | Pin header 3 pos | Cuvette config | 1 | Electronics | Adafruit | 392 | |
| 17 | C2 | Pin header RA 6 pos | Cuvette config | 3 | Electronics | Adafruit | 1540 | |
| 18 | C2 | Pin header single | Cuvette config | 6 | Electronics | Adafruit | 392 | |
| 19 | C2 | 365nm LED 3mm | Cuvette config | 1 | Electronics | Digikey | 1125-MTE3660C5-UV-ND | |
| 20 | C2 | 50Ω resistor | Cuvette config | 2 | Electronics | Digikey | RNF14FTD49R9 | |
| 21 | C2 | 640nm LED 3mm | Cuvette config | 1 | Electronics | Digikey | MTE7063C2-UR | |
| 22 | C2 | Socket header 6 pos | Cuvette config | 1 | Electronics | Digikey | 4627-FH254V-06-6TBKG98 | |
| 23 | C2 | Sparkfun mini proto board | Cuvette config | 2 | Electronics | Digikey | PRT-12702 | |
| 24 | C2 | Pin header 3x2 pos | Cuvette config | 1 | Electronics | Digikey | 67997-206HLF | |
| 25 | C2 | 488nm LED smt | Cuvette config | 1 | Electronics | Mouser | 720-GCVL113KQKSV2V30 | |
| 26 | C2 | Proto-Advantage LED2 - DIP adapter | Cuvette config | 1 | Electronics | Proto-Advantage | IPC0224 | |
| 27 | C2 | Proto-Advantage small proto board | Cuvette config | 1 | Electronics | Proto-Advantage | SBB1002-1 | |
| 28 | C2 | Cuvette | Cuvette config | 1 | Consumables | Thomas Scientific | 1180W05 | |
| 29 | P2 | Adafruit AS7341 spectral sensor | PCR tube config | 1 | Electronics | Adafruit | 4698 | |
| 30 | P2 | Pin header 3 pos | PCR tube config | 1 | Electronics | Adafruit | 392 | |
| 31 | P2 | Pin header 6 pos | PCR tube config | 1 | Electronics | Adafruit | 392 | |
| 32 | P2 | Pin header single | PCR tube config | 12 | Electronics | Adafruit | 392 | |
| 33 | P2 | 365nm LED 3mm | PCR tube config | 1 | Electronics | Digikey | 1125-MTE3660C5-UV-ND | |
| 34 | P2 | 50Ω resistor | PCR tube config | 2 | Electronics | Digikey | RNF14FTD49R9 | |
| 35 | P2 | 640nm LED 3mm | PCR tube config | 1 | Electronics | Digikey | MTE7063C2-UR | |
| 36 | P2 | Socket header, RA, 6 pos | PCR tube config | 1 | Electronics | Digikey | S5481-ND | |
| 37 | P2 | Sparkfun mini proto board | PCR tube config | 1 | Electronics | Digikey | PRT-12702 | |
| 38 | P2 | Pin header 3x2 pos | PCR tube config | 1 | Electronics | Digikey | 67997-206HLF | |
| 39 | P2 | 488nm LED smt | PCR tube config | 1 | Electronics | Mouser | 720-GCVL113KQKSV2V31 | |
| 40 | P2 | Proto-Advantage LED2 - DIP adapter | PCR tube config | 1 | Electronics | Proto-Advantage | IPC0224 | |
| 41 | P2 | Proto-Advantage small proto board | PCR tube config | 1 | Electronics | Proto-Advantage | SBB1002-1 | |
| 42 | P2 | PCR 0.2mL tube | PCR tube config | 1 | Consumables | Fisher Scientific | 14-222-262 | |
3D Parts
| STELLA Lab Spec 3D parts | ||||||||
|---|---|---|---|---|---|---|---|---|
| Line | Dgn | Part | Qty | Category | Type | Vendor | P2 | .STL details, or link to part |
| 1 | LS | LS housing base | 1 | Common | 3d print part | 0.2mm layers | 0.2mm layers | |
| 2 | C2 | LS-C2 blackout shutter | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 3 | C2 | LS-C2 cuvette block | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 4 | C2 | LS-C2 cuvette block foot pair, 2up | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 5 | C2 | LS-C2 cuvette pedestal | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 6 | C2 | LS-C2 detector block | 1 | Cuvette config | 3d print part | 0.1mm layers — add support to center bridge | 0.1mm layers — add support to center bridge | |
| 7 | C2 | LS-C2 detector block assembly fixture | 1 | Cuvette config | 3d print part | 0.2mm layers | 0.2mm layers | |
| 8 | C2 | LS-C2 end cover | 1 | Cuvette config | 3d print part | 0.2mm layers | 0.2mm layers | |
| 9 | C2 | LS-C2 side LED cover, flag | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 10 | C2 | LS-C2 side LED cover, plain | 1 | Cuvette config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 11 | C2 | LS-C2 swing lid | 1 | Cuvette config | 3d print part | 0.2mm layers | 0.2mm layers | |
| 12 | P2 | LS-P2 end cover | 1 | PCR tube config | 3d print part | 0.2mm layers | 0.2mm layers | |
| 13 | P2 | LS-P2 hinge pin | 1 | PCR tube config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 14 | P2 | LS-P2 sensor retainer | 1 | PCR tube config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 15 | P2 | LS-P2 swing door | 1 | PCR tube config | 3d print part | 0.1mm layers | 0.1mm layers | |
| 16 | P2 | LS-P2 test position (single or triple source) | 1 | PCR tube config | 3d print part | 0.1mm layers — Add supports to main overhang, organic style seems to be easier to remove | 0.1mm layers — Add supports to main overhang, organic style seems to be easier to remove | |
*** Build Video Coming Soon***
| STELLA Lab Spec Main Board | |||||
|---|---|---|---|---|---|
| Step | Action | What value? | Where? | What color? | Note |
| 1 | Get board | Adafruit Permaproto Half Size | White | ||
| 2 | Cut traces | 29,30: A-B, B-C, C-D, H-i, i-J | |||
| 3 | Install magnetic couplers | 3 pos pins, 4 pos pins | 30: A, B, C, D; H, i, J | ||
| 4 | Install transistors | 2N2222 or PN2222ABU | All flats towards J: B12-13-14; B16-17-18; G12-13-14; G16-17-18 | Solder the center pin first, then straighten the body before soldering the other two pins | |
| 5 | Install shunt resistors | 1Ω 1% tol or better | B to GND each: 21, 22, 23, 24 | ||
| 6 | Install pull down resistors | 100kΩ | B to GND each: 5, 6, 7, 8 | ||
| 7 | Install bias limit resistors | 50Ω | C11-E13, C15-E17; H11-J13; H15-J17 | 49.9Ω in photos. Either value is OK. | |
| 8 | Install socket headers for devices | 6 pos, 4 places | G4-G9, D4-D9, G20-G25, D20-D25 | ||
| 9 | Install board to board stacking headers | 3x3, 2 places | ON BACK: A,B,C x 1,2,3; H,i,J x 1,2,3 | ||
| 10 | Install board to board stacking headers | 3 pos, 3 places | ON BACK: SDA 1,2,3; GND 1,2,3; 3V 1,2,3 | ||
| 11 | Install ground wires | B29-30 to GND; B9 to GND; F24 to GND | GND | ||
| 12 | Install power wires | A29-30 to 3V; B4 to 3V; F25 to 3V | +3.3V | ||
| 13 | Install SCL wires | C29-30 to SCL; J23 to SCL; J7 to SCL; G3 to SCL | i2c Serial Clock | ||
| 14 | Install SDA wires | E30 to SDA; J6 to SDA; J22 to SDA | i2c Serial Data | ||
| 15 | Install 5V wire | J29-30 to G2 | 5V | ||
| 16 | Install channel 0 wires | F1 to E12; C8 to A11; A14 to C21 | CH0 | ||
| 17 | Install channel 1 wires | E1 to A16; C7 to A15; E18 to E22 | CH1 | ||
| 18 | Install channel 2 wires | E2 to F12; E6 to F11; F14 to E23 | CH2 | ||
| 19 | Install channel 3 wires | E3 to F16; E5 to F15; F18 to E24 | CH3 | ||
| 20 | Test board for continuity and shorts | ||||
| 21 | Install MCP4728 12 bit DAC | D4-D9; Vcc, VD, VC, VB, VA, GND // G4-G9: RDY, LDAC, SDA, SCL, GND, Vcc | |||
| 22 | Install ADS1015 12 bit ADC | D20-D25; A-, A0, A1, A2, A3, A+ // G20-G25; ALRT, ADDR, SDA, SCL, GND, Vin | |||
Choose your LabSpec version:
LabSpec Cuvette Board
| STELLA-1.2 LabSpec Cuvette Cantilever Board | ||||
|---|---|---|---|---|
| Step | Action | What value? | Where? | What color? |
| 1 | Get board | Sparkfun mini | Red | |
| 2 | Using main board as a template, install pin headers | 3 pos in three places, 1 pos in six places | 1-2ABC, A4, B5, C6, C13, B14, A16, 17ABC | |
| 3 | Fixture detector board at right angles to cantilever board | 6 pos right angle pin header | G7-12 | |
| 4 | Install socket header for drop board | 6 pos stacking socket header | G1-6 | |
| 5 | Note: for the wiring, install them flat along the F row | They can stick up between D, E and F | ||
| 6 | Install ground wires | E2-F11 | GND |
|
| 7 | Install power wires | E1-F12 | +3.3V |
|
| 8 | Install SCL wires | E15-F10 | i2c Serial Clock |
|
| 9 | Install SDA wires | E17-F9 | i2c Serial Data |
|
| 10 | Install 5V wire | E14-F6 | 5V |
|
| 11 | Install channel 0 wires | E13-F5 | CH0 |
|
| 12 | Install channel 1 wires | E6-F4 | CH1 |
|
| 13 | Install channel 2 wires | E5-F3 | CH2 |
|
| 14 | Install channel 3 wires | E4-F2 | CH3 |
|
| 15 | Omit | Ground connection | at F1 | |
| 16 | Test board for continuity and shorts | |||
| STELLA LabSpec Cuvette Drop Board | ||||
| Step | Action | What value? | Where? | What color? |
| 1 | Get board | Proto-Advantage 1.1×1.7” | Epoxy color | |
| 2 | Cut traces | F1-2, F2-3, F3-4, F4-5, F5-6 F6-7 | ||
| 3 | install right angle pin headers, long pins towards the edges of the board | 6 pos, two places | B1-6, G1-6 | |
| 4 | Install current limit resistors, short to G pins on header | 50Ω, three places | FG2-C2, FG3-C3, FG4-C4 | |
| 5 | Install channel 0 wires, short to G pin on header | FG5-C5 | CH0 |
|
| 7 | Install 5V wire, short to G pin on header | FG6-C6 | 5V |
|
| 7 | Test board for continuity and shorts | |||
| STELLA Lab Spec Cuvette Excitation Board | ||||
| Step | Action | What value? | Where? | What color? |
| 1 | Get board | Sparkfun mini | Red | |
| 2 | Cut traces | F1-G1, F16-G16 | ||
| 3 | Install bottom LED, smt | 488nm | (+) FG10, (dot) FG7 | |
| 4 | Trim backlight LED panel (score with knife and snap) | Shorten the panel by 15mm | ||
| 5 | Install CH3 backlight LED panel | (+) J9, (-) J8 | ||
| 6 | Bend CH1 and CH2 LEDs, match polarity and height below | |||
| 7 | Install CH1 LED, set height with cuvette block | 365nm (for DAPI) | (+) F1, (-) G1 | |
| 8 | Install CH2 LED, set height with cuvette block | 640nm (for Cy5) | (+) F16 (-) G16 | |
| 9 | Install 5V wires | B12 – F1 (on leg), E12 – F13, G13 – F16 (on leg), i13 – i10+i9 | 5V |
|
| 10 | Install channel 0 wires | B13 – i7 | CH0 |
|
| 11 | Install channel 1 wires | B14 – i1 | CH1 |
|
| 12 | Install channel 2 wires | B15- i16 | CH2 |
|
| 13 | Install channel 3 wires | B16 – i8 | CH3 |
|
| 14 | Test board for continuity and shorts | |||
| STELLA-LabSpec Cuvette Join Drop and Excitation | ||||
| pull 6 pins from a spare header | ||||
| use the remaining plastic bar to double the spacer off the A side of the drop board | ||||
| connect the boards at A12 on the cantilever board, A17 on the excitation board | ||||
LabSpec PCR Tube Board
| STELLA Lab Spec PCR Tube Cantilever Board | ||||
|---|---|---|---|---|
| Step | Action | What value? | Where? | What color? |
| 1 | Get board | Sparkfun mini | Red | |
| 2 | Cut traces | GH7, …GH12 | ||
| 3 | Pull 6 pins from a spare pin header | |||
| 4 | Install the pins, sticking up from the board, into a right angle socket header | F7,…F12 | ||
| 5 | Using main board as a template, install pin headers | 3 pos in three places, 1 pos in six places | 1ABC, A4, B5, C6, C13, B14, A16, 17ABC | |
| 6 | Install ground wires | REAR, single layer, no crossovers | H8 – E2 | GND |
| 7 | Install power wires | REAR, single layer, no crossovers | H7 – E1 | +3.3V |
| 8 | Install SCL wires | REAR, single layer, no crossovers | H9 – E13 | i2c Serial Clock |
| 9 | Install SDA wires | REAR, single layer, no crossovers | i10 – E17 | i2c Serial Data |
| 10 | Install 5V wire | REAR, single layer, no crossovers | G10 – D14 | 5V |
| 11 | Install channel 0 wires | REAR, single layer, no crossovers | G11 – E15 | CH0 |
| 12 | Install channel 1 wires | REAR, single layer, no crossovers | G12 – E6 | CH1 |
| 13 | Install channel 2 wires | REAR, single layer, no crossovers | G8 – E5 | CH2 |
| 14 | test the sensor function with the qwiic connect cable before installing | |||
| 15 | Mount the detector board, face up, extending off the cantilever board | J7, …J12 | ||
| 16 | Test board for continuity and shorts | |||
| STELLA Lab Spec PCR tube excitation board | ||||
| Step | Action | What value? | Where? | What color? |
| 1 | Get board | Proto-Advantage 1.1×1.7” | Epoxy color | |
| 2 | Cut trace | E6-E7 | ||
| 3 | install right angle pin headers | 6 pos, 2 places | i4, … i9 | |
| 4 | test the CH0 LED polarity before installing | |||
| 5 | install CH0 LED | [+,2] G6,G7 [-,1, dot] D6,D7 | ||
| 6 | install CH1 LED | [+] F11, [-] E11 | ||
| 7 | install CH2 LED | [+] F2, [-] E2 | ||
| 8 | Install channel 0 wires | REAR: G8 – C7 | CH0 |
|
| 9 | Install current limit resistor CH1 | 50Ω | REAR: G9 – E10 | CH1 |
| 10 | Install current limit resistor CH2 | 50Ω | REAR: G4 – G1 | CH2 |
| 11 | Test board for continuity and shorts | |||
STELLA Lab Spec Plugin: Interface and measurement cycle
Measurement Cycle:
Initialization Phase
1
Begin with excitation lamp off
OFF
2
Read transistor base current
Dark current reference
3
Make spectral measurement
Dark spectrum acquisition
4
Read transistor base current
Verify dark current stability
Measurement Loop
REPEAT 3 TIMES
5
Turn lamp on
ON
6
Wait 0.5s for lamp stabilization
Thermal equilibrium period
7
Read transistor emitter current
Illuminated current measurement
8
Make spectral measurement
Sample spectrum acquisition
9
Read transistor emitter current
Post-measurement verification
10
Turn lamp off
OFF
11
Wait 0.5s between measurements
Cool-down period
Current Calculations
1
Average current values before and after each measurement
Temporal averaging for noise reduction
2
Average the three current values for measurements made with lamp on
Emitter current averaging across three cycles
3
Subtract base current average from emitter current average
Lamp current calculation
Calculation:
Lamp Current = Emitter Avg - Base Avg
Spectral Processing
4
Average spectral data in each of the eight optical bands
Lamp-on measurements only
5
Subtract dark measurement from light average
Dark current correction per band
Calculation:
Corrected Counts = Light Avg - Dark
Performance Metrics & Data Storage
6
Calculate figure of merit for each of the eight bands
Normalized performance metric
Calculation:
FM = counts / channel bandwidth / gain / integration time / lamp current
Units: counts/nm/s/A
7
Calculate usage of dynamic range of the sensor for each band
Saturation monitoring
Calculation:
DR% = 100 * raw counts / 2^16
Dynamic range percentage (16-bit ADC)
8
Record the data to the SD card
Persistent storage of all calculated metrics