Note that v0.72 was neither intended for production, nor ever produced. v0.72 was done for defining the functions, components and ports required when designing a customised Printed Circuit Board (PCB), replacing all the break out boards of the earlier versions, including v0.71.
xSpectre spectrometer version v0.72
Version 0.72 of xSpectre’s handheld spectrometer is a redesigned version preparing for shifting from break out boards to a customised PCB. Compared to earlier versions, the most important changes include:
- PCB that replaces all breakout boards,
- new micro-processor with inbuilt LiPo battery support,
- bayonet connection for the attached muzzle light sources,
- 5-pin pogo connection to the muzzle light sources, and
- stabilised power for light emitters,
PCB
v0.72 marks the transition from an assembly of break out boards to a customised Printed Circuit Board (PCB). The PCB design has been done by J2 holding AB a single person company run by Patrik Arvén. The microcontroller has been kept as a separate PCB that is fitted to the customised PCB.
Micro processor
Looking for a new micro processor with built-in functions for controlling LiPo battery charging and draining, with ports connecting directly to the battery, and with BLE, we settled for an Adafruit Feather nRF42840 Express.
Karttur’s post on Adafruit Feather nRF52840 summarises the technical details, how to setup the bootloader and then use Adafruit Feather nRF52840 with Arduino IDE.
Spectral sensor
The default spectral sensor for v0.72 is Hamamatsu miniature spectrometer C12880MA. the C12880MA sensor has 10 pins, that are hardwired on the customised PCB.
| pin | symbol | id | I/O | comment |
| 1 | +Vs | Vin | I | 5 V input |
| 2 | GND | Ground | - | Ground |
| 3 | +Vs | Vin | I | 5 V input |
| 4 | CLK | Clock pulse | I | Sensor clock pulse |
| 5 | Case | Case | - | Case connection |
| 6 | ST | Start pulse | I | Sensor start pulse |
| 7 | TRG | Trigger pulse | O | Pulse for signals |
| 8 | - | Fastening | - | Do not connect! |
| 9 | EOS | End Of Scan | O | Sensor scan end |
| 10 | Video | Video output | O | Sensor video output |
5-pin pogo connection to light sources
version 0.72 was designed to allow light sources between 1.8 and 5.0 volt, with up to 1.0 A (1000 mA). The power regulation for the light sources is a combined hardware and software solution that can be adjusted by software coding and parameter setting in realtime. To automate the power supply a 1-wire memory solution was added to the light source muzzle. The connection between the spectrometer box and the light muzzle thus in total required 5 connection pins.
At the same time a new solution for attaching and holding the muzzle in place was needed. The best alternative, used by all large camera manufacturers, is a bayonet mount. Inspired by some alternative 3D printed bayonet connections I created a customised solution (see 3D graphics of the container box and the light muzzle below).
Once the bayonet solutions was done, I choose a POGO-pin solution with a 5-pin female and a 5-pin male connection to rotate into contact when mounting the bayonet. The first bayonet plus POGO-pin solution used straight POGO-pins.
Container box
Container box v0.72 for a single customised PCB and bayonet mounted light muzzles (interactive 3D graphics).
Light muzzle for solid samples
The light muzzle with the corresponding bayonet mount. The triangular shape inside the muzzle is for a small PCB holding the light source, the female 5-pin pogo connector and the 1-wire memory unit defining the light source. the fastening for the 5-pin pogo connection (interactive 3D graphics).