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Chameleon Assembly


Assembly of a Chameleon involves soldering the through-hole components shown in the photo below to populate two PCB's. The small rectangular PCB (“Source”) at top left holds the LED and the larger square PCB (“Detector”) holds the detector. Once assembled, these boards are mounted onto a third circular PCB (“Chameleon”). The finished assembly is secured by four nylon screws into a cylindrical delrin cuvette holder. External connections to either an LCD display or to a PC are made via a mini-DIN connector.
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LED Source PCB

An LM317 regulator wired as a current source supplies a constant current through the source LED. The drive current controls the LED brightness and is set by the choice of on-board resistor.

TSL230 Detector PCB

This detector PCB is used for colorimetric and nephelometric measurements. It employs a TSL230 light-to-frequency converter chip - a PIC microprocessor measures the output frequency that is proportional to the incident light intensity.

TSL25x Detector PCB

For fluorescence detection, a TSL25x light-to-voltage converter is the preferred option. In this case the PIC performs analog-to-digital conversion and signal averaging to measure the incident light intensity.
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Connecting Chameleon to an LCD or Computer


Chameleon units with an LCD readout (-L suffix) are connected via a custom cable that plugs into a 6 pin mini-DIN connector at the Chameleon end and into a 4 pin mini-DIN connector at the LCD end.

The computer-connected version of Chameleon (-C suffix) requires a custom USB-to-TTL-cable (TTL-232R-5V-WE) made by Future Technology Devices International Ltd (FTDI). This comes with a USB type A connector already fitted to one end and plain wire end terminations on the other end to which a mini-DIN6 male plug must be fitted. The USB connector plugs into the PC and the mini-DIN6 plug into the corresponding socket on the Chameleon instrument.
FTDI USB-to-TTL cable pinout

There are 6 wire-ended terminations on the FTDI cable of which only four (black, red, orange and yellow) are connected to the mini-DIN6 plug for use. The other two wires (brown and green) are not connected.

The diagram at left shows the TTL-232R-5V-WE cable with its USB terminations (left) and their matching wire ends (right).

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The diagram opposite shows the pin numbering convention on a mini-DIN6 connector, as viewed when facing the pins on the connector.

Connections between a TTL-232R-5V-WE cable and the mini-DIN6 connector should then made as follows :

Black = GND, connects to mini-DIN6, pin 4
Red = +5V, connects to mini-DIN6, pin 3
Orange = Tx from PC, connects to mini-DIN6, pin 1
Yellow = Rx to PC, connects to mini-DIN6, pin 2

n.b. At the wire end the brown and green wires are left unconnected

SMT Versions of the Chameleon Detector


Since these Chameleon pages were written, the dual-in-line through hole version of the TSL230 has become difficult to obtain. A surface mount (SMT) version of the TSL230 - the TSL230RD - is readily available. Consequently, a new detector PCB has been designed to accommodate the TSL230RD, and this PCB also uses an 8-SOIC SMT 12F683 PIC microcontroller. The PCB has a header to allow the 12F683 to be programmed after the PCB has been assembled. Through hole versions of the side-looking TSL235 light-to-frequency converter and TSL25x series of light-to-voltage converters can also be installed as alternate detectors on this PCB.

A second detector board is also available to accommodate surface mount versions of the TSL235 and TSL257. These parts are designated the TSL237T and TSL257T and can be used to build a colorimeter or a fluorometer, respectively. The microcontroller on this second PCB is the 12F683, again in the 8-SOIC package.

These two new PCB’s offer consider flexibiity in choice of components that can be used during assembly.