This video features a teardown and initial examination of an older Mel's Grio photodetector box, a transimpedance amplifier designed to convert low-level currents from photodiodes into measurable voltages. The speaker acquired the unit for a low price, intending to either repair it or use its enclosure and potentially some circuitry for a self-built version, having previously owned and sold similar devices. Upon opening, heavily corroded nickel-metal hydride batteries were discovered, alongside a surprisingly over-engineered fiber optic bundle serving as a backlight for the internal LCD display. The core circuitry includes high-precision op-amps (OP16, OP27) for amplification and buffering, range selection via switchable resistors and capacitors, and linear power regulation. Despite its initial broken state (dead display, rust), the internal electronics appear to be in surprisingly good condition, offering a promising starting point for a repair or rebuild project, potentially incorporating modern components like lithium batteries and a microcontroller.
Exploring the Mel's Grio Photodetector Box: A Teardown and Initial Analysis
0:00 Introduction to Mel's Grio: The video introduces a Mel's Grio photodetector box, a transimpedance amplifier used by optics engineers to convert photo diode currents (amps) into measurable voltages. Mel's Grio, an optics company, is no longer in business.
0:00:44 Wide Measurement Range: The device offers a broad measurement range, from 200 milliamps down to 2 nanoamps full scale.
0:01:23 Battery Powered for Low Noise: The unit is designed to be battery-powered (rechargeable NiMH) to minimize noise interference from external power sources, crucial for sensitive low-current measurements.
0:01:52 Condition and Purchase Motivation: The unit was purchased for $16 in a broken state (dead, rusty, rattling display). The speaker plans to either repair it, use its components/enclosure, or reverse-engineer its circuit to build a modern, microprocessor-controlled version.
0:03:11 Corroded Batteries Discovered: Upon opening the back, heavily corroded nickel-metal hydride (NiMH) batteries are found, indicating a major source of the unit's issues.
0:04:07 Mysterious Fiber Optic Bundle: An unexpected fiber optic bundle is found inside, initially confusing the speaker as to its purpose.
0:06:56 Core Circuitry Analysis: The main board features an OP16 op-amp as the transimpedance amplifier, an OP27 op-amp for the monitor output, and a range switch that selects different resistors and capacitors for various gain settings.
0:10:01 Fiber Optic Backlight: The fiber optic bundle is revealed to be an "over-engineered" backlight for the standard LCD display, a humorous example of an optics company applying its core expertise to a seemingly simple task.
0:11:46 Date Codes and Power Supply: Date codes on components suggest the unit was manufactured around 1989-1992. The power supply section uses standard LM317/LM337 linear regulators for plus/minus voltage regulation and includes bridge rectifiers for AC input charging.
0:13:10 Future Project Outlook: The speaker considers redesigning the power board for lithium batteries and DC-DC converters, though notes the current linear regulated, battery-powered design offers a quiet, low-noise operation, suitable for the sensitive analog circuitry which uses guard grounds.