listen to the light
Lite2Sound BC lets you explore the light in your environment by 'translating' it to sound. It does this by converting the small current from a photodiode into a voltage that's then used to drive an amplifier. Any light that fluctuates at an audible frequency, and is in the visible to near infrared spectrum, can be picked up by the circuit.
It comes packaged in a little minty tin that has a front window in it and hole for a headphone jack doubling as the project's enclosure.
Assembly and usage
The kit is surface mount using 1206 resistor/capacitor size and SOIC chip packages for easier soldering. It may be the perfect project for learning to assemble a full surface mount circuit. Below are the components used.
- x3 10µF electrolytic capacitors, Nichicon UWX1C100MCL2GB
- x2 220µF electrolytic capacitors,Multicomp MCVVT016M221EA6L
- x2 220pF C0G ceramic capacitors, Multicomp MC1206N221J500CT
- x3 100nF ceramic capacitors, Kemet C1206S104K5RACTU
- x3 10Ω resistors, Walsin WR12X10R0FTL
- x3 220Ω resistors, Walsin WR12X2200FTL
- x3 20KΩ resistors, Walsin WR12X2002FTL
- x3 2MΩ resistors, Walsin WR12W2004FTL
- x1 Schottky diode, Diodes 1N5819HW-7-F
- x1 Photodiode, On Semi QSD2030F
- x1 Photodiode, On Semi QSD2030
- x1 Low noise op-amp, Diodes TL072SG-13
- x1 Power amplifier, TI LM386MX-1/NOPB
- x1 3.5mm stereo socket, TruConnect PJ-301DM
- x1 50kΩ pot, Suntan TSR3386F-EY5-503-TR
- x2 Switch, C&K JS202011SCQN
- x1 Battery contact positive, MPD BSPCF
- x1 Battery contact negative, MPD BSPCM
- x3 12.7mm self-adhesive feet, RVFM PD.2125
- x1 Lovely PCB
- x1 Metal enclosure with a hole
- x1 Light blocking sticker for tin
Assembly instructions are in the infographic.
(Optional: if you would like to use solder paste OSH Stencils are offering a stencil at a 15% discount. Just use this link.)
Note: If soldering with hot air take care not to over heat the switches as the nylon plastic parts can melt. Because the board has big pads and traces it is advised to make sure the board generally heated up well before directly heating the component pins.
Taking it further
The Lite2Sound BC has a few possibilities for expansion and modification. For example the LM386 IC on board is a speaker driver so it can directly drive a mini speaker. A small speaker may be mounted using the two pads located to the right of D2.
You may notice vibrations can be picked up through the PCB. This is because of the microphonic properties of Class II multilayer ceramic capacitors. (Ideally we wanted to use all class I MLCCs but currently in 2017-2018 there is a shortage of affordable 100nF components.) If C2, C7 and C10 are replaced with C0G equivalents this microphonic effect can be reduced.
It is also possible to experiment with different types of enclosures and lenses. For example changing the angle of incoming light or focusing on light at a further distance.
If you find it annoying to be constantly changing the gain switch and want a more dynamic receiving range, have a look at the Lite2Sound PX from Rare Waves. It includes an automatic gain control circuit that adjusts the gain of the amplifier to match the volume of the sound coming in.
Lite2Sound BC is a collaboration between Eric Archer of Rare Waves LLC and Boldport. It is an open source design, as is most of our work. You can find the design files for the hardware and packaging at our GitHub repository. You can edit the design files using our own PCB design open source software, PCBmodE.
The PCBs were lovingly made by Eurocircuits.
Community contributions for this project are on our community site.