- Components Checklist
- Schematics & PCB Design
- Build it
- Connect Sensors
- Power it On
- Tune it Up
- Printed Manual
Components Checklist
All components that you need to build your kit are included, as shown in this picture. It may look like two diodes are missing - those are not required in this version of the circuit. They might be added later for experiments with powering the circuit from the solar panels without need for the 9V battery (however we haven't yet figured out how to make it work reliably).
Bill of Material
| Designator | Quantity | Value / Description | Manufacturer Part | Supplier Part (LCSC) |
|---|---|---|---|---|
| C1, C2, C3, C4, C7, C8, C9, C10, C13 | 9 | 100uF 16V ±20% Aluminum Electrolytic Capacitor | 01EC1385 | C2831771 |
| C5, C6 | 2 | 10uF 16V ±20% Aluminum Electrolytic Capacitor | KS1C100MB070A00CV0 | C216315 |
| C11, C12 | 2 | 1uF 50V ±20% Aluminum Electrolytic Capacitor | KF010M050C110A | C62934 |
| CN1 | 1 | Headphones 3.5mm Jack | PJ3F07-5P (not exact part) | C668604 |
| CN2 | 1 | DC Power 6.2/2.0mm Barrel Jack | DC-005-2.5A-2.0 | C319099 |
| D1, D2 (do not assemble) | 2 | 40V 2A Schottky Barrier Diode | SR240 | C129830 |
| H1 | 1 | 2.54mm 4 Pin Header | 2.54-1*4P | 2718488 |
| IC1 | 1 | 3MHz Dual FET Op-Amp | TL082AD or TL082CP | C5274793 |
| LED1 | 1 | 5mm Orange LED | XL-502SURC (not exact part) | C2895484 |
| PT1, PT2 | 2 | 50kΩ Multi-turn Potentiometer | 3296W-1-503 / 8mm version | C118911 / C330434 |
| R1, R11, R12, R13, R14 | 5 | 1kΩ 250mW ±1% Resistor | MFR-25FTE52-1K | C172978 |
| R2, R3, R4 | 3 | 15kΩ 250mW ±1% Resistor | MFR-25FTE52-15K | C138212 |
| R5, R6, R7, R8 | 4 | 100kΩ 250mW ±1% Resistor | MFR-25FTE52-100K | C172965 |
| R9, R10 | 2 | 22kΩ 250mW ±1% Resistor | MFR-25FTE52-22K | C172986 |
| R15, R16, R17, R18 | 4 | 10kΩ 250mW ±1% Resistor | MFR-25FTE52-10K | C172967 |
| SW1 | 1 | Latching 30V 100mA Push Switch | XKB7070-Z | C318863 |
| T1, T2, T3, T4 | 4 | NPN 30V 625mW 100mA TO-92 BJT Transistor | BC549C or BC548C | C5455746 |
This BOM containst parts as selected when designing the PCB in EasyEDA, using their component library. It may be useful also if you prefer to source the components by yourself. The circuit isn't very demanding when it comes to precise values or parameters, so you don't need to get each part exactly as listed, various substitutes should work just as well.
Components marked as (not exact part) are included in the complete DIY kit as visually different alternatives with the same footprint. Some components supplied are substitutes to the parts above, with the same parameters. The potentiometers that you'll find in the kit use 8mm shaft, so you don't need a screwdriver to adjust them (while the picture shows the version with shorter shaft).
Schematics & PCB Design
The circuit is a combination of The Sound of Light Circuit by Andy Collinson and a classic "wide stereo" amplifier with TL082 (for example as shown in this picture, however the original article was since deleted, and it is uncertain who is the original author of the circuit). A missing capacitor was added in parallel to R1 (or R5 in our design).
You can download the schematics in the PDF format here.
Most of the signal traces are placed on top side of the board. Bottom side is covered by the ground plane.
EasyEDA provides nice visualizations of the PCB, however the components displayed in the 3D view are just for illustration, for example the stripes on resistors do not follow their values. But it is a great and precise tool to check where the components are, and how the holes and soldering pads interfere with the graphics.
Build it
It is a good idea to start soldering the components in order of their height, shortest to tallest, so they won't be in the way when soldering the rest.
This is what the bare PCB looks like. You can click on every picture for a higher resolution.
Resistors are best to solder first, as they have the lowest profile. The polarity does not matter. Please note that the illustration below does not show the correct stripe colours, all those resistors look like they are 10k. To know which resistor goes where, check the BOM, or the printed assembly guide, and follow the designators. If you lost the labels with values that were attached to the resistors, or you want to double check that you are installing correct resistor, here is a guide how to decode their color code.
For your quick reference, resistor values are as follows:
| R1, R11, R12, R13, R14 | 1k |
| R15, R16, R17, R18 | 10k |
| R2, R3, R4 | 15k |
| R5, R6, R7, R8 | 100k |
| R9, R10 | 22k |
Then continue with the 8 pin DIP socket for IC1, operational amplifier. The illustration below shows the chip soldered directly, which you can also do, but it's recommended to use the socket included in the kit, in case you need to replace this part later.
Transistors are good to solder next. Polarity is critical, one of their side is flat, and the correct orientation is shown on the PCB.
Then solder the connectors, the pin header and the LED diode. Similar to transistors, the polarity of the LED diode is marked on the PCB, the diode's flat side should match the printed outline.
Now is a good time to solder capacitors C1 to C12. Please be careful about their polarity: the positive lead is longer, and the negative lead is indicated by a stripe on the capacitor's side. To know which capacitor goes where, check the table below, or the printed assembly guide, and follow the designators.
To avoid mistakes, you may want to start with C11 and C12, which are 1uF. Then continue with C5 and C6, which are 10uF. All the remaining capacitors are 100uF.
| C1, C2, C3, C4, C7, C8, C9, C10, C13 | 100uF |
| C5, C6 | 10uF |
| C11, C12 | 1uF |
Add the SW1 switch, polarity matters if you want the circuit to be ON when the switch is locked down, and OFF when the actuator is released. If it's hard to tell where the pin 1 is, you can test the function before soldering the switch in: insert it to its position, power up the circut and observe at which position the LED light glows. Then you can rotate the switch if needed, and solder it in when you're sure that the orientation is correct.
Then solder two potentiometers PT1 and PT2, the orientation doesn't really matter, but for aesthetic and practical reasons you can follow the outline as printed on the PCB (to ensure that turning the PT1 clockwise increases the gain instead of decreasing it).
Finally, now it is safe to insert the IC1 into its socket. Correct orientation is critical, pin 1 is marked by a circular depression in the IC's package, and it should be close to the "IC1" text on the PCB.
And it's all done! This is what your board should look like. You can click on the picture to access the higher resolution.
Connect Sensors
Solar panels should be wired like this. If you are going to glue the connector on the panels, please pay attention where to put it, so the polarity when attached to the circuit board is correct.
You may want the panels to face outside of the circuit board, in which case the picture above should be flipped so the outer black wire connects to the (-) end of the pin header on the PCB, and red wire connects to the (+) end of the pin header. In the kit we include two 4-pin flat and two 4-pin angled pin headers (or one 8-pin header which you can break into two). If you use flat pin header, you will be able to install the solar panels like on the picture below. If you use angled pin header, the panels will be lying flat, in line with the main PCB.
You can assemble everything together using a flat piece of rigid material and a double-sided tape, or two sticks and hot glue gun, for example like this:
IR photodiodes can be soldered directly to the pin header:
The photodiodes can be inserted either way, the orientation changes the sound slightly.
Power it On
The circuit works well when powered from 3V to 9V, ideally from a battery as it will not add any unwanted noise or interference to the output signal.
Your DIY kit includes a short power cable with a 9V battery clip and a 5.5/2.1mm barrel jack. Alternatively, you can use a battery holder for 2-4 AA or AAA batteries with a compatible barrel jack. Holders that only have wires can be soldered directly to the contacts of the CN2 connector, at the underside of the PCB, or instead of the connector if you don't plan to use 9V batteries at all.
The powering voltage used makes a small difference - when powered from lower voltage, the output volume is slightly lower. The power consumption at 9V is 14.5mA, and at 3V it is 4.5mA.
Tune it Up
The two potentiometers control gain of the left & right stereo channel. If you look at the PCB blueprint, you can see that they are mounted the same way but wired in the opposite way. Therefore, turning the PT1 clockwise and turning PT2 anti-clockwise increases the gain. You can remember this easily: to increase gain, turn each potentiometer towards its neighbor (when the circuit board's headphone connector is facing up).
These are multi-turn potentiometers, it takes ~30 turns to go through their entire range. Once they are at the end of the range, you will hear faint clicking. In the beginning, you may want to adjust both potentiometers to somewere at the middle (~15 turns from the end position), then continue to experiment from there.
Printed Manual
Download it in JPG or PDF format.
