Faransky

It is not challenging at all. Since solar panels of this particular size react only to surrounding light, there is a simple way of testing it: You can construct a simple LED connected to a variable frequency/pulse width waveform and connect solar panel output terminals to the oscilloscope with AC coupling option. The transients will be visible as far as the minimum response time values are achieved :)

The thing is, the phototransistor has a relatively slow response time from switching on and off - around 250uS for each edge. Hence the frequency spectrum diminishes greatly, when desired testing is above 2KHz. Another disadvantage of PT is the sensitivity to spectrum provided by a light source. Solar panels are much more sensitive whose bandwidth covers all types of light sources. Since there are no energy harvesting circuits, the output voltage of the panel provides rapid changes... Which are converted to the human hearing spectrum :)

Probably, it's firmware issues. As soon as I will be able to test it, I'll provide the appropriate code ;)

As I've mentioned, blue box circuit is a DC source for the reference voltage for volume indicator. You can see that each of the LEDs is tiend to the comparator block, so I just put a trimmer potentiometer inside the circuit for volume LEDs calibration, i.e. at which peak detector output voltage the LEDs are going to turn on. About low volume, make sure that your circuit is grounded properly, since LM380 has a lot of pins that should not left floating. If you are building it according to the schematics of this particular circuit, make sure that speaker lines are connected in a differential way to the outputs of the LM380 IC.

There may be misunderstanding of the schematics due to its style.All the described circuits are connected and actually used: The thing is, that connections that share the same net name are tied to each other. Indicator circuit that I placed in a blue box is a voltage reference circuit, for the volume indicator comparison method - as you can see from the schematics above, the LM324 are used in actual circuit for comparing peak of the amplitude of the input signal, that is compared to the DC reference voltage levels.

Hi, thanks. I didn't make any simplifying schemes to this project, since it's all modular and relatively easy to understand. There is digipot IC, but the rest are PCB modules with pin description labels printed on.

Sure, it can be used with any testing equipment you want.

If you are using eBay, you can search find the module here: https://www.ebay.com/itm/DDS-AD9833-Signal-Generat...Just look for the "AD9833 DDS Signal Generator Module" key in your search.Regarding the frequency, device' code defines maximum frequency of 10.990MHz. Where Hz step resolution is 10Hz, KHz step is 1Khz, and MHz step is 1MHz.You can adjust step resolution in the frequency acquire block in the code.

There is a way to control AD9833 RAM values derivation, but this feature is not included in my design. You can check out the datasheet, and use external SPI library to do so: http://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdf

Frequency limit is based on digital potentiometer bandwith. Because it is embedded resistor array inside the IC, its inductive behavior above ~10MHz becomes significant. But regardless digipot, AD9833 module is able to produce up to 25MHz output waveform.

Contrast pot does not present in my particular case. I've tested the LCD contrast after all the circuits were soldered, it was sufficient to tie it to the ground. But it depends on design you want to make.

Device has a ~22mA consumption without load when all the peripherals are enabled including the full brightness of the LCD. Because of that, recommended to attach a battery more than equal or bigger than ~800mAh

Initially I wanted to make complete PCB design, but Idea was discarded since the whole device consists of very easy to use PCB modules that makes soldering + assmebly processes much faster :)

You can find usage of the attach\detach interrupts that I used in this project at this link: https://playground.arduino.cc/Main/PcInt . This is an example code for custom interrupts called from pin change triggers.

Thanks for notice. When I tried to re-read the assembly step, that's really what comes in mind first :)

Absolutely. And there is a way to substitute power supply unit with a 9V battery. But make sure all the bypass capacitors are present on the circuit.

Thanks for notice. The thing is, when I wrote the whole schematics step, I was on 9V value as VCC in the project, later I decided to change it to 12V. Thus, REF_DIST should be at half VCC voltage = 6V, because of its purpose to provide bias region to 741.