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At least to me, this seems to be a better circuit than the one where a transformer is used. The concept of using a transistor instead of a transformer is already known, so I cant take any credit for that, except for the actuall values and description/system design in this video.
Inplace of the radio, you can use something like a MP3 music player. You could use a computer "line out", but it most likely will need a small bit of amplification to be used good.
The supply voltage used was 4.5 Vdc. I choose this because this is the voltage required for a small laser pointer. If your not planning on using a laser pointer, you could probably use 9Vdc and just increase Rb - most likely double it, and maby a small resistor in series with the LED.
The laser-led does not tolerate voltages greater than about 5Vdc, so it would be a good idea to use a regulated 4.5 or 5Vdc voltage for initial testing purposes.
The lens is optional but can extend the range of the system. I had the lens closer to the LED initially (instead of closer to the solarpanel receiver). I noticed that a light (LED) beam the size of the solarpanel/solarcell is better than a pin-point concentrated beam on it, while experimenting with the lens in the system. I've only tested this a few feet, and I can imagine that for greater distances a second lens might be needed as a concentrator/gathering lens near the solarpanel.
If there is any noise/oscillations, you can try a small capacitor across Rb, perhaps 180pf.
Rs - can typically be about 1000 ohms, but I used 2,200 ohms with good results. Rs can go as low as maby 100 or 200 ohms, and as high as 10K probably if needed for high input signals. The volume setting on the radio was fairly low also, which is good since it would extend battery life if needed.
Rb - at 4.5Vdc power source, this "(transistor) base resistor" is about 100K, but can go lower, perhaps down to 33K and up to 300K ohms. In theory, this resitor is one of the main components that determines the bias (settings/operating point) of the transistor. It sets the dc current into the base of the transistor. It turns the transistor on, at some initial level of operation. This (dc) current (determined by Rb and the supply voltage) is essentially amplified (or multiplied if you will) by the transistor. [ you could also say that a little bit of current effectively "opens the transistor up like a valve, or turns it on", allowing a greater change in current through the transistor ]. A lower value of Rb will allow more current through the transistor, effectively turning it on more (ie. more conduction, less resistance) . In many amplifier situations (ie. "class A" amps) you would set this bias point to where the transistor is "half-on" if you will, that is set (across the transistor,or collector and emitter leads) at half the maximum voltage which is usually the supply voltage. This half-way point allows the maximum "peak-to-peak" voltage values in the output signal before the transistor/signal goes into "saturation" (full on, no more amplification possible) and/or "off"/"cutoff" (transistor essentially biased off) conditions where the output signal will not be a representation of the input signal, hence it will be a distorted signal. I indicate below in the notes that the biasing of the transistor for this circuit is near "full on" or saturation, because were not using the transistor for much amplification purposes - like an audio amplifier driving a speaker. Transistors can be used as either switches or amplifiers. Some circuits use a transistor essentially like a variable resistor in a voltage dividor circuit ( two resistors in series, with their own voltages across them ). The circuit in the video essentially uses the input signal from the radio to modulates (modifies, adjusts, shapes, determines, controls) a dc current through the LED. This current also determines the brightness of the LED, however it is practically unnoticiable in this circuit, and the solarpanel seems to sense it well though.
C1 - The capacitor in series with the solarpanel receiver must be used. This is mainly for safety since the computer soundcard puts 5Vdc onto the microphone wires to power a standard computer microphone. The value used was 0.022 uf, but can be higher. Capacitors are like open-circuits to static/DC current. Capacitors will allow AC "through" due to fluctuations or changes in charges on the plates.
C2 = perhaps 10uf and higher
Q = small black plastic, low signal, amplificaton transistor npn type
The solarpanel was from an inexpensive solar garden light. The white LED probably came from such a light also.
The LED is biased at almost full on level, perhaps 90%, and the light level fluctuations due to the radio are not that apparant.
I still have to get another small laser pointer and experiment with the system, the way I originally intended the videos to be about.
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opto-isolator interfaced triac to microcontrollerby milabut5,848 views
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