Can anybody please explain the working of this circuit?

Thread Starter

sidpokhrel

Joined Apr 11, 2017
3
I am a noob in electronics and thought of doing this cool project i saw on youtube. It uses laser for transmission of music from one location and receive it using solar panel on other side.I want to make this and also know the working of this circuit. Please help.
 

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Sensacell

Joined Jun 19, 2012
2,587
Typical of random circuits on the internet- it's a really poorly designed project, probably sounds terrible, if it works at all.

The overall concept is sound, but the implementation sucks.
 

BobaMosfet

Joined Jul 1, 2009
1,177
I am a noob in electronics and thought of doing this cool project i saw on youtube. It uses laser for transmission of music from one location and receive it using solar panel on other side.I want to make this and also know the working of this circuit. Please help.
At the top left you have a signal input (phono jack) connected to the primary side of a transformer. This is isolated and voltage/current changed through the transformer. That resulting signal controls a transistor that ultimately turns the laser (bottom right) on/off to a varying degree (analog), to match the waveform of the signal coming in. The bottom left is power (likely a 9V battery), a power on/off switch with an LED so you know when it's on or off, and a 5V (LM7805) voltage regulator (bottom middle) to regulate the circuit voltage on the secondary side of the transformer to 5V. The additional diodes and capacitors are not just there for safety, but to isolate and smooth power so the signal is 'cleaner'.

The circuit is very simplistic, and will probably function for your purposes of learning. The only thing that doesn't seem to make sense is the switch from High Modulation to Full Power. High Modulation is obvious, but full-power appears to disconnect the secondary side of the transformer (eliminating your input signal), and then turns the laser output on to full power (constant).... perhaps the device will double duty as a laser pointer?
 

Thread Starter

sidpokhrel

Joined Apr 11, 2017
3
Typical of random circuits on the internet- it's a really poorly designed project, probably sounds terrible, if it works at all.

The overall concept is sound, but the implementation sucks.
hey man i just wanted to know how it works if it works at all. You don't provide much of needed info.
 

Thread Starter

sidpokhrel

Joined Apr 11, 2017
3
At the top left you have a signal input (phono jack) connected to the primary side of a transformer. This is isolated and voltage/current changed through the transformer. That resulting signal controls a transistor that ultimately turns the laser (bottom right) on/off to a varying degree (analog), to match the waveform of the signal coming in. The bottom left is power (likely a 9V battery), a power on/off switch with an LED so you know when it's on or off, and a 5V (LM7805) voltage regulator (bottom middle) to regulate the circuit voltage on the secondary side of the transformer to 5V. The additional diodes and capacitors are not just there for safety, but to isolate and smooth power so the signal is 'cleaner'.

The circuit is very simplistic, and will probably function for your purposes of learning. The only thing that doesn't seem to make sense is the switch from High Modulation to Full Power. High Modulation is obvious, but full-power appears to disconnect the secondary side of the transformer (eliminating your input signal), and then turns the laser output on to full power (constant).... perhaps the device will double duty as a laser pointer?
Thanks :)
 

DickCappels

Joined Aug 21, 2008
6,535
At low audio levels the capacitor would charge through the base and emitter and stop charging, meaning there would be little or no current going through the LED, but at aduio levels that can cause the secondary to swing the base -9V with respect to the base will cause the base-emitter junction to avalanche, thus discharging the capacitor so that it can conduct current to the base through the next half cycle.

That would result in a lot of clipping of the signal. The clipping can be helped by adding a resistor between the output of the 7805 and the end of the capacitor connected to the transformer. Start with 10k and experiment. Clearly, the designer only had a vague idea of what he was doing.
 
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