Visible light communication

I am working on a project which uses visible light communication. The transmit side consists of mosfet irf J40 and bc547 transistors driving a 3W LED. At reciver side I am using a 5mm pin photo diode PD 333 and LM 358.

I have a working model currently but the operating distance between the transmitter and reciever is only 5cms. I would like to increase this distance to about 1 meter. So what factors should I take into account in order to achieve my goal of 1 Meter ?

• Please explain more about your circuit , what type of circuit do you have at the recieving side and so on. – Bhuvanesh Narayanan Jun 13 '16 at 17:05
• This is a very vague and open-ended question. Please try to be specific in what information you are looking for, and what you've already tried or studied. – Bort Jun 13 '16 at 17:14
• "can anyone say how to increase distance between transmitter n receiver?" Yes. Move them apart. Please use standard English sentences, punctuation and capitalisation. – Transistor Jun 13 '16 at 19:42
• There is a schematic editor - button on the editor toolbar. If you add a schematic of what you have created people will respond. – Transistor Jun 14 '16 at 15:19
• Can you provide the circuit diagram please – Thiru Murugan Nov 10 '17 at 3:25

One direct approach is to use the LED as much as possible. Increase the current through the LED (do not go more than the limit though). Or use a cluster of LEDs to increase the intensity of light.

I used a resistor divider for mine at the recieving end as the resistance of the sensor that I used varies with intensity. So choosing the resistor for the divider circuit is key in deciding how the intensity translates to voltage which is later given to the Recieving pin (RX in UART).

In your case you could have an OPAMP with feedback resistors to control your gain . So make sure you choose the resistors properly as they impact the gain. So more the distance then there is lesser current at the receving side which requires higher gain to tranlate the small current to a suitable voltage.

• Am using a mosfet irf J40 and bc547 transistors at the transmitter with 3W LED.At reciver 5mm pin photo diode PD 333 and LM 358 – Veena Jun 14 '16 at 8:53
• @Veena Okay, initially have a reduced baud rate (very less transmitting rate) and check if your LED is blinking properly. Usually the transmit side is easier than the receiving. Have a loo at this link thorlabs.de/tutorials.cfm?tabID=31760 . Near the end you have the opamp example. Initially I would suggest to first check if the transmit side is working then separately check if the reciving side is working and then integrate both. Have a multimeter at the recieve side and flash light using a torch and see how the voltage varies . Make some observations and then integrate both sides. – Bhuvanesh Narayanan Jun 14 '16 at 9:04
• @ bhuvanesh..it's actually working ,but distance I could achieve is very low about 5 cm..I wanna increase my distance up-to a one meter – Veena Jun 14 '16 at 10:26
• @Veena okay, the feedback resistor in your opamp could increase your gain therby giving the needed voltage. Try to simulate your case with different resistors in LtSpice or some such software, this will put you in the right path in choosing the right resistance. – Bhuvanesh Narayanan Jun 14 '16 at 14:43
• @bhuvanesh thank u..so is it enough to design only the receiver for same transmitter? – Veena Jun 18 '16 at 13:39
• More power OR more power into more LEDs.
• Focus techniques so that the light is projected only where it is needed.
• Use a focussed laser diode (with care)
• Cut down on external light interference (AC coupling)
• Use error correction techniques
• A better lower noise photodiode
• A photodiode with more surface area (if data rates permit)
• Thank u..What correction techniques can b used – Veena Jun 14 '16 at 10:30
• Standard digital error correction algorithms on data or plenty and should be defined in many places on the internet. Basically you add bits to the transmission that allow you to detect and sometimes correct bad data. You avoid block contamination from spikes of noise by spreading the bits of each byte around. It's a big subject so I'd advise you do some research. – Andy aka Jun 14 '16 at 11:04

Read up on signal receivers, for instance radio receivers and especially IR remote receivers, work. The essence is (after you tried all Andy's suggestions) to use your signal to modulate a higher-frequency siganl, and use a narrow-band receiver and amplify the signal that passes through that narrow band (and after that, demodulate).

Are you totally stuck on using visible light? IR remote receivers are pretty optimized thingies are cost next to nothing.

• I have to use visible light – Veena Jun 14 '16 at 8:50