[HELP] UART communication reception circuit for LASER communication

Hi,

In this circuit i am not able to receive the data send from a pic 16f877a via UART using a photodiode.... i need help in the receiver circuit for UART data reception only... can anyone suggest me an intermediate circuit which can be used in between the photodiode and microcontrollers Rx pin.....please help


View attachment SCHEMATICS DIAGRAM OF THE SYSTEMassdd.pdf
Thankyou.

Generally you're gonna need some strong amplification. That can be accomplished by some instrumentation amplifier (either integrated or made of 3 opamps). Look for photodiode circuits on the net.

I'd say that the critical factor is what magnitude of current does the ciode actually give in light and dark condidions and what is the baud rate.

Generally some garden variety opamp like TL07x or OP07 would be sufficient in most cases

https://www.edaboard.com/threads/198459/ this might help you

---------- Post added at 01:52 ---------- Previous post was at 01:50 ----------

i think the circuit you have posted it won't work i have done same circuit one years back but did not work

https://www.edaboard.com/threads/193758/#post917661 the circuit you have posted is already posted by mr santoshaxl i think he knows better than me i also tried this circuit but never worked

I am sure it wont work as photo Diode requires large amplification... But i am a little bit confused with the amplifier required to provide digital on off voltage for UART reception... I need help in that amplifier design section...

If the issue is not resolved yet, I would request you to check whether the optocoupling unit is outputting the required signal when inputted the data.
If not at all, there is problem in it only else error might be somewhere else.
Still, as other members are saying that it needs larger power, I request you to first check at what vtg and current, it is operated and then check if MCU is giving that much vtg and current.

scorrpeio said:

If the issue is not resolved yet, I would request you to check whether the optocoupling unit is outputting the required signal when inputted the data.
If not at all, there is problem in it only else error might be somewhere else.
Still, as other members are saying that it needs larger power, I request you to first check at what vtg and current, it is operated and then check if MCU is giving that much vtg and current.

Click to expand...

The photodiode is providing output only in few mV .... It must be amplified to atleast a voltage of 3 to 5V in order for uart to receive it...
I am stuck in the design of this amplifier stage... I dont know what type of amplifier should be used here as it uses digital signal.... If anyone knows please help....

As for selection of opamps i think almost anything will do. That of course depends on the baud rate which you want to transmit at. At som high baudrates you might want something with like 1MHz od bandwidth or cascade the amplifiers. The simplest circuit would look like that:

bias voltage and value of R1 depend on photodiode characteristics. Generally the voltage on the input of an amplifier depends on the R1 value and equals the photodiode current multiplied by the value of R1. That voltage is multiplied by an opamp in non-inverting configuration to obtain some reasonable level of signal. After that you can feed it into comparator to get a TTL square wave.


The output voltage in this circuit equals
I_PH*R1*(1+R3/R2)

So if the photodiode gives current in the order of 50 uA and R1 is 10k then The voltage across R1 is 500 mV. R3 is 9k and R2 is 1k giving the amplification of 10 V/V, then you get 5V at the output for the photodiode current of 50 uA.