NEED HELP on SENSORS!

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Weis Guy

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I will be using IR LED (transmitter) and PHOTODIODE (receiver). How can I make transmit/receive circuit that allows only a unique frequency on transmitter and receives only that kind of frequency. I'm having problems on my receiver coz it affects signals from sunlight! How to solve this kind of problem?ü
 

Typically, a PLL (Phase-Locked Loop) is used for that purpose.

If you frequency is rather low (< 500 KHz), you can use a NE567.
 

I used to use them in white line tracking robot. I used LM555 and OA to filter the frequency emitted.
 

@dghuy

I've tried using 555 timer and use astable conection and tried having it produced a 36khz frequency!.What about the reciever?

@sumsuffy

where can the PLL be applied, in []bTX?[/b] or RX?
 

in the dqhuy's proposal , with a OA, I guess the 555 produces a square signal at (let's say 36kHz. The OA is used in a band-pass filter configuration to produce a sinus at 36kHz.
In that case, you may not need any PLL.

However, according to your application, your Photodiode could receive other frequency for the environnement (ambient light at 100 or 120 Hz...).
If that the case, it seems more efficient to use a PLL on the receiver side (RX !) to filter output any unwanted frequency. (and you do not need the band-pass filter anymore...)
 

you should use the band pass filter that stops all the unwanted frequencies, that i have done in one of my design , but care ful design the band pass filter is need
 

just one thing - add a circuitity to prevent photodiode from saturation for case when direct sun light comes to surface . Of course - modulation on one side and band pass filter on receiving will be needed for sure .
 

i think that sunlight could be considered as a white noise, so to eliminate its effect is not easy.

i recommend to make a notch filter on the transmitted frequency.

Hint: IR is the most rays affected by sunlight


If u have any comment, reply me
 

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