Hi guys,

In my project im trying to transmit 56kbit's signal using the rs232 at a distance of 50cm.
One of my tasks was to do it for 1200,4800 and 9600 which i have completed. On my receiver I have a comparator with a threshhold (+- 12V) of 0 and a high pass filter with a cut off frequency of 500hz. I'm able to detect the 56kbit at around 15/25cm ish but it just attenuates the further it goes. Any ideas how I can accomplish this?

here is the datasheet for my receiver and emitter.
emitter- https://www.rapidonline.com/pdf/58-0100.pdf
receiver- https://www.rapidonline.com/pdf/58-0105.pdf

 

- Increase the optical gain with lenses
- Use a more powerful emitter, or more emitters
- use optical bandpass filters to increase rejection of ambient light noise.

You are really doing 'baseband' communications, hard to juice up the distance without using a modulated carrier.

If you increase the receiver sensitivity, you just get more noise.
Very hard to reject all the optical noise in the environment, every LED light, CFL etc. emits a modulated light output- right in your frequency domain.

 

You could:
Increase the current through the transmit LED if not already at the maximum.
Increase the sensitivity of the receiver - we would need a schematic for more on this.
You could place the transmitter and/or receiver LED at the focus of a lens or reflector.
RS232 is quite wide band. You could use a different modulation scheme which would be easier to filter.

 

You could:
Increase the current through the transmit LED if not already at the maximum.
Increase the sensitivity of the receiver - we would need a schematic for more on this.
You could place the transmitter and/or receiver LED at the focus of a lens or reflector.
RS232 is quite wide band. You could use a different modulation scheme which would be easier to filter.

ye with my LED, im only using 80% (40mA) of it's max (50mA). I'll try maxing it.

receiver circuit
https://imgur.com/gallery/JSEGK2v?f...uUL1o426E9M81sF7knQmy9-KEI76djxHchtVNItYrr550
I'll probably try a band pass filter as well and see how it does.

 

The filter you show is a low pass not high pass filter which might be OK, but not if the cut off frequency is 500Hz.

 

The filter you show is a low pass not high pass filter which might be OK, but not if the cut off frequency is 500Hz.

Ah yes sorry, i meant low pass. I also added a high pass filter( 1nF cap and 2.2kohms) to have a cut off freq of 72kHz. Would it help if I add an amplifier on my receiver?

 

Ah yes sorry, i meant low pass. I also added a high pass filter( 1nF cap and 2.2kohms) to have a cut off freq of 72kHz. Would it help if I add an amplifier on my receiver?

Also this is what my receiver looks like (blue) yellow is my input.

 

Also this is what my receiver looks like (blue) yellow is my input.

That looks like the low pass cut off frequency is too low.
What is the receiver waveform before the filters like?

 

That looks like the low pass cut off frequency is too low.
What is the receiver waveform before the filters like?

First one is before the filter at around 40cm
Second picture is 1cm