I have a question about a pair of photo diodes sir4045 and SGPT4045. What I am trying to figure out, is from the .pdf spec of the two devices, how do you tell how far they tx and rx just by themselves or what is that listed under in the manual, or is it not listed..? Thanks for any help

https://drive.google.com/file/d/1ArvvO00izDGqBuED4b9KA5J2YmdWNS-m/view?usp=sharing
https://drive.google.com/file/d/1GUXK6ihXlfxA6GI5rAaeIybDPAQgkT_D/view?usp=sharing

 

From the datasheet you can get a value for Radiant Intensity in milliwatts/steradian.

In case you are unfamiliar with the unit known as the steradian it is a measure of solid angle. Considering a point source there are \( 4\pi \) steradians of solid angle in a sphere. Given one of the operating conditions for the forward current,\( I_F \) , mentioned above, you can use the attenuation factor of \( 1/r^2 \) to compute the intensity at any distance from the point source.

https://en.wikipedia.org/wiki/Inverse-square_law#:~:text=The intensity (or illuminance or irradiance) of light,one-quarter the energy (in the same time period).

To compute the maximum distance to a potential receiver you would need to know the sensitivity of that receiver. This might or might not be specified.

Here is the receiver sensitivity data:

The median response would be a collector current of 3 mA with an irradiance of \( 1.0\;mW/cm^2 \). That should give you what you need.

For example if you use 6.0 mW/sr case and a distance of 100 cm, you would have:

\( \cfrac{6.0 \text{ mW/sr}}{4\pi(100\text{ cm})^2}\;=\;47.75\text{ nW}/\text{cm}^2 \)

It is doubtful this power level would provide much of a response, being several orders of magnitude too small.

 

Thanks a mil, I knew the info was their, just to lacking in gray mater to figure it out. I will have at now with your info. Thanks again

 

If you want good distance you will need to use a modulated signal and discriminating receiver. The TSOP type IR receivers are very sensitive and very good at rejecting background noise.