Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

selecting a photo transistor?

Status
Not open for further replies.

MrDEB

Well-Known Member
want to detect daylight so (the PIR triggers the PIC all day long so inserting a timing code to disable the PIR durring daylight) I can disable the PIR.
found two photo transistors but having never worked with them I am asking for suggestions.
the two I am looking at are
Fairchild QSC112 for 18 cents a piece
or
Orasham SFH309F for 42 cents each
cheap usually comes out expensive so I want something that will work.
 
that I have but ?

how to designate an input as high or low durring daylight then determing darkness as a cDs is a light sensitive resistor?
resistance increases? (decreases?) with light.
I need to disable the PIR in daylight
 
A CDS cell is a low resistance (300 ohms to 2k ohms) in light and a few Megohms in darkness. They take a few seconds to respond.
 
now its a matter which is easier?

a cDs just changes resistance while a photo transistor changes states.
need to configure a circuit for cDs. already have for photo transistor but maybe the photo transistor will consume more current than a cDs.
I even contemplated solar cells.
another option is the compariator in a PIC. I think the 18F1320 has one?? then just use that.
I recall seeing something about ADC using a PIC.
note I am just a newbi with PICs
 
A CDS from the PIC pin to +5 V and a 100K resistor from the pin to 0V.

The voltage at the pin will be:

Daytime:

100 K / 100K + 2K * 5V = 4.9 V

nighttime:

100K / 100K + 1000K * 5V = 0.45 V

The PIC will see that as logic 1 and 0.
 
Last edited:
Would think that .45 is low??

depending on battery voltage.
the photo transistors I found are 18cents each
cDs ???
may do some experimenting.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top