phototransistor vers CDS

[MrDEB]

been trying to locate a CDS cell for a darkness activated switch.
looks like phototransistors are readly available.
can one just substitute a phototransistor for a CDS cell
looking at the right hand schematic for dark activated switch.
**broken link removed**
found lots of circuits using compators, op amps etc.

 

[ericgibbs]

been trying to locate a CDS cell for a darkness activated switch.
looks like phototransistors are readly available.
can one just substitute a phototransistor for a CDS cell
looking at the right hand schematic for dark activated switch.
**broken link removed**
found lots of circuits using compators, op amps etc.

hi,
The basic circuit could use a PT or PD in place of the CDS, it will most likely will mean a change in the resistor value driving/loading the CDS.

 

[duffy]

Digikey has dozens of different CDS cells readily available.

A phototransistor is very similar - its current is proportional to the light, with the CDS cell the resistance is inversely proportional to the light. The phototransistor's favorite color is almost always infra-red, the CDS cell likes a lot of different colors.

 

[blueroomelectronics]

Doesn't the Shack still carry an assortment of CDS cells?

 

[MrDEB]

yes I visited RS today and they have an assorment for $3
will try and simulate in TINA but havn't had much luck turning on the relay (12v 1028ohm coil)

 

[crutschow]

A big difference is that phototransistors and photodiodes operate with only one polarity of voltage (they won't generally work properly with AC). In contrast, a CdS cell is just a resistor which will work with either polarity voltage or AC.

 

[blueroomelectronics]

Such a simple circuit, try actually building it.

 

[duffy]

May want to go with a Darlington, MrDEB. That circuit may not have enough gain even to drive a 12 milliamp relay.

 

[MrDEB]

I tried several circuits using TINA

I tried a simulation using a 12v 1028 ohm relay but couldn't get any of the circuits to work UNTIL I droped the coil resistance to 300ohms
don't know why but will try several alternativies etc.

 

[blueroomelectronics]

Or like duffy said, use a darlington.

 

[MrDEB]

got simulation to work but?

tried several different circuits and got them to work when I used the default relay (using TINA)
found a circuit that uses fewer parts that looks easy to work with as far as pcb real estate.
**broken link removed**
most if not all the other circuits used 2-3 transistors and about the same amount of resistors.

 

[blueroomelectronics]

It's got a comparator and should work fine. At least it's a simple project, a good start vs something really complex like a spectrum analyzer or a graphic equalizer.

What sort of load is the relay going to drive?

 

[MrDEB]

other projects in the works

the relay is controlling the "cabinet mood light" circuit I came up with.The 12v supply so come night fall the cabinet lights come on.
yes I am helping someone design and build a spectrum analyzer as well as graphic eq unit. basically the same thing.

 

[blueroomelectronics]

How is a spectrum analyzer the same as a graphic equilizer?

 

[duffy]

Ugh, another 741. Why won't that thing just DIE?

 

[audioguru]

Many people still use the lousy old 741 opamp for things like audio that it wasn't designed for.

 

[MrDEB]

How is a spectrum analyzer the same as a graphic equilizer?

Not exactly the same as the spectrum analyzer showes the results of the graphic equalizer.
The two go hand in hand
if building one then its not much more to build the other.
basically same circuit is used.

 

[Bob Scott]

the relay is controlling the "cabinet mood light" circuit I came up with.The 12v supply so come night fall the cabinet lights come on.
yes I am helping someone design and build a spectrum analyzer as well as graphic eq unit. basically the same thing.

Wow. The schematic looks like it was drawn on a computer simulation of an etch-a-sketch.

I'm not a critic of drawn diagrams, just very amused by the oddity.

 

[audioguru]

Wow. The schematic looks like it was drawn on a computer simulation of an etch-a-sketch.

I'm not a critic of drawn diagrams, just very amused by the oddity.

Then it was posted as a Word Document so I can see only a small part of it after clicking on a few tools. Weird.

 

[MrDEB]

circuit schmatic done on Etch a sketch--LOL

Thats a good one.
I need to clean up connections etc. but drawing was done using EXPRESSpcb
Pretty good program considering its free.
does the pcboard design as well.
will try and convert the pic to a gif or ?? for easier viewing.
was using a screen shot prg that worked really well for converting screen shots to a gif, jepeg etc.file
need to locate on computer if I could recall the name of prg.

hoovershot or ??

Oh by the way, I had Chris (a 17yr old scout) build the circuit. I realize I have some work cut out for me as far as showing him how to layout a circuit first THEN check, recheck then start soldering.
I may build same circuit as an example. might help??
NO the circuit didn't go poof but it dosen't work.
WHY?-- I havn't had a chance to look it over.