I want to make talking clock for people who can't see. I'm thinking about using laser diode and photo-resistor so when person's hand interrupts beam it will trigger clock to announce time. Right now I'm having difficult time finding a low power laser diode that's rated to for long constant operation. Are there such diodes that can work for years nonstop?
Why does it have to be a laser?
A collimated LED may be more sensible.
AWOL:
Why does it have to be a laser?
A collimated LED may be more sensible.
Doesn't have to be a laser, but it needs to be small and cheap 
I'm no familiar with collimated LED, is it some kind of LED with focusing lens?
Why not a touch sensor, which will last waaay longer than the led?
What sort of separation do you need?
JB_AU:
Why not a touch sensor, which will last waaay longer than the led?
I'm not sure how to embed it in the acrylic enclosure. It'll have to cover some area...
AWOL:
What sort of separation do you need?
Between emitter and sensor? About 6 inches
You probably need neither laser nor collimation.
AWOL:
You probably need neither laser nor collimation.
Modulation
I don't know of many blind people that will see the led, but the touch sensor can be the whole enclosure, there are conductive paints / foils & inks, you're expecting someone who is blind to be in the correct position in order to trigger the led, whereas the touch sensor can be accessed in any direction.
JB_AU:
I don't know of many blind people that will see the led, but the touch sensor can be the whole enclosure, there are conductive paints / foils & inks, you're expecting someone who is blind to be in the correct position in order to trigger the led, whereas the touch sensor can be accessed in any direction.
Of course I don't expect blind person to see LED. But I with my eyes closed can find where my alarm clock is located, and getting hand close enough will interrupt beam and clock will announce time, and other information. Plus clock will have large arcade buttons and special cutouts (guides) in the acrylic to locate them. Of course conductive sensor are also good idea, I just want to try several ideas. Thus my question about long lasting laser LEDs...
So I take it nobody knows if such diodes exist?
So I take it nobody knows if such diodes exist?
I personally don't (not my area of interest), but I'm not seeing any compelling reason here for them either.
I scrutinize a hundred ideas, and am lucky if 10% of them are worth it.
Your item needs to meet the needs of a niche group.
Your item will be placed in many different areas.
The item needs to not cause undue harm (physical or psychological) to the user.
Try placing the item where the majority of users will.
I like the diode/led , but.. , what happens when the led/diode stops working.
What happens to the user?
JB_AU:
I like the diode/led , but.. , what happens when the led/diode stops working.What happens to the user?
Is this a serious question? 
I guess depends on the person. If it's a sane person, he'll contact me for repair exchange it, or just go on with his/her life We are not talking about life support system here, just an alarm clock
BTW I currently make these clocks, and it just happened that because of the large display, easy to press buttons and vocal announcements of time/date/temperature/alarm settings I was approached by a physically disabled person, so I had few ides on how to modify them to make even more convenient for such people.
what happens when the led/diode stops working.
The in-built self-test detects it?
I've used more than 1,000 led's , and even though they have 100,000 Hours , some have only lasted for 2 days. Which one will last the 100K Hours probably 5% or 95% or none.
The best led's were the original Gallium Arsenide, and thats what everyone sees in the 90's devices. Unknown that these new led/diode are safer for the (GREEN) environment. hmmmm!
AWOL:
what happens when the led/diode stops working.
The in-built self-test detects it?
Ah yes, excellent idea!
JB_AU:
I've used more than 1,000 led's , and even though they have 100,000 Hours , some have only lasted for 2 days. Which one will last the 100K Hours probably 5% or 95% or none.The best led's were the original Gallium Arsenide, and thats what everyone sees in the 90's devices. Unknown that these new led/diode are safer for the (GREEN) environment. hmmmm!
Hmm interesting. Perhaps pulsing laser beam will extend diod's life... I know they use them in the banks, museums, just don't know what kinds
Excellent.
Frantic hands trying to find a beam, which is now a mute point!