Sorry, sometimes I can be dense until it clicks! Plus learning via email is a new experience for me and (with my experience as a now ex-teacher), I imagine it must be frustrating for you when someone doesn't get the point very quickly! So please bear with me and let me ask some direct clarifying questions . . .
Nearly all the LED's @ Maplin's are rated at 30mA - Is there any way we can use these by setting the LM3914 to give a 20mA current?
Is 25mA too close to the 30mA max? (it's just that there are some rated at 25mA)
With two LED's I can increase the field of view in a section of a corridor where the kids could see the display clearly. Would each LED would be as bright as one LED by itself since the current will not have dropped because the chip is compensating and maintaining the current level?
Dave
hi Dave,
Dont get confused with the 'rating' of devices, that usually means the recommended maximum value.
eg: a LED rated at say, 30mA will give out 'x' amount of light, but at say, 20mA will give out less light, but it will work just fine.
Problem is, some of these parameters are not linear, so half the the current dosnt necessarily mean half 'apparent' intensity.
Its best to determine by trial which works best for your application.
Ref the angle, you could use a wide angle led [emitter] or narrow angle with a diffuser [ of course the visibilty 'range' will be reduced]
I would suggest that you use 2 leds in series at about 20mA, once we have determined the performance,
then we can calculate a series resistor value from the 12Vdc to the anodes of the LED.
This resistor will warm up instead of the LM3914,, but still allow the 20mA current.
I know you are an old guy, but I can give you a few years, so dont think age is a barrier to picking up new technology...
Lets see if we can put this one to bed today.
EDIT:
when you decide the LED type, post a link or the datasheet.