How To Ambient Light Sensor For Ezb To Trigger Ir Lights


Ok so I need to make ir buy a light sensor that I can place ontop of my bot through a drilled hole on Omnibots head or neck area. I will have about 25-50 5mm forward facing ir LEDs and 25-50 inside omnibots eye sockets so it illuminates the most where omnibot is looking. They will all not even draw a amp because LEDs are so low power. Any ideas of how to switch on the LEDs? I would like for it to switch the IR on when it hits a certain level of darkness. I believe my IR LEDs run on 2.5v and draw .02A thanks


THERE 2 WAYS one is use a photocell with resistor in series ,photo cell to gnd and on resistor other end v+
like a voltage divider ,where the resistor and photocell comes together is the output
then use a simple comparator circuit to turn on a transistor then switch on led

other way is get a PHIDGETS light sensor and output goes to comparator circuit

phidgets light sensor

to set the trip point use a pot,transistor needed to drive led is pnp lke 2n2222,mostly any will work
will need a base resistor from output of comparator to base of transistor ,i use like 4.7k


Ok , not to apply this. Are you suggesting this run to.USB adv then a output triggers a relay to power on the LEDs? I may have half a amp worth of whites / ir


you use a photocell board or photocell divider to op amp set up as comparator
way it works you have a photocell putting analog voltage when it dark and set point on comparator using voltage divider and when light hits the photo cell voltage drops below the set point you set and turns on a transistor switch that turns on a led
lm311 comparator circuits

you use LM311 single comparator chip AND 5 VOLTS supply single ended
if you find a photocell any type and find out the dark resistance and then get a resistor to match the value set point with 2.5 volts ,half of voltage supply ,then get a pot of twice the value of the photcell to set above or below 2.5 volt threshold
if you need help on circuit or values i can help you

on current driving of leds a mosfet will be the best answer,can drive more then 1 amp and low current drive from comparator


@ jstarne1 Or use one of these Mini Photo Cell simple and very cheap

Then feed the output into an EZB ADC port and add a script to switch on your IR lamps via EZ B digital port

Also do you really need that many IR LED's I would try a few experiments 1st and see what works with your camera


that can also work easy too,still need a mosfet as a led driver,better then using a relay
any cheap photocell will work,goldmine-elect has some very very cheap

on using A/D port on EZ board might have to adjust the values alot ?
sometime other light sources will trigger it and turn on the light,but depends on what you want to use the light detecting circuit for at work we make LUX meter ,witch uses a photo cell design
LUX is the illuminance measure of light in units LX, higher the LX brighter the room is


Why not drive the LED direct from the EZB that is what I am does take up another port on the EZB however.




kevin he has 2 problems one is it needs about .5 amp ,most outputs can only sink about 10 to 20 ma and 25 of them are .5 amps ,so the outputs would go bad

second wants to turn them on when near dark,so photo cell is only way to go,now to fine tune the photo cell on EZ-BOARD can use a pot or use a meter and measure the output voltage at the level you want lights to come on and set that voltage in EZ-ROBOT script and use mosfet to drive all of the leds,can use a relay ,like reed relay but still need a transistor to turn on the relay(i have many can sell very very cheap)

on making a comparator circuit witch is easy to make,dont need to make any scripts,or tie up analog port and is adjustable

some info about using relays and mosfets
most relays use high current on coil,not as fast switching,needs switching transistor
reed relays fast switching low current coil small size,needs switching transistor
mosfets very small size ,very low current drive ,low rds on ,sometimes dont need a switching transistor like relays need,
also higher power transistors will work ,might need a switching transistor



I must be missing something. You can easily drive multiple LEDs off a single ezb port (much less than .5 amps). A simple script can be written to turn them on when the ADC port from the photocell registers above/below a certain value. If the photo cell power is an issue, you can power itl from a different source if needed so long as you have a common ground. I use an analog accelerometer to turn on/off motors depending on tilt of the bots waist. Works great. That circuit could just as easy be a photocell and LEDs.

Comparator circuit would surely work but then you are hard wired. I would like control to be able to over ride it, if desired, and also use the photo-cell information to trigger other events.




look at the manual on EZB it says can only source or sink 25 ma,thats about 1 led,there are low current leds 1 ma ,what you might be looking at is scanning leds then you are only driving one led at a time
its near the bottom of manual under specs for max current source or sink 25ma

on comparator circuit there is a pin can be used to over-ride it,chip is 8 pin and comparator circuit can drive EZB digital input and then drive a mosfet or relay ,so you have both over ride and trigger other events
set point on photocell will be hard to set without a pot,will need a meter and measure it,or in the photocell voltage divider add a pot on top of the divider string or bottom depending on photocell circuit for EZB

photocell power is very low current ,its near 10k for most of them its near .00025 amp
or 250 ua

also when using led you need to set the current of each led ,about 470 ohms with a 5 volt source. ,7.4 volt source use near 370 ohms,but i would use a 5 volt source or source with regulator
another problem you need to look at is total current for servo's,motors,EZB,and anything else you add ,for to stay near the limits of each regulator,also stay well under
less heat