Hi,
I am doing a project where i need to be able to convert 14 independent LDR analog signals each into a digital reading.
This cannot be done on a standard arduino due to the limitations of ADC I/O pins. Is there another way i can increase the amount of LDRs whilst still receiving digital signals from each?
Thanks in Advance
A Mega is a standard Arduino.
Thank you!
Why LDRs? So slow.
Masseymo:
I am doing a project where i need to be able to convert 14 independent LDR analog signals each into a digital reading.This cannot be done on a standard arduino due to the limitations of ADC I/O pins. Is there another way i can increase the amount of LDRs whilst still receiving digital signals from each?
In this recent thread I proposed a circuit to multiplex an array of LDRs.
GoForSmoke:
Why LDRs? So slow.
LDRs behave more linearly than photo diodes or photo transistors, so they'd generally be preferred if the objective is to quantify the light intensity as opposed to a more binary presence/absence of light application.
MrMark:
LDRs behave more linearly than photo diodes or photo transistors, so they'd generally be preferred if the objective is to quantify the light intensity as opposed to a more binary presence/absence of light application.
Interesting.
At one time I wondered if an LDR would average flickering light to a flat value or ripple.
what's the flicker rate and at what sample rate?
MrMark:
LDRs behave more linearly than photo diodes or photo transistors...
Please explain.
An LDR has AFAIK a linear light to resistance, and a photodiode a linear light to current response.
Both linear responses are stuffed up if you connect them to an A/D with pull up resistor.
Only additional circuitry can make them linear again.
Leo..
Masseymo:
I am doing a project where i need to be able to convert 14 independent LDR analog signals each into a digital reading.
If you just want an ON/OFF indication then there is no need to use the ADC. With a suitable choice of resistor for the voltage divider an LDR will give a very good indication on a digital pin. I have about 20 of them feeding into a Mega to detect the presence of model trains.
...R
123Splat:
what's the flicker rate and at what sample rate?
The flicker would have to be faster than the LDR response time. That varies but from what I've seen it's > 10ms.
Sample rate.... what should you get if you read a sensor faster than it can change?