Mosaic
Well-Known Member
Hi,
I am looking for comments/advice on this approach.
In order to devise an autodimmer PIC routine fed by a Photo transistor/diode of this type
**broken link removed**
Which goes from dark (20) lux at 70uA (Coll.-Emitter current max) to 100 lux at 200uA , ambient light.
The device is NPN so its a current sink.
That 70ua works out to 5V across a 71k resistor, the 200uA is like 5V across a 33k.
I need some guidance on establishing a decent voltage difference at the ADC pin to measure. I am not sure how much the adc pin's loading will affect this. A pull up resistor is required to provide current sourcing.
Since I am looking for just light or dark switching, perhaps a small capacitor charge/ discharge cct fed by the phototransistor can be timed by a regular input pin. By forcing the cap low (with output low from the pin) and then input sampling until the cap goes logic hi might give a time that decides bright or dark.
I am looking for comments/advice on this approach.
In order to devise an autodimmer PIC routine fed by a Photo transistor/diode of this type
**broken link removed**
Which goes from dark (20) lux at 70uA (Coll.-Emitter current max) to 100 lux at 200uA , ambient light.
The device is NPN so its a current sink.
That 70ua works out to 5V across a 71k resistor, the 200uA is like 5V across a 33k.
I need some guidance on establishing a decent voltage difference at the ADC pin to measure. I am not sure how much the adc pin's loading will affect this. A pull up resistor is required to provide current sourcing.
Since I am looking for just light or dark switching, perhaps a small capacitor charge/ discharge cct fed by the phototransistor can be timed by a regular input pin. By forcing the cap low (with output low from the pin) and then input sampling until the cap goes logic hi might give a time that decides bright or dark.
