Hi there. Can’t find neither in the documentation nor in the forum search engine the max working frequency of this sensor.
Basically, let’s put it in those words :
What is the minimum enlightenment time aka Enable = 5V needed for the outputs to turn up or down in an environment with 0 light?
Thanks a lot in advance for your help.
Hello.
Which QTR sensor are you inquiring about, the QTR-8A or QTR-8RC? The QTR-8A and QTR-8RC sensor arrays work differently and have different output formats. The QTR-8A sensor array outputs analog voltages, and the sampling speed will depend on the ADC used to read it. In the 8RC sensor model, each phototransistor uses a capacitor discharge circuit that allows a digital I/O line on a microcontroller to take an analog reflectance reading by measuring the discharge time of the capacitor. Meaningful results can typically be available within 1 ms (i.e. when not trying to measure subtle differences in low-reflectance scenarios), allowing up to 1 kHz sampling of all 8 sensors. You can read more about the differences in their user’s guide, here.
I am also not sure what you mean by enlightenment time. Did you mean the time between readings or the time required after the sensor is turned on?
- Jeremy
Thanks for your help!
Sorry I forgot some precisions. I would like to work with the analog device.
By enlightenment time I meant the time during which the pin Enable is 5V, and as far as I’ve understood, it’s the time during which the LEDS will be enabled.
I think you’ve answered.
For example, if I want one reading every 4ms, I will set Enable to 5V during 1ms, read the outputs, and set Enable to 0V for 3ms and so on?
I have to say it’s a bit slow for my application. Can I find a way to have a meaningful reading every 200us?
If you are planning on using the QTR-8A, I recommend keeping the sensor on the whole time. This way, you can take readings as fast your ADC will allow.
- Jeremy