Multiple Photodiodes, how do I add(sum) output voltages correctly?
Will Eyeam
Posts: 16
On my robot, I have 17 sensors(light-to-voltage photodiode tsl12s)·total, 6 on the left and right sides=12, and 5 in the front center. For each side, 6 photodiodes will be used; 3 filtered to 10kHz and 3 filtered to 20kHz. I need to compare which photodiode(10kHz or 20kHz)·has the bigger output.
My question: what's the easiest way to sum the outputs from three·10kHz/20kHz·filtered photodiodes? I am using the interleaved adc example, so I would prefer·One sum'd output from 3 sensors because the Propeller uses 2 I/O pins for each input signal in the adc example.
My question: what's the easiest way to sum the outputs from three·10kHz/20kHz·filtered photodiodes? I am using the interleaved adc example, so I would prefer·One sum'd output from 3 sensors because the Propeller uses 2 I/O pins for each input signal in the adc example.
Comments
I think you're making this way too complicated. The Propeller can be used to accept input from the TSL12S directly and do the filtering in software. In fact, you could use one sensor for both 10kHz and 20kHz detection, perhaps simultaneously. You can also use an analog multiplexer to connect several sensors to one pin and sample them sequentially.
A couple questions:
1. Are the light sources that you're detecting being modulated by the same Propeller that's detecting them? (This would simplify things enormously.)
2. Since 20kHz is a harmonic of 10kHz, do you get any crosstalk between the two frequencies? Usually when two frequencies are being detected like this, it's better if they don't have a harmonic relationship with each other.
-Phil
Post Edited (Will Eyeam) : 4/3/2009 8:23:07 PM GMT
I did some experiments with the TSL12S and TSL14S. The TSL12S saturates in normal room light, so I used the less sensitive TSL14S instead, along with the following circuit:
I did the testing using my modem object (Bell202_modem in the OBEX). I thought this would be a good test, since it works by comparing the 1200Hz ampplitude with the 2200Hz amplitude simultaneously. I was able to communicate at 1200 baud with this setup, but only over a distance of a few inches. (The 'scope showed a signal amplitude on the Propeller pin of about 1V P-P.) So it may be necessary to use either a much brighter LED beacon or a stage of amplification ahead of the Propeller pin.
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 4/4/2009 8:28:35 AM GMT
If you run the ir beacons at 1200 and 2200 Hz you can use the modem object in the obex with some modifications to measure the relative intensities and get rid of the filters, but you will most likely need to add an agc circuit.