3 Photodiodes problem help please!

Other Hardware Robotics
1

The programming side works however I have 3 photodiodes one each on pin A1, A2 and A3.

Using 1 photo diode works well.

5 v to one side other side to a 330k resistor and the resistor to ground, the diode to resistor intersection goes to pin A1.

Readings in the range 3 to 1022, which I am happy with.

Now when I add 2 more same arraignment except the out put goes to A2 and A3 the readings go in the range of 20 to 163 max.

Ok I think it is a resistor problem but I am out of my depth.

Any help would be appreciated.

2

Please post a link to the photodiode data sheet or product page.

If the photodiodes are identical, you may have installed photodiodes 2 & 3 backwards. In any case, the voltage divider circuit (shown left in the figure below) will not work well with the Arduino ADC, and when switching ADC channels, you must throw away the first ADC result, and take the second reading.

The circuit on the right will work much better. Use just about any low voltage, rail-to-rail op amp (the LM358 is not rail-to-rail).

3

I have tried so many things each PD works on its own. Spot on but when they are in parallel it all goes to rats.

The thing is it works with PhotoResistors.

I will look at your suggestion.

4

What do you mean, "in parallel"? Post a wiring diagram.

5

image
image1920×1440 65.1 KB

Hope that works (the picture)

6

Should be OK, if you actually do have the diodes connected the right way around (as drawn). Except that the diode impedance is far too high to be connected directly to the ADC input.

Are you throwing away the first measurement, after switching ADC channels?

Post the code, using code tags.

7

Read the A1!
, A2 and A3 every 1/2 second and display the readings to help in bugging.

Spent 2 days on this, my head hurts, will look tomorrow.

I will put in Variable resistors and see how that works!

Thanks for your input.

8

Hi, thanks for the help, new day and a clear head!

Went back to first principles 3 new Photodiods, resistors, bread board and jump leads.

Made it up and it worked so used the assembled bits!

Discovered that one faulty PhotoDiode and a OC resistor.

Oh Joy!

Many thanks

Richard

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