Project 4 and Photoresistors

There are 7 photoresistors that are included with my Starter Kit - 6 with a flat top and 1 with a rounded top. When reading the input values, only the one with the rounded top gets a non zero value. I have used it in all three positions so I know the board is wired correctly. Any ideas? Thanks. Brett

Hmmm... schematic diagram please Brett! Need to see how you connected these photoresistors and what other components you are using.

And what are these three positions? Standing, sitting & lying down?

Schematic diagram is exactly as it is in book. When connecting the rounded photoresisitor to A0 or A1 or A2, I get valid raw values. When I connect any flat topped photoresisitor to any of these inputs, I get raw values 0 to 7.

Standing up.

Schematic diagram is exactly as it is in book.

Are you planning to send each of us a copy of the book?

Do these photo-resistors have part numbers?

bschormann: Standing up.

The three positions are standing up, standing up, and standing up?

Yes , yes and yes.

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This is like pulling teeth... What do you consider to be a "valid" reading, and what is wrong with 0 to 7?

Now, please post some pictures, from your book, showing how you were supposed to wire things up, from your circuit, showing how you actually wired it up, some close-ups of the different photoresistors and post your sketch using code tags.

Sorry, thank you for your patience. There are no part numbers on photo resistors, book is dated October 2015, first reprint December 2015. Pictures (https://drive.google.com/open?id=0B3kOh3-ZC0RrR1daYmEwbzJYN00) are book schematic, book circuit diagram, board with round photoresistor attached to A1, board with round photoresistor attached to A2 and picture of photoresistors.

photoresistors.JPG appears to show LEDs or photodiodes.

Photoresistors usually have a signature zig-zag pattern.

|500x321

Edit: Just saw the book schematic photo. You appear to have your terms mixed up, or we're not all singing from the same hymn sheet.

My bad. Photoresistor should have said phototransistor.

PaulRB: Hmmm... schematic diagram please Brett! Need to see how you connected these photoresistors and what other components you are using.

And what are these three positions? Standing, sitting & lying down?

Only if you are rather vanilla.


@bschormann,

Part of the problem is that you are assuming that the particular starter kit and project book are common to everybody here. There are dozens of starter kits, and almost as many project books. Do not assume that anyone has that book at hand to look at the schematic, or even knows what you are talking about.

Show your circuit, and give part numbers and code (in [code] tags!), as if nobody knows what you are talking about, and you will get 'there' faster.

When connecting the rounded photoresisitor to A0 or A1 or A2, I get valid raw values. When I connect any flat topped photoresisitor to any of these inputs, I get raw values 0 to 7.

For the flat topped photoresisitor, change the 10K pulldown resistor to a higher value, i.e up to 330K. I'm guessing 47K-100K would give best results.

Your circuit:

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Thank you very much. 100K worked perfectly on the flat topped photoresistors. Can you explain to me why the difference?

Without knowing the part#, it's was really just a guess. However, your readings were consistently at very low levels, indicating that the 10K value was too low for the maximum photo current being delivered.

Some photo transistors can deliver up to 10mA of photo current, other types may only produce up to 15µA ... there are many types out there to choose from, just like transistors.