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Topic: book "getting started with arduino" wrong schematic inside ? (Read 736 times) previous topic - next topic

PGT

The book getting started with arduino contains on page 65 a drawing on how to connect an arduino for serial input
I am not deeply into electronics but to me this drawing seams wrong, the reason i conclude that is, the Arduino has 4 anolog inputs
the way it is connected here would not allow to add more analog inputs see :


So what i am thinking is was the wiring sketch to the LDR crossed perhaps ?.
If i want to use 2 LDR's should i then use :

   5v --LDR (2)-----------analog 1
   |                                   
--5v --LDR (1)-----------analog 0
   |
   5v - resistor 1Kohm---- ground

i'm not entirely sure i or why there should be a 1K ohm between 5v and ground, maybe its for protection, i dont know why the book uses one
well maybe someone can enlight me on this on how to connect multiple analog sensors in a schematic

johnwasser

The LDR and resistor act as a voltage divider.  Each LDR needs a separate resistor:

Quote

   5v --LDR (2)-----------analog 1----- resistor 1Kohm---- ground
   |                                   
   5v --LDR (1)-----------analog 0------- resistor 1Kohm---- ground

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PGT

#2
Jun 23, 2012, 11:04 pm Last Edit: Jun 23, 2012, 11:20 pm by PGTBOOS Reason: 1
but wouldnt that be like this ?

  5v  --ldr 2 ---analog 1 --|
--|                                 |---1K ohm -- ground
  5v  --ldr 1 ---analog 0 --|


so you get strange combinations of 3 resistors and have bot ldrs connected
i like to get readings of 2 sensors to measure


or maybe i dont get the idea of voltage devider..?

johnwasser


but wouldnt that be like this ?

  5v  --ldr 2 ---analog 1 --|
--|                                 |---1K ohm -- ground
  5v  --ldr 1 ---analog 0 --|


If you study your diagram you will see that analog 0 and analog 1 are shorted together.  This means that they will aways have the same reading.  Clearly not what you want.

The voltage drop across a resistor depends on the current flow.  The current flow will depend on the total resistance in the circuit.  If two equal resistors are in series between +5 and Ground the voltage at the point between them will be 2.5V.   If the resistor to +5V has a lower value the point will be above 2.5V.  If the resistor to +5V has a higher value the point will be below 2.5V.
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PGT

#4
Jun 24, 2012, 11:03 pm Last Edit: Jun 24, 2012, 11:08 pm by PGTBOOS Reason: 1
yes but there is one ground also... so through ground it all gets connected

?

i tried this today

but hat didnt work either, for to me unknown reason the analog readout of 2 and 3 kept in a swing up and down, i wanted an independent readout

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