user17150: I'm trying to run a neopixel strip and an arduino from the same power supply using a voltage divider to get 5V to the strip.
Here are the values for my voltage divider:
R1 = 1500 Ω
R2 = 1000 Ω
Vin = 12 V
resulting in:
Vout = Vin*(R2/(R1+R2)) = 12*(1000/(1500+1000)) = 12*(1000/2500) = 12*0.4 = 4.8
When the divider is connected at its inputs but not at its outputs, I measure the expected 4.8V across R2. But as soon as I connect the neopixels, I only get about 1.6V.
Could anybody explain this || Suggest a possible solution?


user7508: Since you are connecting your pixel strip in parallel with R2, the
correct formula is
Vout = Vin × (R2∥Rp) / (R1 + (R2∥Rp))

Where Rp is the resistance of the pixel strip and
R2∥Rp = R2 × Rp / (R2 + Rp)

is the combination of R2 and Rp in parallel. From this you can see that
an output voltage of 1.6 V is consistent with a strip resistance of
300 Ω.
This is, however, somewhat oversimplified, as the I(V) characteristic of
the LED strip is probably non-linear, thus not really equivalent to a
resistor.

17150: <p>I'm trying to run a neopixel strip and an arduino from the same power supply using a voltage divider to get 5V to the strip.</p>

<p>Here are the values for my voltage divider:</p>

<p>R1 = 1500 Ω</p>

<p>R2 = 1000 Ω</p>

<p>Vin = 12 V</p>

<p>resulting in:</p>

<p>Vout = Vin*(R2/(R1+R2)) = 12*(1000/(1500+1000)) = 12*(1000/2500) = 12*0.4 = 4.8</p>

<p>When the divider is connected at its inputs but not at its outputs, I measure the expected 4.8V across R2. But as soon as I connect the neopixels, I only get about 1.6V.</p>

<p>Could anybody explain this || Suggest a possible solution?</p>

<p><a href="https://i.stack.imgur.com/xdils.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xdils.png" alt="enter image description here"></a></p>
 7508: <p>Since you are connecting your pixel strip in parallel with R2, the
correct formula is</p>

<pre><code>Vout = Vin × (R2∥Rp) / (R1 + (R2∥Rp))
</code></pre>

<p>Where Rp is the resistance of the pixel strip and</p>

<pre><code>R2∥Rp = R2 × Rp / (R2 + Rp)
</code></pre>

<p>is the combination of R2 and Rp in parallel. From this you can see that
an output voltage of 1.6&nbsp;V is consistent with a strip resistance of
300&nbsp;Ω.</p>

<p>This is, however, somewhat oversimplified, as the I(V) characteristic of
the LED strip is probably non-linear, thus not really equivalent to a
resistor.</p>
