Step 6: Powering the Op Amp

Now we will connect the circuit components shown in step 5.  
First, let's power up the op amp.

1. Connect the fourth pin on the op-amp to the negative power supply (-15 V) using jumper wires. This is shown with the yellow wire.
2. Connect the seventh pin on the op-amp to the positive power supply (15 V) using jumper wires. This is shown with the red wire.
<p>For higher voltages a voltage regulator could be added too. I am going to make a type of spectrometer with this device. (Or I will try).</p><p>Light &gt;&gt;&gt; 15 W &gt;&gt;&gt; Pinhole CD case &gt;&gt;&gt;&gt; Prism glass &gt;&gt;&gt;&gt;&gt; flask cleaned &gt;&gt;&gt;&gt;&gt; several light input diodes (Photodiodes).</p>
<p>Here is the diagram.</p>
<p>Below is a digaram that uses an dual NPN transistor and capacitors could be added between base and collector to improve output.</p>
<p>Hello,</p><p>I tried to copy the circuit you describe, but i don't have a breadboard like yours with a built in supply and ground.</p><p>So I used a 24V supply and a voltage divider using two 4.7K resistors to give me -12V (the negative pole of the 24V supply), +15V (the positive pole) and ground (the middle of the voltage divider where the two resistors meet.</p><p>But the circuit doesn't work...</p><p>The output of the Op Amp stays at +11V regardless of the intensity of light hitting the photodiode...</p><p>I presume the problem is the way I am trying to set up the supply and ground, and would appreciate any advice!</p><p>Thanks.</p>
Actually, isn't the capacitor in parallel with the resistor a high-pass filter? It lets the <em>high</em> frequencies through, so the impedance of the combination is small at high frequencies, and that means the gain is also smaller at high frequencies. Otherwise, great instructable. Your explanations are clear and you have chosen a good project that will help electronics hobbyists get a grasp of the op amp. Thanks for posting!
Thanks! I think when the parallel capacitor - resistor pair is in the feedback loop of an op amp though, it really is a low pass filter. Just look at the oscilloscope screen - it's the high frequencies that we have filtered out.

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