/challenges-projects/design-challenges/enchanted-objects/b/blog/posts/enchanted-objects-design-challenge---knock-knockNo voltsWhen Hans wired up the comparator circuit he could not get the output to go high. He swapped out the sensor with a simple voltage divider but still nothing. Thinking that he&#39;d got a duff component he tried another, still the output stayed on en-USTelligent Community 12https://community.element14.com/challenges-projects/design-challenges/enchanted-objects/b/blog/posts/enchanted-objects-design-challenge---knock-knockThu, 04 Jun 2015 19:32:12 GMT93d5dcb4-84c2-446f-b2cb-99731719e767:1f871cce-da80-4c58-8e89-46afbf816f01DAB0<p>Good post.</p><p>&nbsp;</p><p>These op amps can be tricky little fellows.</p><p>&nbsp;</p><p>The key thing to remember is that the op amp itself does not draw current.&nbsp; They just adjust the current flow in response to balancing the circuit as the inputs change.</p><p>&nbsp;</p><p>Subtle I admit, but that was the beauty of the design.</p><p>&nbsp;</p><p>DAB</p><img src="https://community.element14.com/aggbug?PostID=20964&AppID=117&AppType=Weblog&ContentType=0" width="1" height="1">https://community.element14.com/challenges-projects/design-challenges/enchanted-objects/b/blog/posts/enchanted-objects-design-challenge---knock-knockThu, 04 Jun 2015 16:35:44 GMT93d5dcb4-84c2-446f-b2cb-99731719e767:1f871cce-da80-4c58-8e89-46afbf816f01Workshopshed0<p>Just reviewing this circuit, I was wondering if it was possible to ground the negative input rather than having the trim pot?</p><img src="https://community.element14.com/aggbug?PostID=20964&AppID=117&AppType=Weblog&ContentType=0" width="1" height="1">