Very basic circuit on breadboard, probably a rookie mistake. Help please.

[mccor]

I'm a long time lurker here, and have a few pedals made at this point.

I think it was on here I got the schematic for the detector section of the Dr. Quack below, and I'm pretty sure nobody else has had any issue with it:


I've breadboarded, and re-breadboarded this, and am not getting any reaction from the output LED to the input. The battery LED is on constant as it should be.

The only thing I think it could be is the way I have the op amp wired, because I'm such a noob It shouldn't be a signal issue as I have an mp3 player plugged into the input.

I've used a TL072CP

I have everything hooked up as below. Would one of you mind throwing an eye over it to see if there's anything obvious with the op amp I'm missing. I'd be very grateful.

[Kevin Mitchell]

I don't mean to sound silly but...

The opamp is connected to the power, right?

[mccor]

Not silly at all. Maybe it would be, if you were asking somebody not as silly as me.

I turns out that while I had connected the ground to pin 4, I hadn't in fact connected the positive to pin 8 presuming wrongly (like an idiot), that the power going in at pin 3 was all I needed to connect.

You prompted me to double check, & it concluded with a result. Thanks. Sorry for being such a noob!

[PRR]

> power going in at pin 3 was all I needed

Electricity ALWAYS goes in loops.

(Or not, if you don't wire the loop.)

"Cords" may look like single strings but you probably know they have two (or more) wires. Guitar cord is a center wire and an outside wrap (wire). Lamp cord is two prongs and two strands (sometimes under one jacket, sometimes a 3rd prong/wire). Car battery has the red wire to the starter and a black or bare wire coming back from the frame or engine-block.

Yes, there are situations where it "appears" to work with one wire. Car tail-lamp. Older ones had just one wire. Actually the other "wire" was the metal socket shell screwed to body-metal which returned to battery.

This is maybe something "nobody ever tells you!" Nobody is born knowing that. Some of us pick it up, then forget to ever mention it.

And many-many schematic diagrams omit power connections, because the designer KNOWS that, and assumes "everybody knows that".

When the lamp is dead, follow the LOOP, both to and from lamp and power.

Here your lamp (LED) was lit-up but (as you now get) your chip was "not lit-up". And since you can't see electricity, the broken-loop was not obvious to the eye.

[Jdansti]

I love those "apply power" fixes! It happens so often that it's the first thing I look for.  It can happen to anything from pcbs (and bread boards) to amps to household appliances. My favorite was a bass player's amp at a gig. He had set it up and tested it with no problem. Just before we started playing, the amp died. He checked where it was plugged in and there was power. The removable AC cord was plugged into the rear of the amp. He was about to tear the amp open when I pushed the removable cord's plug on the back of the amp completely into the socket and it magically started working again.

I have a cousin who is an EE and used to man a hotline for Texas Instruments in the 80's. The first thing he'd ask people when they called in with problems about their equipment was, "is it plugged in". Then he'd ask, "is it turned on"?  He said that it was amazing how many problems he solved by asking those two questions.

[bluebunny]

I love those "apply power" fixes!

I love those "insert chips" fixes.  Don't ask...   

[Jdansti]

I love those "apply power" fixes!

I love those "insert chips" fixes.  Don't ask...   

Been there too! 

[deadastronaut]

yep....