Hello everyone! I look forward to participating on this forum, as it seems there are many resources to help a novice like me learn.

I'm simply posting this to verify my conclusions, and ask more specific questions about things I have researched and gathered so far.

I had found a project that interested me on Instructables.com. I understand that the tutorials are not professionally written, but I would like to figure out what is going on in my dilemma.

The user's schematic is attached to this post, he's using a 741 Op-Amp, which requres both ±4.5v rails. I understand that this chip is obsolete, and requires two supplies (batteries) for the necessary voltages. Although, I am wondering if this schematic he posted is written correctly, or would theoretically work. According to the research I have done, it shouldn't. But obviously he has posted this successful tutorial online.

I simply cannot get a negative voltage out of his "supply circuit". My major question here is, is the schematic correct? Or am I doing something wrong?

When I breadboard it, I either get two positive voltages, or i get zero volts. At this point I don't even know if I've blown the op-amp.

Further, could someone suggest a specific op-amp that would be good for this application?

And lastly, could anyone briefly explain to me what this schematic is actually doing (he doesn't explain) and also suggest improvements?

(the schematic posted is not in any way my own, and I do not take credit for it, it is simply a reference to another person's work online)

 

This is from the ebooks that are listed along the header of each page of this website:

http://www.allaboutcircuits.com/worksheets/opamp10.html

The junction of the two 10k resistors at the midpoint across the 9v battery is the "ground" or "common" reference point where all measurements are referenced to. If you put the negative (black) lead of your meter on this midpoint, your positive (red) lead of your meter will read +4.5v when touched to the top of the upper 10k resistor.
With the black lead still at the midpoint, the bottom of the lower resistor will read -4.5v on your meter.

TL072 or TL082's are pretty good pretty cheap op-amps.

 

It's late and I'm tired, so I'm not going to try to explain it this evening, but at least I ran the circuit in a SPICE simulation, and it does appear to work. Have a look at the attached.

Make sure that the resistor values that you are using are correct. It would be very easy to make a mistake on the resistor selection.

 

The label says, it's a square wave oscillator, and it is. As for improving it, that depends on what you want to use it for. Like, improve it how? What do you want it to do better?

 

Just noticed you're in Sanford. Skycraft Parts & Surplus is about 17 miles from downtown Sandford; it's at 2245 Fairbanks Ave. just east of the I-4 in Winter Park. You won't believe how much stuff they fit into that store. You can spend a whole day just looking at everything.

Anyway, they have a huge assortment of IC's. Can't tell you what they have offhand, as I haven't been in there for awhile, and their inventory keeps changing. I picked up some LMC6484 quad rail-to-rail input output opamps there awhile back; they aren't particularly fast (1MHz bandwidth) but they beat the stuffings out of the antique 741.

They've had LT1006 dual precision opamps, LT1007 fast precision amps, LTC1052 zero-drift low noise amps, LF411's - I found some CLC411's in there, which are video amps with a 200MHz bandwidth. - there are trays full of coin envelopes filled with all kinds of IC's besides just opamps.

Anyway, if you have time on your hands, and a list of ICs to look for, you can probably find some of them there.

 

I figured out my issue, it lies in my inexperience of building circuits from schematics. I had the ±4.5v leads connected to the wrong ends of the resistor.

SgtWookie: I Love Skycraft! it's so overwhelming with everything when I go there. Sadly, it's just far enough away were it's a trip for me to go make regular trips or a big deal to risk making a trip and getting the wrong part.

 

A 741 opamp was introduced 42 years ago. It was designed to use ONLY a 30V supply so you might be lucky to find one that works properly with only a 9V supply.

A 741 opamp has a lot of hiss and has trouble with frequencies above only 9kHz.

 

I did build a temperature control with one years back.. 18v was used; two 9v batts. It is still a useful device, but it does have it's limitations..