my first @ building a working circuit AND posting pictures! GERANIMO!!!

Hi all, I've been lurking around and learning as much as possible both here and the rest of the Internet as well as a ton of books. I set out to build a solar tracker for my self and even though it's not finished yet, I wanted to post here for some constructive criticism. This is just a small part of a big project but it was the hardest obstacle for me to over come.

Thanks for looking!

ok...so here's the theory. I set up a 1458 dual op amp with three voltage dividers, r1+r2, r3+r4 and the variable resistors to the inputs of the op amp. simple rite? this gave me an out put of just over 2 volts low on each output and a high of just over 8 volts. so I put a 5 volt zenier diode on each biased towards the outputs. the idea is to give a low of zero and a high of around 3 volts. From this point I can either build an H bridge to run a small motor or use a darlington pair to trigger dpdt relays and run a big one from a separate power source. I'm stumbling along the way but this is a start. are the diodes a bad idea?

So what will it drive? Got a plan for that? Also, the next time around with a comparator circuit you may want to think about a chip like the LM339 or similar for use as a comparator. Matter of fact give this link a read. Hope this is one of many circuits you build and enjoy.

Ron

Thanks Ron, I just edited my post to try to be more descriptive of what I'm trying to do...Heck I'm still exited from being able to find the on button on my laptop!lol.. I'm trying to leave as many options as i can so the out puts can be used with different motor sizes with out having to think about this 'first stage' circuit. Kind of like a universal fit part.
..I hope that answered the question you had and look forward to making this work for me and simple for others at my skill level.

I also just realized the diodes aren't biased correctly for there intended purpose.

You may have overlap depending on tolerance of resistors. You should put some postive feedback to give hysterisis or outputs will chatter at threshold, and use comparitors instead of op amps.

The circuit you have is basically a circuit known as a Window Comparator. However pins 3 and 6 will see the same voltage of about 4.5 volts from their respective dividers. It looks like you have a few LDRs (Light Dependent Resistors) in there? So eventually you want to drive a motor? What is the purpose of what I think are LDRs (PH1 & PH2)?

Ron

Thank you! I'll do some homework and learn from your advise. rite now I don't quite understand your approach yet; but I did see when I tested this circuit even a tiny movement made the output change. This is an extremely finicky circuit! I guess instead of overlap, what I need is some lag. Maybe a capacitor? ....like I said; I'll take what you gave me and research it!

Hi Ron, Yes it is. And you can also tell I'm still kind of lost here so thanks for your advise! the light dependent resistors are meant to be set up so that (in theory) when the same amount of light is making contact with them they have the same resistance. and therefore creating the same 4.5 divided volts.(9/2) if one has more or less resistance than the other, the voltage divider sees this (ohm's law) and the path of least resistance then guides the "power" to the appropriate input. Because this has been set up as a comparator, which ever input has the most voltage will be the one that's ON...so the best I can figure, which ever input is ON, I want to follow with a motor based on the voltage from this circuit. yes. I will be driving a motor.....eventually.. (Hey..if there are any other new people like me reading this, stick around and ask questions! Let's do this!) I hope I answered your question correctly!

Hi Ya Eddie

OK, lets look at a few things. Back in my first post I mentioned "Window Comparator" and also gave you a link to click on. That link has some very good information about comparators. I suggest you go back and read it, especially the part about window comparators. Your little circuit could use some improvement.

For example you have two dividers consisting of R1 & R2, R3 & R4. In theory each divider outputs 4.5 volts. Since you are running that reference of 4.5 volts into pins 3 and 6 of the 1458 you will have problems. The reference voltages in a window comparator should not be the same. Pin 6 should have a lower voltage than pin 6. When the input signal voltage exceeds the lower reference the output will go high and when it exceeds the higher reference it will go low. Thus a window. However, with both references the same you will have problems. Both reference voltages cannot be the same level.

Also, look at your dividers. You are using 1KΩ with 9 volts applied. Therefore R total = 2KΩ. So the current is 9 / 2000 = 4.5 mA. You could use 10KΩ resistors and reduce the current. The output would remain the same and any battery would last much longer.

There are better ways to go about this. If you would like a different circuit just let me know. Attached is a window comparator circuit taken from the link I provided.

Ron

Ok, that explanation made much more sense to me By differing the voltages slightly That where my "window" comes from, so in a sense I'm forcing this circuit to 'peek through a tiny slit' in order to stay in the off mode.(I know it's a silly analogy but I'll remember that) It took some thinking but I got that part. And yeah, More resistance should have bee obvious to me; I think what happen there was I went through the junk bow for 4 of the same resistors. I'll change that too. As for the comparator i.c., I did some reading last night and as it turns out it was designed for what I had in mind for this in the first place. WOW! It's amazing what I've picked up here already just because I was finally brave enough to ask! I plan on bread boarding something more along the line of what you suggested this morning and hope to show some good results.

Just work along at your own pace. When questions arise just ask. That is what this forum is here for.

Ron