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Variable dc power circuit help, "PLEASE"! Answered

I have posted 2 other questions on the variable power supply. I have put together 3 of them and none of them worked! Yes I'm a newbee to electronics and I guess I just dont understand how to read the schematic. One of the answers said that this circuit would not power a motor even if it is a very small one as this is like a direct short. Could someone please explain this. Regardless I feel so defeated, I have spent a week on this with no success. could someone please send me the wire connections as they would be on the circuit board. I was wanting this to power a small dc motor, so if this is not the circuit I need could someone send me a schematic with actual wire connections for a circuit that will give me variable power to control the speed of a dc motor. Everyone has been so nice and I apologize for my ignorance! I just want to learn so bad!!! No one locally to help me. Thanks in advance!


This circuit is very close to the one on page 10 of the LM317 datasheet. You should be able to get the motor to run at least somewhat (I don't know the specs of the motor, but you should get something out of it).

Couple of questions:

What is the voltage (DC) you are putting into the LM317? There is a minimum and maximum rating listed on the PDF above. Typically, you would want the maximum voltage needed plus 3 volts for the LM317.

Are you sure you have the diodes and capactiors placed with correct polarity? Wikipedia's diode page will help there, the electrolytic capacitors should be marked clearly.

Since you are new to all this, are you familiar with how the breadboard tie points are laid out? Wikipedia will show you if you need help there.

... and the rest of RickHarris' questions...

... and OrkSecurity's suggestion of more "book learning"...

... and Kelseymh's layout suggestion...


Here are some pics from my cell phone. not very clear but it's all I got. as far as I know I have the polarity right on the components. I studied the symbols and component identifications before attempting the circuit. Is there a site anywhere that would show it as laid out on a pcb?


I'm having a bit of a hard time following the pictures, but I think I see a possible error. According to the datasheet, the pins (looking from the front), from left to right are:

adjust, output and input.

I think you have pins connected wrong on the LM317. Verify the connections and try again. Let us know what you find.


You're right. That was the first one I put together, and went by the layout on the Radio Shack packaging which is wrong. After the first one I pulled up the data sheet and corrected that. The last one worked with a lightbulb connected until I turned the voltage up and the wiper pin started smoking on the potentiometer. Maybe I should just give up and stay with making custom handmade knives, at least I'm good at that, I've been in BLADE MAGAZINE.
I was hurt in an accident an nearly tore my right arm off. I had surgery about a month ago and I'm just bored to death since I can't use my right arm. Just wanted to learn something new. Electronics is so interesting, but maybe it's not for me. I would buy a kit so that I would have a pcb to identify what goes where, but being out of work for over a month I just don't have the money. I will be out of work for at least another 5 months, maybe by then I'll figure it out.

Give me a day or 2 and I'll try to get a schematic together for you, one that would be laid out the way a PCB would be laid out in that the leads are in their physical order, not the reordered way the drawing programs show them. That way, you can just plug them in and follow the lines. I will base it off the schematic you first posted.

Smoked the potentiometer? Something had to be miswired because the adjust pin doesn't pass a whole lot of current. The typical Radio Shack pot should last in the circuit. Since you had the bulb working, you are at least on the right track to making it work.

Sorry to hear about the arm. Hope it get stronger by the day. And don't get discouraged by the results so far. Most of us who are in electronics, whether professionally or as a hobby, made plenty of mistakes when we started.

Welcome to the community. :)


Thank you very much! That would be so nice of you. And thanks for the encouragement, I'm a workaholic and I geuss I'm just frustrated because I can't use my arm. My physical therapist says I'm progressing good. I've wanted to learn electronics for a long time and now I've got nothing but time on my hands to try to learn. Are there any good tutorial sites that you would recomend?

The first board is on top in the post. The second one is the bottom 2 pics.

Sorry it took so long, but here it is. (I hope...)



You are quite welcome.

Funny, the actual picture is bigger than they show here. Anyway, there are some basic conventions I want to clarify. The black dots are where the wires are connected, the white circles are conections for power in/out, and the "humped" wire at the first pin of IC1 crosses over the wire coming from the switch but does not connect in any way to that wire and should be either insulated/sheathed or run on the opposite side of the board. 


(MSPaint comes through again!)

If you think you're having trouble reading the schematic, I would strongly recommend that you find someone local who can work with you and help you understand what you're doing wrong. That isn't something we can really do much about remotely, unless you can break it down to very specific questions.

There is no one locally. The guys at radio shack don't know anything about electronics, they just sell parts. I just need to know the pattern of how the components are hooked up using the lm317 to make the variable control circuit.
If I could see one schematic with the layout as the wires or connections are made, then I would probably understand how to read other shematics. By the way, do you know how to add someone as a friend on this site?

Wow. Your local RadioShack actually sells parts?!? I thought they just sold cell phones and SkullCandy ear buds :-(

Do you have a breadboard and jumper wire kit that you can use to play with circuits? When I started (geez, over 30 years ago, now), one of the things that really helped me was to lay out my circuit so that it "looked like the schematic." Being able to use breadboards and those nice long pre-bent jumpers made that much easier.

I'bles isn't Failbook. If you want to get e-mail notifications when somebody publishes a new Instructable, you can do that by Subscribing to them (which Robot seems to have changed to "Follow" for all the Twits).

They don't have much, but they do have a few parts. I've got bread board, the components, but I don't know what the pre bent jumpers are.


Jumper leads or wires are just the wires you use to join together the components in the bread board. - You can buy pre bent wires to save you the trouble but don't need to really.

Personally I like to use solid core wire BUT you need to take care not to wiggle too much or it will break off in the hole and is hard to remove then.

This is the kit I used to have (from RadioShack :-). The wires are made in a bunch of different 0.1" lengths, to match breadboard hole spacing. You can use them to solder on perfboard equally well.

Breadboard jumpers

If you don't have local help... I'd suggest starting with a real electronics tutorial website until you learn the basics, *then* think about building this particular project.

Diving in at the deep end, without a lifeguard, is not usually recommended.

This is an an example of the circuit schematic I'm trying to understand.

Pulse Wave Modulation? That's the only other thing I could think of other than an uber simple circuit which consists of a potentiometer and... I dunno.

Your not really giving enough information.

1. Are you building on bread board
2 can you provide a good quality picture of what you have built
3. You can identify the different components and understand how to connect each one? ie which legs are which and which way round to put the capacitor?
4. How is the circuit you have built NOT working?

5. What test equipment have you access to - a multi meter for example and do you know how to use it?