I would not even know how to attach the circuit you drew. It had no battery or motor connection points. I can maybe change it to a 9 volt source from the wall (110 ac where I live) and change it down to 9 volts. 12 volts is not going to happen. My issue was with getting an LED to work, not the rest of the circuit that is already working.

 

Look again, the 5VDC and negative (ground) was clearly defined, and you were the first to define your load as 2.1Ω. The beauty of the chip is it works well with 12VDC as 5VDC, so the exact voltage doesn't matter. The pot shown can be adjusted to several values, say 1A to 2A. Changing the shunt resistor will allow for more ranges.

All this circuit does (which is what I think you are after) is detect current over a threshold, and turn on the LED if it is below the threshold.

This will detect if the motors are not connected and light the LED. What it will not do is detect a stalled motor condition, where you will have serious amps flowing through your wiring. If you have a fuse in the circuit (which I did not feel obliged to draw) it will blow at this point. A simple power indicator will help with this, just a resistor and an LED.

Like I said, I'll reference Radio Shack parts. If you plan on build a lot of these you would be wise to find other (mail order) sources, as Radio Shacks markups are substantial, very substantial.

 

I misread the +5V, yes I saw the ground, but okay, that could be attached to +9V or the regulated line from what you say. I am still not seeing how it would be attached with the TIP120 that is currently providing the power to the motor. I was really hoping to not have a pot to reduce manual construction time and hassle with other helpers. Also, having that much wire would really increase the size of the box. This was meant to be on the extremely small side of cordless screwdrivers (for example).

What would you consider "serious amps" for a stalled motor?

BTW: I was only using Radio Shack (since it is more convenient than waiting for mail) until I get it all completed, then looking for better prices.

 

Why are you so focused on the transistor? It is the wrong part for the job, and won't work. A common emitter transistor (which is a type of transistor configuration, a kind of circuit) doesn't begin to respond until 0.7V. This is too much voltage for the job you are wanting to do, which you haven't really explained. That transistor would be great for turning the motor on/off, but not for sensing.

You need something that interacts with the circuit as little as possible. The one I showed uses 0.05V that you are feeding the <motors?>. If you use a lot more or a lot less the shunt resistance will have to be changed, but it will work as is.

There is an old saying, "When all you have is a hammer, everything begins to look like a nail." You have to focus on the job you want to do, not on the parts you have. I could make that transistor work, but you would need about 7 more of them, and a large handful of other parts.

I hope you listened about a puny 9V battery providing 1A. I shorted a alkaline 9V once, it provided 1A of current at 0V. Your experience will be similar.

Here is the diagram I promised.

The resistors and IC are available from Radio Shack, or at least they are in the catalog. The original part I recommended, a LM393, is a dual comparator, and all I needed was one of them. The LM339 is a quad (X4) comparator, and all I needed was still one of them. If you buy quantity (more than 5) I would definitely go with another vendor, such as Mouser, Digikey, or BG Micro.

 

I did not read that you had intended on eliminating the TIP120 altogether in your previous post. I also do not see why you switched from a LM393 to an LM339. Was it just for a comparable Radio Shack part? The TI datasheet says the LM393 outputs 20mA. I need up to just over 2A. The Rshunt still seems too big to put in a case such as an electronic toothbrush (as example).
http://www.datasheetcatalog.org/datasheet/texasinstruments/lm339.pdf

 

Not to light an LED you don't. Most LEDs max out at 20ma, though there are bigger (and more expensive).

I have repeatedly asked and interpreted what you want as...

To have a LED go dark if there is a load, and light up when there isn't.

This is what I have presented.

You are playing too coy with your intended goals. A tiny 9V battery driveing a motor of unknown size and huge currents? I think I have helped all I can here. If you have any other projects I will be glad to help, but you are withholding too information for my input to be of much use.

BTW, I drew my schematics from scratch, the schematics and calculations add up in time. I figure I've spend around 4+ hours on this offline. If you want good results you need to clearly state everything up front, instead of feeding it piecemeal, and schematics are a big part of the process.

I wish you luck.

 

How about you tell us exactly what you are trying to acheive. In one single post.

What motor are you using?

What is the motor going to be doing? You have mentioned cordless screwdrivers and electronic toothbrushes. If you plan on using a motor that draws 2A for an electronic toothbrush I pity the mouth it is going into.

Where is the schematic of what you have already? We need something to build on.

Help us help you.

 

My intended goal was to add an led indicator to a working circuit. 20ma may drive an LED just fine but the load is missing that the led needs to be monitoring. I gave some similar examples of my device in hopes that it would help. The schematic I already had was in ascii in post #10 and a freehand version of the exact same thing in post #18. I apologize for not having professional schematic drawing software as I am an novice, which is also why I came to seek help on a public forum. If I had coworkers or friends that knew anything about circuits, I would have gone to them for help. If there had been a very direct "post your question this way and provide these items of information" in the stickys, I may have known everything that was required for post #1 and not induced this level of frustration with what I thought was a common indicator. At this point I may just leave it out.

 

I apologise if I sounded abrupt but it can get frustrating trying to help with what seems to be only half the info. To be honest, and I think Bill will back me up, your schematic doesn't make a lot of sense. You have a transistor that has its base floating. You have a load in the collector that "could be a motor". Is it a motor? If so what sort? You mentioned it drawing 2A. Is this realistic?

Anyway I will try and do a schematic of what I think you are looking for. I will try and do something tonight.

PS. We are not trying to drive you away. We are all here to help each other.

 

your schematic doesn't make a lot of sense. You have a transistor that has its base floating. You have a load in the collector that "could be a motor". Is it a motor? If so what sort? You mentioned it drawing 2A. Is this realistic?

Actually the OP has already provided all these information in post#19, quoted again below:

The motor load will be close to the rest of the circuit. A 9V battery (hence, changing voltages as it gets used) is regulated down to the base of the TIP120 at 5.2volts at this point I believe. The emitter goes to ground (negative from the battery), the collector goes to one end of the motor with the other motor wire going directly to +9V (positive end of the battery).

I need the LED to light up if the motor is disconnected. I need the LED to NOT light up if the motor is working fine. I do not need the LED to tell me if the TIP120 is working or not. I was hoping for a solution with a few discrete components to keep it simple.

To keep everyone focused, this is the updated drawing, showing a working circuit by OP. What he wants is to add an LED, if all that is possible.

 

Yes, the circuit that Bill posted in post #24 will do exactly what it should, when the voltage is on and the motor is not running, the led will light. Just place the circuit instead of the original motor and connect the motor to its new place.

 

5.2V there though, I'd put the proper resistor in series with the LED.