Thanks Ron for your ideas so far. Sorry I had to leave so abruptly yesterday. Here is a detail of what I'm trying to do. I'm trying to represent the position of the lever in the drawing. It is for a large amprage switch (1200-2000 amp). The lever accuratly depicts the position of the switch. (fully open, fully closed or somewhere in between) The object is to push a button and read an LED bar graph of the switches position. There is little room for any other type of measuring device thus the pull string mounted high. As you can see the travel of the pull string is around 1/2" from fully retracted to around 4 11/32 of the 4 3/4 fully extended device. So to answer your previous question, I'd like one to adjust the .25 - 1" range and the other to cover the 4.25 - 4.75 range.

I've been shopping for bar graphs. Can't seem to find what I want and am afraid I my have to make my own. I want a 7 or 10 light red on the bottom and green on top with yellow in between. I also want it fairly large and easily visible. Say 4" long. I thought the arrays that are available are a little small. I'm open to suggestions.

Again Ron thanks for your input and time. It is appreciated. If any other information is needed please ask.

p.s. Did you get your hot tub to sparkle?

I think you'll need individual LEDs. The LM3914 is the best part to use for the driver. You have a choice of dot mode or bar mode. Dot mode requires less power. If you want maximum brightness with bar mode, you will probably need to add resistors in series with the LEDs, to prevent overheating of the LM3914.
We can probably design something that will work if this part looks OK.

I did get the hot tub cleaned up. I procrastinated for several hours because I dreaded the job. When I got finally got around to it, the sun was high in the sky. I found out why they are called hot tubs.

 

I agree. From what I've learned the last couple of days it looks like the LM3914 would be the best driver for my application. However I have no idea how to set the upper and lower points.
If I need to build my own LED bar graph then so be it. I'm sure if this thing sells we will find a source to make them for us.
Would over heating be an issue if this device is only being activated for a couple of seconds? 10 seconds tops. Once or twice a month or year. But if resistors are what you need to do for brightness then I'd say "make it so".
I would want it set up as a bar graph though. With the single dot you wouldn't know if it's on its way opening or closing.
I can't tell you how greatful I am for your time and willingness to share your expertise. Thanks again.

p.s.
Nothing feels better on a bare butt than a clean hot tub.

 

I agree. From what I've learned the last couple of days it looks like the LM3914 would be the best driver for my application. However I have no idea how to set the upper and lower points.
If I need to build my own LED bar graph then so be it. I'm sure if this thing sells we will find a source to make them for us.
Would over heating be an issue if this device is only being activated for a couple of seconds? 10 seconds tops. Once or twice a month or year. But if resistors are what you need to do for brightness then I'd say "make it so".
I would want it set up as a bar graph though. With the single dot you wouldn't know if it's on its way opening or closing.
I can't tell you how greatful I am for your time and willingness to share your expertise. Thanks again.

p.s.
Nothing feels better on a bare butt than a clean hot tub.

The bar graph has no directional information, unless you watch the bar rise or fall. A rising or falling dot carries just as much information. Please respond.
I can design this for you, as I'm sure others here can. I'll try to get around to it sometime today and/or tomorrow.

 

Your right but I think the bar graph will be more friendly to read when there is a fault. (green with lots of yellow, no red) It's not like you can see it during operation anyway. Opening and closing of this switch is over in a fraction of a second. We just want to verify its position after operation. Again this circuit will only be activated with a push button for 3-5 seconds (long enough to read the LEDs) once or twice a year.

I'm looking at a fairchild MV5E164 or an Avago HDSP-4832 bar graph. They are smaller than I'd like but both of them have the tri color I want. 3 reds 4 yellows and 3 greens. But like I said. Your design, use what you think is best and I'll adjust.

I'm the newbie. The majority of my formal electrical training is from high school which I'll be having my 30th reunion this summer and from my Novice ham radio licence. (also just over 30 years ago) Like I mentioned earlier, I know enough to be dangerous.

Thanks again Ron. Can't wait to see what you come up with. As the kids say now days. Peace, out.

 

Have you already chosen a resistance value for the string pot?

 

The design is finished (I think). I would like to put the string pot value on the schematic before I post it.

 

the web site says it's 10K here is the link to the data sheet http://www.celesco.com/_datasheets/sp1.pdf

 

Duh! I just assumed they would offer a range of resistor values. I had looked at the datasheet, but not at the resistance.
Attached is the schematic. It could be done without the op amps, but the end point adjustments would interact, and it would not be as stable with temperature changes.
The 4.75V reference is just a nominal value, chosen to correspond with the length of the pot string in inches. The value is in no way critical, as the circuit is ratiometric. It most likely will not be 4.75V, so don't worry about it.

 

Wow that's amazing Ron. That would have taken me weeks to figure out on my Archer 130 electrical projects in one kit. And even then it probably wouldn't have worked. I can't tell you how appreciative I am for your time and expertise. I guess there's nothing left to do but build it. I promise when I get this all together I'll look you up and post some video or pics or something. Of course with a big holiday weekend coming up I'm sure I won't get all of my parts untill June.

One thing I'm not sure about. Are these individual LEDs or would it be possible to use on of the two bar graphs I described in my earlier post? I'm assumeing since there are no transistors driving the LEDs one of the bars will work. I noticed a slight difference in the current used between the two styles will that make a diff? I am quit anxious to start building. Thank you again for your time.

peace, out

 

Wow that's amazing Ron. That would have taken me weeks to figure out on my Archer 130 electrical projects in one kit. And even then it probably wouldn't have worked. I can't tell you how appreciative I am for your time and expertise. I guess there's nothing left to do but build it. I promise when I get this all together I'll look you up and post some video or pics or something. Of course with a big holiday weekend coming up I'm sure I won't get all of my parts untill June.

One thing I'm not sure about. Are these individual LEDs or would it be possible to use on of the two bar graphs I described in my earlier post? I'm assumeing since there are no transistors driving the LEDs one of the bars will work. I noticed a slight difference in the current used between the two styles will that make a diff? I am quit anxious to start building. Thank you again for your time.

peace, out

You can use a light bar or individual LEDs. Transistor drivers could also use either, but they would necessitate adding a current limiting resistor in series with each LED. The LM3914 has internal, programmable current limiting.
Both bar graphs use 10mA as the test current for the luminous intensity. One of them uses 10mA and the other 20mA for the forward voltage spec. I would be leery of 20mA, as it could cause the LM3914 to rapidly overheat unless resistors were added in series with the LEDs. If 10mA does not result in sufficient brightness, then we can talk about the resistors.

If you want me to add the light bar pin numbers to the schematic, I can do it. If I do, I will need to know what color goes at the bottom (short string extension), and what color goes at the top.

 

Thanks for the offer Ron. But that much I think I can figure out. You've done so much already. FYI Green is the short string. (switch is off you can access interier)

I'm flipping thru Newark right now looking for parts to start my build. I'll use the 10ma bar graph.

Too bad your in Idaho I'd like to buy you lunch some day. I'll see if I can't get around that somehow. If I have any more questions I'll ask them here. Thanks once again Ron.

 

Thanks for the offer Ron. But that much I think I can figure out. You've done so much already. FYI Green is the short string. (switch is off you can access interier)

I'm flipping thru Newark right now looking for parts to start my build. I'll use the 10ma bar graph.

Too bad your in Idaho I'd like to buy you lunch some day. I'll see if I can't get around that somehow. If I have any more questions I'll ask them here. Thanks once again Ron.

My take on location is you are the unfortunate one, not I.
Don't get to hasty about buying me lunch. It might not work.

 

Your right about that too Ron. I'm sure the veiw from your window is better than the one from mine.

It will work. I'm optimistic by nature.

 

Ron, since the 3914 is spec'd down to 3Vcc perhaps abandoning the 9V bat for 2 or 3 A cells would be advantageous? It would reduce the power dissipated by the Led drivers and provide a better power source with more run & shelf life. ... Just a thought.

 

Thanks CD. Yes, shelf life should be a consideration. You guys think of everything. That's why I'm here. The 9v was my idea but what do I know. I thought that would give it a better shelf life. I don't think I've ever seen an A battery. AA and AAA yes, as I'm sure you meant. I suppose that would change the values for some of the resistors?

 

Three volts is too low for some of the LEDs. You should be able to run it off three AAs (4.5V when fresh) by changing the value of R8 to 620Ω. This will set the reference voltage at about 2V. It should then work the same as with 9V.

 

I don't think I've ever seen an A battery. AA and AAA yes, as I'm sure you meant. I suppose that would change the values for some of the resistors?

Yes, A Battery was a brain fart. Once upon a time there were A & B batteries when portable equipment had vacuum tubes. AA's provide a fair amount of juice. I'm not a big fan of the 9V battery.

 

I'm not a big fan of the 9V battery.

Nor am I, but I am astounded at how long my Fisher GoldBug II, one of the best VLF metal detectors on the market, runs on a pair of them.