i see
i tried to make this project as simple as possible.
whats the easiest way to drop the voltage, not regulate because i dont want it to be constant. i was thinking of a step down dc - dc converter.
but the most simple way I could think of dropping the voltage was using a voltage divider.
the program and LM 3914 already does the whole calculation thing.
I just need to meet the requirements to operate the LM 3914.

 

i see
i tried to make this project as simple as possible.
whats the easiest way to drop the voltage, not regulate because i dont want it to be constant. i was thinking of a step down dc - dc converter.
but the most simple way I could think of dropping the voltage was using a voltage divider.
the program and LM 3914 already does the whole calculation thing.
I just need to meet the requirements to operate the LM 3914.

The LM3914 doesn't calculate power. It just indicates voltage. Voltage is not a measure of power unless you have a constant load resistance. Then the power is proportional to the square of the voltage.
I can show you how to use the 3914 to "measure" the output voltage. If you use a 9V battery, it probably won't last long. Were you thinking of using a 9V wall wart? If so, a 5 or 6V one would be more efficient, and put less stress on the 3914.

 

yes i know that the LM 3914 does not calculate power.
I was going to use the program WattsViewer to just label what watts each LED is when it turns on. I just want to operate the LM 3914 connect to the generator. Since the WattsViewer collects voltage, amp, and watts, I was just gonna label the LEDs accordingly after I adjust the V ref at what incements of volts do each LED light up.

BUT I need to control the input voltage like you said so.
I dont want to feed the LM 3914 30+ Volts.
That is why I'm asking how can I drop the voltage, not regulate since I need the little increments of change in voltage.

If I could get it to drop to 12V, I would just divide that by ten, adjust my V ref and have the LEDs light up at every 1.2V
Then looking at the program WattsViewer, I would see how much watts is produced at that each increment of 1.2V

 

What is the program WattsViewer?

 

its a product i bought. it comes with board that senses volts and amps as well as the program to use on the computer. so it is a separate board other than the LM 3914. This is why I am able to collect volts amps and watts.

 

its a product i bought. it comes with board that senses volts and amps as well as the program to use on the computer. so it is a separate board other than the LM 3914. This is why I am able to collect volts amps and watts.

Did you mention this before? How do you connect it to your generator?

 

maybe i didnt explain it well enough haha
sorry.
but yes it does connect to the generator.
its the only thing connected to generator right now thats collecting data nad sending it to our computer.
the positive wire go through a ring/loop thing like the hall effect in which it measures amps and then connects to the board which does the normal voltage measurements.

this is why i am not conecerned with the watts. I will just label the LEDs accordingly later

I just want to be able to connect the LM 3914 to the generator and operate properly. Do you know exactly what inputs it can take????
It says in the datasheet "Input Withstands ±35V without Damage or False Outputs"


I just need to control the input so the LM 3914 will operate

 

what is it called to when I want to decrease the volts but not regulate?
i dont want to put ceiling on it like at 12V it will be constant.

I want to step down the voltage while keeping the characteristic or shape of the curve when volts increase.
I dont know if I am making any sense at all.
I tried looking it up but Im not sure at all.
It might be variable step down transformer.

I hope you can understand what i am asking for haha

This project will be useless if it just regulates the generator to 12V you know what I mean?
I want to see the little increments of volts.
Like sizing down the output of 0-40V to 0-12V instead

 

maybe i didnt explain it well enough haha
sorry.
but yes it does connect to the generator.
its the only thing connected to generator right now thats collecting data nad sending it to our computer.
the positive wire go through a ring/loop thing like the hall effect in which it measures amps and then connects to the board which does the normal voltage measurements.

this is why i am not conecerned with the watts. I will just label the LEDs accordingly later

I just want to be able to connect the LM 3914 to the generator and operate properly. Do you know exactly what inputs it can take????
It says in the datasheet "Input Withstands ±35V without Damage or False Outputs"


I just need to control the input so the LM 3914 will operate

You won't have any amps to measure with your WattViewer unless you have a load. Do you know Ohm's law? If not, you need to.
The max useful input voltage to the 3914 depends on the supply voltage to it. I asked you in a previous post, and made a recommendation, but you ignored it.

 

yes i do know Ohm's Law. We were just testing it for now if there is an output.
Thats why now I am asking what load or what should I do to drop voltage so it can work with the LM 3914. I didnt connect it yet because I am not sure if the LM 3914 will operate or damage it.
When I just connected the wattsviewer board, it only shows voltage for now.
I am afraid to connect the LM 3914 directly to generator which was producing 38 volts when I was pedaling earlier today.

When I do connect it, then I will label what watts at each increment.

i am just asking for help to operate the LM 3914 with the generator. the wattsviewer board will do the work later
sorry if i am sounding ignorant in anyway, i am just a little excited to get this project done.
i wanted to go out today to purchase the necessary parts for the LM 3914 to operate properly with the generator.

we will actually go ahead and use the wall wart idea! thank you

but now the concern is, will the LM 3914 work directly with generator as of the way we have it set up now? if not, what should I do to make it operate?
thanks for replying alot!!! and for the help ofcourse!!!

 

yes i do know Ohm's Law. We were just testing it for now if there is an output.
Thats why now I am asking what load or what should I do to drop voltage so it can work with the LM 3914. I didnt connect it yet because I am not sure if the LM 3914 will operate or damage it.
When I just connected the wattsviewer board, it only shows voltage for now.
I am afraid to connect the LM 3914 directly to generator which was producing 38 volts when I was pedaling earlier today.

When I do connect it, then I will label what watts at each increment.

i am just asking for help to operate the LM 3914 with the generator. the wattsviewer board will do the work later
sorry if i am sounding ignorant in anyway, i am just a little excited to get this project done.
i wanted to go out today to purchase the necessary parts for the LM 3914 to operate properly with the generator.

we will actually go ahead and use the wall wart idea! thank you

but now the concern is, will the LM 3914 work directly with generator as of the way we have it set up now? if not, what should I do to make it operate?
thanks for replying alot!!! and for the help ofcourse!!!

I can't believe how hard it is to get an answer from some of you guys!
I've asked you twice now about supply voltage. I know you said 9V, but I commented on that earlier. Go back and read that before you answer. I can't tell you how to divide down your voltage until we settle on a supply voltage.

For a load, I would try an ordinary 110V bulb, in the range of maybe 50W to 200W. Try them and see how the pedaling effort is.

 

i am sorry if this is making you frustated , but i too am confused. I read your posts and still do not understand...
i dont know which supply voltage you are talking about and i do not know how will this effect what input the LM 3914 can take.
in this case what should power supply should i connect to the LM 3914???


The generator can output/supply 0-40V
The LM 3914 will sense the output from the generator.
i know the LM 3914 will need a separate supply votlage to operate. correct?
What supply voltage should i provide for the LM 3914 then? i thought I said 9V wal wart or i understood the 5 or 6V to reduce the stress correct? for typical application on the datasheet, it shows that they were using 6.8-18V.
Lets say we will go with your recommendation of 5 or 6V wal wart as the supply voltage.
Then what would be next...

 

As far as i know, you only need one power supply, which is the one for the LM3914.
The LED drivers are constant current. As an example, let's say you have the chip programmed to drive each LED with 10mA. The power dissipation of each ON LED driver will be (vcc-Vfwd)*10mA, where Vfwd is the LED forward voltage drop. If you are using bar mode, where as many as 10 LEDs can be on at once, then the maximum dissipation will be 10*(vcc-Vfwd)*10mA. Notice that the power dissipation goes up as vcc goes up. This is why a low value of vcc is good. Power dissipation translates to heating of the LM3914.
If you are using red LEDs, Vfwd≈2V. If you use a 9V supply, the LM3914 can dissipate in excess of 700mW. Not harmful, but you probably wouldn't want to touch it.
If you use a 5V supply, the max dissipation with the same LED scenario would only be a little over 300mW.
With a 5V supply, the maximum usable input signal is, conservatively, about 3.5V. (see fig. 12 in the datasheet). What supply voltage do you want to use?
If you choose 5V, this means you need to attenuate your generator output voltage so that 0-40V becomes 0-3.5V. You should also set the Rhi pin (6) to 3.5V. Do you need a full schematic to do this? if so, I can create one.

If you choose to use dot mode, you can get by with a higher supply voltage, because only one LED (and driver) is on at a time. The current requirements on the power supply are also reduced.

 

Just to think outside the box a bit: You know, you could use the digital I/O from the WattsView (is that the right device?) , convert it to analog and drive your LED bargraph that way.

But let's clarify what we have so far. The generator can supposedly output up to 40VDC and you showed you were able to approach that. For safe design, I might say it's possible to hit 50V. Ron has described why you might need to divide this down to, say, 3.5V for input to a LM3914 that is driven by a 5V supply. Your original idea of using a resistor voltage divider is just fine for this, and these can be small, cheap, high ohms resistors. Like 10K, 1/4 watt. They will carry very little current and dissipate very little power.

We have not chosen a load. Since your WattsView will easily give you the data you need to label your bargraph, I'd go back to recommending my old favorite - the lightbulb. Cheap, reliable, reasonably safe, visual feedback. What more could you want? Non-linearity won't be a huge problem because you can calibrate things easily. You'll want to play around a bit to find the right wattage.

Under load you'll never see 40V again, and you might be tempted to change your voltage divider. But a sudden disconnection of the load (e.g.. broken filament) would send the voltage up to the freewheeling peak voltage. I suppose you might use a zener diode - say 15V - to limit input into your voltage divider. This would allow you to increase the "sensitivity" while still protecting the input.

 

AWESOME!!! this is great! thank you Ron and Wayne!!!
it makes so much more sense now.
thank you so much for explaining the whole supply power and generator output.
basically i was worried about the what generator output the LM 3914.
So it is dependent on the supply power of the LM 3914
But i should have a low supply power which in turn i would have to attenuate our generator output. how can i attenuate the generator?
on the other post, i saw that I could use a zener diode or the voltage divider i was talking about. can i have the exact voltage divider schematic to show to my teammates?

also that digital io is a fantastic idea!!! i didnt even notice it or anything
just to show i have so much more to learn. i will contact them for further info on the commands,etc.

 

...can i have the exact voltage divider schematic to show to my teammates?

I can't draw easily right now but I think I can talk you thru it.

First, understand that a zener diode is used in the "reverse" direction to a normal diode, and spends most of its time NOT conducting any current. However, if the voltage across it exceeds the nominal value of the zener, it breaks down (reversibly) and conducts. With no protection, it might become a fuse and be destroyed. So you put a resistor in series with it to limit the maximum current thru the zener. Let's say we use a 15V zener (there are MANY values available) and a 5k Ω resistor. With 50V from the generator applied to the 5k resistor-to-zener-to-ground arrangement, there will be 15 volts dropped across the zener and 35 volts across the resistor (sum = 50V). 35 volts over 5k = 7mA max current. So as long as the zener is rated well above 7mA, it would be safe in this arrangement.

Note that for ANY generator voltage over 15V, the voltage on top the zener is held to a constant 15V. The voltage there would only fall into measurement range when the generator voltage is below 15V, which might be fine under a real load. I recently put a 27V zener in a TV, so again there are many values available and you might experiment a bit to find out how much range you actually need for your load. Maybe it would take king kong to go over 10V if the load is big enough, and in this case your entire measurement range would be between 0 and 10 volts. You could use a 10V zener.

Now you're resistor voltage divider just needs to divide down whatever voltage is on top the zener, i.e. from 15V down to 3.5. The incoming voltage will never go off scale and damage the LM3914. The resistors in the divider should be "large" compared to the current limiting resistor on the zener, say 50k and up, so that they introduce minimal error.

 

great thanks!!!
as for the connecting the wattview board,
how would this zener diode affect it?
where would i connect the zener diode? right before the load and connect the wattsview before the zener diode correct? i dont know where to connect to get correct reading of wattage.

as for the load, i will try some light bulbs or led strip

I hope they email me back soon.
or my team and I will use labview to communicate and have it use the wattage and at certain increments drive and light up the LEDs one by one
you think this will work?

 

anyone know how to use labview to configure it to output from the digital io???
i called the support but they want to charge us $75 an hour and the person said it might take him 3-5hours -_-
i just want to take the already calculated watts data and do some cases/conditions on when each port will output to light the LED

 

...as for the connecting the wattview board,
how would this zener diode affect it?

If you were connecting directly to the generator for a voltage measurement before, "upstream" of the current-limiting resistor (5k in example), there will be no change.

...i dont know where to connect to get correct reading of wattage.

I guess the documentation for your board should describe this.

..or my team and I will use labview to communicate and have it use the wattage and at certain increments drive and light up the LEDs one by one
you think this will work?

This could definitely be made to work, but Labview is software, and you'd still need a piece of hardware that the computer can talk to, perhaps over USB, to control anything. I personally have a LabJack U3 HV and it's great for this sort of thing. It's for data acquisition but also supports quite a lot of output options including, for instance, PWM or pulse-width modulation to control LED brightness. You wouldn't need the WattsView if you had a more versatile device like the LabJack. Just sayin'. That said, I think you could find a single chip IC to convert the 8-bit digital signal from the WattsView to an analog voltage.

As you see, you have options and there are many ways to accomplish the same thing.

 

i guess the wattsview is using the serial port now.
im not sure if it can communicate this way.
i downloaded the wattsview driver from the site.
when i talked to support they said it would power the LEDs.
and people have already asked for similar customized programs.