Part of my work involves teaching young people about renewable energy through practical workshops such as solar panel making.
In order to 'race against the sun' we have assembled a bike powered DC generator which has an output in the 12V range, 0-100w.
We would like to create a large visual display to show the power output.
This could either be numeric or just visual (e.g. a bar chart made up of LED ribbons like this)
My preference if for the second option as it could be made REALLY large scale.
My thinking is to use an Arduino to convert power measurements to an output that is addressed for a pre-defined power range (e.g.0-10w,10-20w etc), which can then drive an LED strip via a relay.
I would appreciate some guidance on what code could be used to trigger different outputs on the Arduino for the different power levels (e.g. 0-10, 10-20, 30-40 etc)
Alternatively any thoughts on the overall approach and if there could be simpler alternatives would be welcome.
@Dave in nj- thanks for the links. I want to try the 'bar graph' approach rather than numeric, but will look again at this if I can't work out how to write the code required.
You can use RGB LED strips with integrated controllers, so that the Arduino only has to provide the display information to the strips, while power comes from a separate supply. Everything else requires additional driver circuits.
an FET will do the same thing, for less and the reliability goes up and the power use goes down.
if you total your costs for your display with both LED strips and FET drivers
and compare to the addressable LED strips, the whole project cost should not be too great.
Driving LED's with an FET is about the simplest part of the project.
if the LED portion of the project is $32 for a 5 meter strip you can have 5 strips a meter long to give the bar-graph
if you have 60/meter, that means your display would have 60 levels.
for any other technology, you would need to get additional circuitry to get 60 levels.
at 1/2 meter strips, that would offer a wider display, but 30 levels. still very good resolution.
This should be fine for the dumb LED strip which draws about 0.5A per m.
However the addressable LED strip is rated at 90w for 5m. At 5v that is 18A in total, and 3.6A/m (peak).
As this is more than ULN200x could drive with all outputs paralleled, am I right in thinking that a FET like this would be required (it can drive up to 5A)
Hi,
Why not make a big meter movement with a servo?
Like this but if you balance the "needle" it could be any size, and use your artistic efforts on a really good meter scale.
Just curious.
As an educator, you understand the difference between voltage, current and power...
To measure power - there must be a load, so then your generator has output with the capability of V volts, and I current.
You must make this distinction for your students, otherwise they’ll think pedalling faster generates more power, whereas it really develops more available power at a constant current. (Assuming the generator voltage varies with speed.)
There’s slightly more to it, but this is an important point.
I would say yes in terms of the V=IR relationship, although there are depths that are beyond me.
The primary focus of our workshops isn't the physics per se, but the concept and practice of sustainability- although physics is of course the foundation for that.
As the power consumption of the display linked in my previous post is lower than the addressable LEDs, we were thinking to partly discharge the 12V battery to provide a load, although it won't be a linear relationship as the state of charge increases. A big variable resistor could be a useful addition.
Thanks for your wording, which will be useful in explaining the relationship between load and power.
One point about the addressable LEDs is your assuming that you're going to have them a 100% lit 100% of the time. There's no reason why you can't just lite one row of LEDs and have a lit row go up or down as the power changes
Another comment is a regular LED that is turned on and off can be turned on and off very fast so you think it is on. It's what we call POV for Persistence of vision and that is a way to greatly reduce the power consumed by an LED.
as for Oms's law, it only takes a few minutes to cover the basics.
And it will give a much deeper understanding to your students of power.
another point is that you could have a row of lights, screw in christmas tree lights, or refrigerator lights. and as your generated power increases, light another light. with the Arduino, you can display a numerical load value as well.
