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Power delivery system


Two posts ago we discussed how solar panels work, and how they might integrate into the game function of delivering power to a set of LEDs (houses).  This time we'll talk about a more complete, fleshed out design for a power delivery system which includes both solar cells and a hand crank generator.

The Goals

Up until now, the goals of this system have not been absolutely fixed, because I'm in the process of understanding what can physically be done, and connecting reality with the game concepts itself.  It kind of forms a constantly interacting triangle of aggravation shown so innocently here.

However, I think we can now have some more defined goals for this power system:

1) To power the LEDs in the houses (needed to win the game), players must spend resources to purchase solar cells (which produce a constant, fixed trickle charge) or operate the hand crank generator for a fixed amount of time (which produces a one time, large input of energy.  Later, other voltage sources may be added to the game (wind generator, pico-hydro (???), etc.).  An energy storage device (a capacitor) is used to store the energy produced by the hand crank and solar cell and distribute it to the LEDs.

2.possiblity1) Each player's power generation and distribution systems are independent from one another.

2.possibility2) All players operate on a unified power generation distribution system.  Each time I charge the capacitor, we all benefit (all our lights stay on).  This options requires a lot more player interaction and has a variety of variations within it.

Design Description


(sorry, this picture is too small - click on it to get larger picture and zoom in)

The design above does not include absolutely all elements (there are some additional diodes and other things needed), but does cover the most critical elements of the circuit.

Design Considerations an Detail

1) We must have a way for players to generate "additional power" to the system - This could be implemented in several ways.  For example, it's possible that a player's power plant can light up 3 LEDs, but at 4 LEDs the power is insufficient and the lights turn off.  This meas the player needs to "upgrade" their power plant to achieve 4 LEDs (this is similar to Power Grid in function).  Another method is to add Joules (or, in other units, amp hours) to a capacitor using the hand crank generator by cranking the generator for a fixed amount of time (5 or 10 seconds).  In this way, the same charged capacitor will supply 1 LED for 10 minutes, 2 LEDs for 5 minutes, 3 LEDs for 2.5 minutes, etc because it has a fixed supply of energy supplied by the hand crank.  Now we have a time element in the game, which really adds a different dynamic.   The system above allows both options: the hand crank generator provides a fixed amount of Joules to the capacitor, while the solar panel supplies a constant voltage to the capacitor which may be enough to continuously operate 1 LED depending on the light level, but not many LEDs (3 or 4).

2) Supplying a safe, constant voltage and amperage to the LEDs - A big problem is that none of our voltage sources output a fixed voltage.  Look at the V - I curve for the hand crank and solar panel and you'll find that the voltage produced CHANGES depending on what the current flow is.  This is not like a normal battery, or you AC outlet, which always produce a constant voltage, regardless of what is hooked up to them (ie a 9V battery always produces exactly 9V - or at least very very close until it's almost completely discharged).  Because our goal is to drive LEDs which must operate over a very narrow voltage range (like ~1.8V for red LEDs) or else they will burn out, we need to convert these variable voltage sources into a constant voltage source.  This is done using the voltage regulator, which converts an input voltage into a fixed output voltage.  Let's assume we want a constant 1.8V output for our LEDs.  There are two options for the voltage regulator design: we can supply the voltage regulator a high voltage (higher than 1.8V) and it can drop the voltage to 1.8.  That's called a "buck" configuration.  Or, we can supply the voltage regulator a lower voltage (lower than 1.8V) and it can increase the voltage to 1.8V.  That's called the "boost" configuration.  For a variety of reasons, it's not yet quite clear which configuration is the right way to go, but clearly it's critical to equipment sizing (our voltage sources, capacitor, and voltage regulator will be quite different in the two cases!)

3) Cost should be minimized - For board games, even small costs have a huge impact on the final price - lower cost = better, so long as we're not sacrificing the game concept itself.

I used the open source circuit design program called gEDA (GPL Electronic Design Automation) which combines a schematics drawing tool with a PCB editor in one pretty good package (see for more details).  There are several configurations and resulting drawings, but the below is one example.  A printed circuit board (PCB) is required to place the voltage regulator, capacitor, connectors, diode, and push button and voltage display on.  In this example, there is one single PCB which all player's circuits are placed, but the circuits themselves operate independently (each person has their own capacitor, solar panel, LEDs etc.).  It's not perfect (believe me, I know) and it's a work in progress, but not a bad start.

(sorry, this picture is too small - click on it to get larger picture and zoom in)

Next Steps

The major components and then the entire circuit need to be tested.  Most of the components have been ordered and many are already in (thanks Digikey), and should have a chance to prototype them this week.  This will be important to see if there are any glaring errors and if our expected values match actual values.  I have a strong feeling that a buck configuration will be necessary, which will require a redesign of the crank generator which is no small feat.  Once I have a more finalized configuration, I'll also put up the gEDA schematic and parts list.

Unrelated but still fun...

Thanks Thingiverse!

And look at what else my friend and I made on the laser cutter this week - a Shoji tea candle lamp!  See for details.  As always the first one took a while, but I bet once you get the hang of it you could crank these puppies out.  Still waiting to put on the paper and clean off the soot left by the laser, but it's going to look nice when all done.

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