The fountain in solar powered modes,
disassembled to see the components, and at the side of the pool
in line powered mode.
(click image for better view)
This is a solar powered microcontroller driven pool fountain. It
was designed to provide an entertaining, pleasant visual and audible
water effect in a cordless low-maintainance device.
The basic hardware design has the following features:
- Low-voltage battery powered
- Solar charged (normally)
- Battery voltage sensing
- LED status indicator
- User controllable
- Dual ported water pump
12v NiCad battery
15V Solar cell
7805 Voltage regulator
Vero (strip) board
The parts are connected as depicted in this schematic.
Writing the software
was fun because of the challenge connecting the inputs (switch,
battery voltage) with the outputs (LED, water pump). Aside from
carrying out a water show, the software has to manage battery charging.
The charging circuitry is fairly primitive; connecting the solar-cell
to the battery through a diode to prevent discharge in low-light
conditions. Battery voltage is sensed through the voltage divider.
The CPU is responsible for preventing overcharging of the battery
and also for ensuring that deep-discharge doesn't occur, since both
of these conditions reduce battery-life substantially. To prevent
overcharging, the CPU turns on the pump if the battery voltage increases
above a predetermined value. Similarly, deep-discharge is avoided
by preventing the pump from turning on when the battery voltage
is below a certain level. Between the deep-discharge and overcharge
thresholds, the pump can be user controlled (via activation of the
reed switch). Battery voltage is indicated by an LED status light.
By making the pump activate according to battery voltage, the fountain
turns on only when user-activated or proportional to the battery
charging. On a sunny day with a single solar-cell, this amounts
to just a few times each hour. But with a 15v 1a wall wart supply
(to a GCFI outlet, of course!), water shows occur almost continuously.
Since current from the power supply exceeds the fast charge current
of the batteries, this is detrimental to the battery life, but can
be dealt with by 1) using a large battery pack which would allow
higher current recharging, 2) limiting the AC power supply current
to something more acceptable to the batteries, or 3) just disconnecting
the batteries when running on AC.
The fountain works well. However, using a linear regulator to drop
the supply voltage from 15v down to 5v results in a fairly high
standby current. In light of the low current draw of the 08M, this
is especially wasteful and drains the battery unnecessarily at night.
Packaging the device in a weatherproof, attractive, and practical
case was also more problematic then expected. The combination of
plastics that comprise the pump, tubing, electronic case, and baseboard,
presented problems when trying to find bonding agents to hold everything
together, but in a way that would allow disassembly if desired.
While I like hot-glue, it didn't stick well to certain components,
and also is likely to melt when heated by the sun on hot days.
The concept and hardware of this project were stimulated by thought
on a fountain design originally seen in Silicon Chip Online by Robert
Gatt. The source code presented here is completely fresh, well organized,
has various modes, and even has comments and multi-letter variables...
This code is explicitly released under the GPL.
And this page is licensed under a Creative
Commons Attribution 2.5 License.
Write me if you find this project
interesting. Link to this page if you find it relevant..
Warning, the sound of intermittent running water on a full stomach
of ice-tea may make render you socially unacceptable. This page
describes an electical project that is immersed in water, and in
the hands of a greenhorn (like you!) could lead to an untimely death
by electrocution. Lastly, this project is provided without any warranty
and probably isn't suitable for anything.
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