Bugler
Yes it's loud.
In a Scout troop, bugle calls are used to communicate messages to a large number of people over a large area. Unfortunately, not every troop has a scout which can play the bugle.
Enter the Bugler, affectionately called “the robot” by the scouts.
History
In 2005 I cobbled the first prototype (Hydra – because it has three 15W horns) out of an electrical box, a few Valcom paging horns my Dad had laying around, and part of a wrecked wagon.
The Bugler was a huge hit and the scouts loved it.
In 2006 I was commissioned by Dr. Dave Schimmel to build two additional Buglers for the Atlanta Area Council Green Bar Leadership Training Course.
In 2007 the buglers were serviced and the charging circuitry was overhauled. They have been in use since 2006. They have weathered storms, been left out overnight and abused by countless teenage boys for the last three years. They are still loud.
Design
The design is centered around the horn, a Valcom V-1038, a 30 Watt one way paging horn. The V-1038 requires 48V at 1A. Obviously, it had to be battery powered.
For cost and charging reasons, sealed lead acid batteries were selected. Unfortunately, of the SLAs I had only two 12V cells fit into the selected enclosure. To obtain the required 48VDC for the paging horn, I designed a switching DC-DC converter to generate 48VDC from 24VDC.
I also designed battery chargers to charge the SLAs. They are based on the Texas Instruments BQ2031. These chargers (as many other “intelligent” chargers) refuse to charge if the battery voltage is too low. In 2008, thinking that the chargers were faulty because they failed to charge completely flat batteries, the BQ2031 chargers were replaced with commercial chargers from EBay. These chargers unfortunately suffer the same problem that the homegrown chargers suffered from.
The best design would be to construct some sort of battery monitoring circuit which alerted the user if the battery voltage was too low. The work-around to this problem was to “jump” the pack with a “dumb” SLA charger common to auto repair shops (no more than a transformer, rectifier and resistor) and then use the intelligent charger built into the unit.