Turtle Sense communications board v.0.25a

Circuit Description for Turtle Sense v.0.25a

Turtle Sense v.0.25a is the Comm (communication) Board which connects to the remote Smart Sensor Board and to the piggybacked Phone Board. The Comm Board is powered from a separate battery pack of 8 AA rechargeable Eneloop batteries.

The battery pack is about 11V fully charged and has a capacity of 2 amp-hours. The positive battery input to the board first passes through a diode (D1) which protects the circuit from damage if a battery pack is somehow connected backwards. The battery voltage is filtered by two capacitors, C7 and C1. The battery level is monitored by a resistor divider R11 and R12. The voltage on R12 (BattMon) is measured by an analog to digital converter, or ADC, in the microprocessor. The battery pack powers two power supplies on the board: (1) a 3.3V linear low power voltage regulator (U3) which powers the microprocessor (U1) and related circuitry on the board; and (2) a 5.0V switching voltage regulator (U4) which powers the Phone Board. The 3.3V regulator U3 is on at all times, and its output is filtered by capacitors C17 and C5. The higher powered 5.0V regulator U4 is only turned on when the phone board is needed, in order to conserve battery power. Its output is filtered by L1 and C12. R15 and R16 set the voltage at 5.0V. C9, C10, C11, and R17 are used for proper operation of regulator U4. U4 is turned on by positive signal (PhnPower) from the microprocessor U1.

The microprocessor (U1) does lots of stuff inside its tiny little chip. You don't want to know about it. Really. Its program is very, very complicated, and was written by Sam.