Editing Monolog (section)

==Analogue board==
The analogue board provides the interface circuitry between the monitored and control telephone lines and the microprocessor. The board contains the following ICs;

* U1 = OP490 - Quad [[op-amp]]
* U2 = Mitel MT8870CE - [[DTMF]] decoder
* U3 = Motorola MC145442 - Single-chip V.21 300-Baud modem
* U4 = [[LM358N]] - Dual low power op-amp
* U5 = Phillips [[74HC157]] - Quad 2-input [[multiplexer]]

The board also contain a 25-way female [[D connector|D-type connector]] that provides the electrical interface to the monitored/control lines. Alternatively, it provides an [[RS-232]] interface thereby enabling the direct connection of a PC running the ''Dialog'' software.

===Battery charging circuit===
Monolog's batteries can be charged via two  spare pins on the 25-way D-type connector; pin 4 (RTS) and pin 20 (DTR). If a 12volt power source is applied to either pin, the batteries are charged at 22 mA. If both pins are used, the batteries are charged at 44 mA. The 12 volt feed is via two 330 Ω current limiting resistors and the wired in fuse. This circuitry does not provide any protection against over-charging.