TIM 2015 Technical Manual v1 (February 2018)
Page 7
The audio is then passed to module
MOD5
(Mitel 88422-3), which connects it to a telephone line (in the same way as a telephone answering
machine answers a call). This module a
specialised telephone line interface
to handle the transmission of audio, call ringing detection and
line seize/release. It isolates the phone line voltage and provides logic-level control lines for the microcontroller to detect incoming calls
(ringing) and answer/release them.
The audio announcements are also sent via a
volume control
(R26) to an audio power amplifier module (
MOD6
). This contains a PAM8403
stereo 3-watt Class D amplifier IC that lets you hear the announcements on a loudspeaker for quality monitoring and testing. This PAM8403
chip uses digital audio processing to achieve an efficiency of up to 90%, resulting in much reduced power consumption. Only one audio
channel of the amplifier is used because the sound in TIM 2015 is mono (not stereo).
The volume control also incorporates a
switch output
, which is inverted by transistor T5 to place the PAM8403 chip into very low power
shutdown mode (consuming less than 1
µ
A) when the (switched) volume control is turned off. A separate part (IC3A) of the MC33072 op-
amp provides an audio output for headphones, monitoring, etc. and has its own volume preset (R20).
A 128x64-pixel, ST7920-type LCD module (QC12864B) is used for the
graphic display screen
. It uses a 3-wire serial SPI interface to
communicate with the microcontroller. Display brightness is controlled using a PWM output from the microcontroller to driver transistor
T3.
The
user interface
is provided by a mechanical rotary encoder (with switch). When it is turned between each detent it sends a series of logic
level pulses via the two wires (A and B). By analysing the phase of these pulse edges the microcontroller determines the turn direction.
Power
for the whole clock is provided by the 3-amp regulator module
MOD1
. This module contains an MP1584 switching regulator chip
running at around 1MHz for about 85% power efficiency with a 12V input. The high switching frequency should also reduce any EMI
interference that might otherwise degrade reception of radio time signal signals.
Transistor T4 periodically provides power to a small
3.3V regulator
(IC1) under the control of the microcontroller. This 3.3V supply is
needed for the Wi-Fi module (MOD2) or can alternatively be used by an externally connected GPS module.
The
Wi-Fi module
(
MOD2
) contains an ESP8266 processor that runs a program for handling the initial Wi-Fi configuration and then
periodically requesting the time from network servers. This Wi-Fi module uses a significant amount of power when active (about 200mA)
and although there is a low-power Sleep option, the module does not have the necessary Sleep pin connected to the header. This is resolved
by using transistor T4 to completely cut the 3.3V power when the module is not being used.
Communication
is handled by a serial 3.3V logic link to the microcontroller. The module is not 5V-tolerant, requiring resistors R17 and R18
to lower the microcontroller output 5V logic levels to prevent damage to the Wi-Fi chip. Optional 30-second and serial time data outputs are
Содержание TIM 2015
Страница 1: ...TIM 2015 Technical Manual v1 February 2018 Page 1 TIM 2015 Speaking Clock TECHNICAL MANUAL...
Страница 9: ...TIM 2015 Technical Manual v1 February 2018 Page 9 Board dimensions 140 x 85mm...
Страница 10: ...TIM 2015 Technical Manual v1 February 2018 Page 10 Board layout...
Страница 11: ...TIM 2015 Technical Manual v1 February 2018 Page 11 Circuit diagram...
