• AlarmClock
• Parts
• CL-B01

Part description

The heart of the alarm clock is an Atmel ATmega8535 microcontroller (MC). It is clocked at 11.0592 MHz to facilitate an RS-232 serial interface, should the need ever arise. Currently, this is not implemented, but the clock frequency would allow for easy timer configuration for the usual serial communication setup to link with personal computers or workstations.

For radio time synchronization, a DCF77 receiver module from Conrad Electronic, order code 641138, is used, which runs at a wide range of supply voltage, and has open-collector outputs for DCF pulse signals, both normal and inverted. Connection to an MC input pin therefore requires the use of a pullup resistor.

When not being received from DCF77, time is kept in a DS1307 real time clock (RTC) chip with I2C bus interface. This can be connected to the MC's TWI interface, which is essentially the same technology under another name. This bus is clocked at 100kHz in this device. The I2C bus also allows for easy extension at a later time, which is currently planned for an RGB LED controller yet to be developed.

An Anag Vision AV2040 module is used as a display. This is a 4 line, 20 character, backlit display module that can be connected through a 16-wire interface. However, if driven in 4-bit mode, it takes only 6 MC I/O pins which is an acceptable footprint. It would have been possible to also use an I2C interface here, but this display was the most readily available for me. Please note that even though the datasheet of AV2040 says it uses a KS0066 or compatible controller, an initialization sequence from the KS0073 is needed to enable 4-line display mode. KS0066 datasheet does not mention the "extended function" register that is listed for KS0073, however this module needs exactly that mode to enable all four display lines.

Revisions

CL-B01.02

Current development revision.

Images

Changes to previous revision

• Integrated CL-B02 (buzzer pulse circuit) and CL-B03 (RGB LED PWM controller) into CL-B01 main board.
• Therefore new external interfaces.

External interfaces, Rev.02

CL-B01.01

Current stable revision.

External interfaces, Rev.01

Images

CategoryElectronics

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