Builda digital clock that turns AC load on/off with preset time. 
sourcecode with sdcc for 8051.
The Clock Controller V1.1was designed to be an exemplary of using ‘C’ language to control timer0interrupt, 7-segment LED and keypad scanning. It provides 1-bit sink currentdriving output, for driving a relay, opto-triac, say. Many projects requiring7-segment display and keypad interfacing may get the idea from the Clockcircuit and software.
Hardware
Figure 1 shows a circuitdiagram of the Clock Controller V1.1. P10-P1.7 drives 7-segment commonanode LED with sink current. P3.0-P3.3 also drives a base pin of 4-PNPtransistor, 2n2907 with sink current. As shown in the figure, the 2nd 2-digitLED that connected to P3.2 and P3.3 is rotated 180 degrees to the 1st 2-digitallowing the pt. segment to be used for 1 second blinking. P3.0-P3.3 alsoconnects four momentary switches while the other legs are tied to inputport P3.4. During display and key switch scanning, a logic ‘0’ is shiftedfrom P3.0 to P3.3, if there was a key pressed, P3.4 then became low.P3.7 is a 1-bit sink current driving, an example in the circuit uses a2n2907 to drive a small electromechanical relay 5V, say.\
Software
The program clock.cwas written in ‘C’ language and was complied by Micro-C Compiler from DunfiledDevelopment Systems. The memory model is TINY. The hex file of clock.csuitable for downloading by Easy-Downloaderis clock.hex.
The Clock1.cwas modified for C51 compiler. The function that updates real-time clockwas moved into timer0 interrupt service routine. The HEX file is Clock1.hexsmaller than compiled by Micro-C.
I got many requests askingmodification of the source code. Now you can modify the source code byyourself with the free compiler sdcc for 8051. Here is the source codeof new firmware, clock2.c and the hex file, clock2.hex.Please test it and let me know the result. I haven’t tested my hardwareyet, because I cannot find it now. This project is quite long time ago.You may add your code or modify whatever you like to have using sdcc! Youmay download the sdcc here, sdcc.zip.
For more detail: Clock ControllerV1.1 using AT89C2051
