Turn a "c51 4bit clock" in a 24h timer
You can buy this clock for 1$ shipped on aliexpress and it works as expected, but you can not change the software. I've bought a pair of this clocks to turn them in a timer changing a little bit the code, but the cpu used is a 89c2051 with only parallel programming interface (the 89s2051 has a serial mode much easier to use) and I had no patience to put together such a device. The source code is not available and, to be honest, is pointless to mess with a 8051 cpu when you can get a much easier AVR and the Arduino IDE.
What is missing in this clock to turn it in a timer? It is really easy to hook a relais instead the beeper but there are some problems. First the default setup is horrible: it start, after a reset, at 12:59 with hourly chimes at 13:00, first alarm at 13:01 and second alarm at 13:02. Moreover every button click generates a beep.
The target are these two: remove the buttons beep and stop the default alarms.
Messing a little bit with the buttons I've discovered that, pressing Button1 at reset, the clock enter the programming mode and does not play the alarms.
So I need: -a circuit to force Button1 at reset to enter in programming mode -a circuit to mute the beeper on button click -a circuit to toggle a relais on regular alarms -a circuit to switch on and off the relais manually
C1 1 470uF C2 1 100uF C3,C4 2 2.2uF C5 1 1uF D1,D2,D3 3 1N4148 LED1 1 LED R1 1 1K R2,R4 2 390K R3,R5 2 10K R6 1 1.2M REL1 1 12V T1,T2 2 BC337 U1 1 4093 U2 1 4017 U3 1 LM7805
The hooking points to the original clock are:
The final assembly is:
At startup you have to program the two alarms to on/off the relais. Moreover you have to disable the hourly chimes.