This is a doorbell. Well, a special one: it plays samples. You can use it for
"ding-dong" or "continuous-ringing". That's it.
OK, some more words. The doorbell uses an 8751 microcontroller, this is the
standard 8051 with EPROM code memory. Accompanied with a 128 KByte flash
EEPROM, a digital-analog-converter, and an amplifier, it works as an
"electronic acoustic notification system".
Its features are:
- Powered by 230 V mains, consumption reduced to minimum while idle.
- Triggered by standard bell voltages about 6V and above, DC or AC.
- Usual speakers can be used, 10 W max.
- Sounds are 8000 samples per second, 8 bits per sample.
- Configurable for single or continuous playing while the bell key is
- Programming via serial interface, 9600 8-N-1.
- Fail-safe sounds in case of empty or defective memory.
klingel_v1_4.zip Archive with schematic,
source, binary, documentation, example sounds, 111KB.
This is one of my most successful projects. The hardware was built early in
1996, and it worked well for many years until I sold my flat. It may be still
in use today because the new owners liked it very much. Some software updates
were seen, but nothing was seriously wrong.
There are some hardware changes, compared with the schematic:
- U8 pin 16 has to be connected to V12.
- All pins of port 0 (U1 pins 32 to 39) are pulled up to VCC by resistors of
- Port 2 bit 5 got a pull-up resistor to VCC of 4k7.
- The flash EEPROM needs 2 capacitors of 100n between VCC and GND, and V12
and GND, respectively.
- The value of C9 was reduced to 4u7.
- Between '+' and '-' of D2 (the bridge rectifier for the bell signal) a
capacitor of 1u0, 35V was added.
Since I don't have any more use of the paperwork, I'd love to give it away in
compensation of the postage. For just few bucks you'll receive printed:
- bill of material,
- layout plot (this is the most valuable page, as you can make a
circuit board with it!),
- assembly drawing,
- drill film,
- copy of the datasheet of the relais,
- and copy of the datasheet of the amplifier.
Who to blame:
Back to my home page.
Comments and such stuff go to: firstname.lastname@example.org