Teatimer
by Martin Clausen (mc AT rotgradpsi DOT de)
This is a short time timer made with an AT89CX051. It is supporting times from 1 minute to 12 minutes.
You have been a lazy bone and now you have to work all night. So there is a need for strong tea. You start to make the tea, but you forget the time and it tastes: brrrr ...
Table of contents:
Simply press a key and the selected time is running. At the start it makes one beep, after the selected time there are three beeps.
The start button is effectively a reset button, because the AT89CX051 can not weak up from power down. After reset the MCU reads the status of the input pins to determ the requested time. The common connection of the jumpers is pulled low to read only. A permanent connection to ground would cause a relatively huge current flow all the time because of the pull up resistor inside the MCU. A beep is performed to show activity. According to the jumper setting the number of cyles for this time is determed. A cycle is the time, that is necassary for Timer 0 to roll over, while working as a 13 stages counter. At 32KHz 20 cycles are one minute. During each cycle the MCU first flashes an LED (optional) and then goes into idel mode to reduce power consumption (about 0.33mW at 3V). Only Timer 0 and the oscillator are running. After all necassary cycles three beeps are performed and the MCU enters power down mode until the next reset.
- Semiconductors:
- 1 AT89C1051 or AT89C2051; see also programming tips
- 1 red low current LED
Capacitors:
- 1 68pF cer
- 1 100nF cer
- 1 1µF
- 1 10µF
Resistors:
- 1 560
- 1 10k
- 2 100k
- 1 330k
Mechanic:
- 1 case
- 1 pbc
- 1 some thin wire
- 1 socket 20 pin
- 1 switch
- 1 battery, 3V, Li
- 1 32,678 KHz crystal
- 1 piezo
The part description in schematics is read as follows:
part type + value in exponential form + package description + subpart number in package
for example: C1040805,1 means Capacitor, 100nF, package SMD 0805, first subpart in package
Disclaimer: No warranty at all!
Copyright by Martin Clausen, Germany.
Contact the author: mc AT rotgradpsi DOT de
Impressum
