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The classic concept of an hourglass taken into the modern world of electronics
Like the original antetype the electronic hourglass is started by turning it upside down. A nifty simulation of the grains of sand visualises the lapse of time and reacts naturally on the turning of the hourglass. If time has elapsed an optical alarm is issued. Depending on your needs you can implement more specific actions like pulling the tea bag out of your cup. The electronic hourglass excels on its antetype in the ability to adjust the time in intervals of 15 seconds.
You will need the usual tools for soldering electronic components. The microcontroller is an SMD type in a SO14 package. You will need the ability to solder SMD components. For soldering the controller it is best to use thin solder wire (0.5 mm) and tweezers.
Also for programming the microcontroller you need a suitable programmer (e. g. ARVisp MKII or USBasp). You should be familiar with flashing a microcontroller. If needed get instructions from the manufacturer of the programmer.
A kit is available that contains all of the above mentioned items except for the ribbon cable.
Operating the hourglass is pretty simple.
Once the hourglass has elapsed the current time setting is saved to EEPROM. This way the setting is preserved even when the Bits-of-Time are powered down.
The software is available on Github.
When the hourglass is started the upper bulb is filled with 54 grains of sand. According to the time setting these grains trickle down at a lower or higher rate.
The maximum time setting is defined by parameter MAX_MINUTES.
The microcontroller needs to be “flashed” (i. e. programmed) with the “Bits of Time” software. You will need a suitable programmer (e. g. ARVisp MKII or USBasp). First set the fuses in the controller to the values given by “fuses.txt”. Then write the file “Bits_of_Time.hex” to the microcontrollers flash memory.
Bits-of-Time uses the internal RC-oscillator of the microcontroller as a time base. Factory-provided the accuracy is 10 % or better. If you need a higher precision you have two options.
The output PA7 (CON5, pin 10) can provide a pulse-width modulation signal. PWM_MODE chooses between non-inverting and inverting modes. The prescaler setting (PWM_PRESCALER) defines the PWM frequency. With PWM_PRESCALER = 4 frequency is 61,3 Hz. This is suitable for controlling servo motors used in model making. On the PCB you have three solder pads with signals GND, Vdisplay and PA7 to which you can connect your servo.
The wodden box is only one of many possibilities.
“HorstKevinObst” has designed a very nifty 3D-printed case combining lightness with elegance. He has published his design on Thingiverse to share it with others.