Electronic Die

The simplicity of a
traditional die makes it exceptionally difficult to create a fully
equivalent electronic version, if only because an electronic version
requires a power supply and a collection of electronic components that
occupy a much larger volume than a normal die. This article describes an
electronic die that can be built using normal components or SMDs
as desired, and which comes very close to having the same format as a
traditional die in the latter case. Despite its simplicity, this
electronic die incorporates several interesting features. For instance,
the range of ‘spots’ can be increased from 1–6 to 0–9 using a jumper,
and it has standby function that disables the display approximately 8
seconds after the die has been ‘thrown’, in order to save energy.

The electronic die also uses energy efficiently by driving the
display in pulsed mode. As a result of the latter two features, the
current consumption of the circuit is approximately 25 mA in use and 12
mA in standby. This means that it can easily be powered by a 9-V
battery. The circuit consists of the following parts: a free-running
oscillator (IC1a), additional logic for driving the display (IC1c &
IC1d), a timer (IC1b), a counter (IC3) and a display decoder (IC2). The
oscillator is very simple. Its frequency, which is determined by R1 and
C1, is approximately 225 Hz, with a duty cycle of around 50–60 percent.
The signal from the oscillator acts as a clock signal for the counter
(via R2) and a blanking signal for the display decoder (via IC1d).

However, the counter will not count as long as the ‘throw’ switch
(S1) remains closed, since the clock input of IC3 is grounded by S1. The
blanking input of the display decoder is driven by a pulse waveform, so
the display is in principle illuminated only around 50 percent of the
time, but it appears to be constantly illuminated due to the high clock
frequency. The standby mode works as follows. As long as there is a
signal on the clock input of the counter (S1 pressed), the output of
gate IC1b is low and the display is enabled. If S1 is released, the
counter stops and a number will be shown on the display. However, the
clock pulses will have charged C2 via D1, and C2 will slowly discharge
via R4.

After approximately 8 seconds, the output of gate IC1b will go high,
causing the display to be blanked. The design of the counter is
relatively simple. It is wired as an up counter by connecting the U/D
pin to VCC. The preset inputs (pins 4, 12, 13
and 3) are configured to binary ‘0001’, and the counter normally has a
counting range of 0–9 (pin 9 connected to ground). Diodes D2, D3 and D4,
in combination with resistor R5, act as a logic AND
gate, so if the value of the counter is greater than 6, the preset
value of 1 is latched into the counter and it starts to count again from
1 to 6. This only happens if jumper J1 is open. If it is closed, the
preset pulse on PREN is suppressed and the
counter range is 0–9. The A, B, C and D inputs of the decoder IC (IC2)
are driven directly by the counter.

The series resistors normally used for the individual segments of
the display are instead placed in the common-cathode lead (R7 & R8).
This has the advantage of allowing the number of resistors to be
reduced, although it has the drawback that the brightness of the display
depends on the displayed number. If the segment current is sufficiently
large, (light) saturation occurs and this brightness variation is no
longer noticeable. The Blank input (BL) controls whether the display is
enabled. If you choose to build this circuit using SMD technology, that will not affect the schematic diagram, but it will naturally affect the choice of components. In this case, SMD
components must be used for the resistors and C1, the diodes must be
replaced by BAS32 types, and BT versions of ICs IC1–IC3 must be used
instead of conventional types.

An SMD version of C2 was not used in the prototype, since SMD
electrolytic capacitors are expensive, and normally they are only sold
in lots of 10, just like other passive components. It is also
recommended to use a socket for the display of the SMD
version of the electronic die, to allow the space under the display to
also be used and the dimensions of the circuit board to be further
reduced. Any desired DC power source providing a voltage of 5 to 15 V
can be used as a power supply. Due to the low current consumption of the
circuit, a 9-V battery will last quite a long time.

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