16 Stage Bi-Directional LED Sequencer
The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516)
and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the
popular "Night Rider" display. A Schmitt Trigger oscillator provides
the clock signal for the counter and the rate can be adjusted with the
500K pot. Two additional Schmitt Trigger inverters are used as a SET/RESET
latch to control the counting direction (up or down). Be sure to use the
74HC14 and not the 74HCT14, the 74HCT14 may not work due to the low
TTL input trigger level. When the highest count is reached (1111) the
low output at pin 7 sets the latch so that the UP/DOWN input to the counter
goes low and causes the counter to begin decrementing. When the lowest
count is reached (0000) the latch is reset (high) so that the counter will
begin incrementing on the next rising clock edge. The three lowest counter
bits (Q0, Q1, Q2) are connected to both decoders in parallel and the highest
bit Q3 is used to select the appropriate decoder. The circuit can be used to
drive 12 volt/25 watt lamps with the addition of two transistors per lamp as
shown below in the section below titled "Interfacing 5 volt CMOS to 12 volt
loads"
Interfacing 5 volt CMOS to 12 volt/ 25 Watt Loads
The circuit below is designed to be used with the bi-directional lamp
sequencer shown above on this same page. Two additional transistors are
used to increase the current from the 74HCT138 decoder to control 12 volt
25 watt lamps. A 6.8 volt/1 watt zener diode is used in series with the
ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s)
so that the total voltage across the CMOS devices will be about 5.2 volts
and the outputs will move from +12 to about +7 when selected. The 2N2905/PNP
transistor stage is connected as an emitter follower which provides a high
impedance to the decoder output and supplies about 80 mA of current to the
base of the 2N3055 NPN power transistor which then supplies 2 or more amps
to the 12 volt lamp. The voltage across the PNP transistor will be about
7 volts when it is turned on and the heat dissapation will be about 0.6 watts.
That should't require a heat sink if several lamps are sequencing
but it may get quite warm if the circuit is idle on a single output.
The 2N3055 power transistor operates as a switch and drops very little
voltage (less than 0.5) when conducting, and will not require a heat
sink. Other transistors may be substituted such as the TIP29 or TIP31
for the 2N3055 and most any medium power (500mA) PNP for the 2N2905.
Expandable 16 Stage LED Sequencer
The circuit below uses a hex Schmitt Trigger inverter (74HC14) and
two 8 bit Serial-In/Parallel-Out shift registers (74HCT164 or 74HC164) to
sequence 16 LEDs. The circuit can be expanded to greater lengths by cascading
additional shift registers and connecting the 8th output (pin 13) to the data
input (pin 1) of the succeeding stage. A Schmitt trigger oscillator
(74HC14 pin 1 and 2) produces the clock signal for the shift registers,
the rate being approximately 1/RC. Two additional Schmitt Trigger stages
are used to reset and load the registers when power is turned on. Timing
is not critical, however the output at pin 8 of the Schmitt Trigger must
remain high during the first LOW to HIGH clock transition at pin 8 of the
registers, and must return low before the second rising edge to load a
single bit. If the clock rate is increased, the length of the signal at pin
9 of the Schmitt Trigger should be reduced proportionally to avoid loading
more than one bit. The HCT devices will normally provide about 4 mA
(source or sink) from each output but can supply greater currents
(possibly 25 mA) if only one output is loaded. The common 150 ohm resistor
restricts the current below 25 mA using a 6 volt power source. If the
circuit is operated with two or more LEDs on at the same time, resistors
may be needed in series with each LED to avoid exceeding the maximum total
output current for each IC of 25 mA. For greater brightness, individual
buffer transistors can be used as shown in the 10 stage LED sequencer on
this same page.
10 Channel LED Sequencer
Two Transistor LED Flasher
Fading Red Eyes
This circuit can be used to slowly illuminate and fade a pair of red LEDs. A linear 3 volt p-p ramping wavform is generated at pin 1 of the IC and buffered with an emitter follower transistor stage. The 22uF capacitor and 47K resistor connected to pin 2 establish the frequency which is about 0.5 Hz.
28 LED Clock Timer
This is a programmable clock timer circuit that uses individual LEDs to indicate hours and minutes. 12 LEDs can be arranged in a circle to represent the 12 hours of a clock face and an additional 12 LEDs can be arranged in an outer circle to indicate 5 minute intervals within the hour. 4 additional LEDs are used to indicate 1 to 4 minutes of time within each 5 minute interval.
The circuit is powered from a small 12.6 volt center tapped line transformer and the 60 cycle line frequency is used for the time base. The transformer is connected in a full wave, center tapped configuration which produces about 8.5 volts unregulated DC. A 47 ohm resistor and 5.1 volt, 1 watt zener regulate the supply for the 74HCT circuits.
A 14 stage 74HCT4020 binary counter and two NAND gates are used to divide the line frequency by 3600 producing a one minute pulse which is used to reset the counter and advance the 4017 decade counter. The decade counter counts the minutes from 0 to 4 and resets on the fifth count or every 5 minutes which advances one section of a dual 4 bit binary counter (74HCT393). The 4 bits of this counter are then decoded into one of 12 outputs by two 74HCT138 (3 line to 8 line) decoder circuits. The most significant bit is used in conjunction with an inverter to select the appropriate decoder. During the first eight counts, the low state of the MSB is inverted to supply a high level to enable the decoder that drives the first 8 LEDs. During counts 9 to 12, the MSB will be high and will select the decoder that drives the remaining 4 LEDs while disabling the other decoder. The decoded outputs are low when selected and the 12 LEDs are connected common anode with a 330 ohm current limiting resistor to the +5 volt supply. The 5th output of the second decoder (pin 11) is used to reset the binary counter so that it counts to 11 and then resets to zero on the 12th count. A high reset level is required for the 393 counters, so the low output from the last decoder stage (pin 11) is inverted with one section of a 74HCT14 hex Schmitt trigger inverter circuit. A 10K resistor and 0.1uF cap are used to extend the reset time, ensuring the counter receives a reset signal which is much longer than the minimum time required. The reset signal is also connected to the clock input (pin 13) of the second 4 bit counter (1/2 74HCT393) which advances the hour LEDs and resets on the 12th hour in a similar manner.
Setting the correct time is accomplished with two manual push buttons which feed the Q4 stage (pin 7) of the 4020 counter to the minute and hour reset circuits which advance the counters at 3.75 counts per second. A slower rate can be obtained by using the Q5 or Q6 stages. For test purposes, you can use Q1 (pin 9) which will advance the minutes at 30 per second.
The time interval circuit (shown below the clock) consists of a SET/RESET flipflop made from the two remaining NAND gates (74HCT00). The desired time interval is programmed by connecting the anodes of the six diodes labeled start, stop and AM/PM to the appropriate decoder outputs. For example, to turn the relay on at 7:05AM and turn it off at 8:05AM, you would connect one of the diodes from the start section to the cathode of the LED that represents 7 hours, the second diode to the LED cathode that represents 5 minutes and the third diode to the AM line of the CD4013. The stop time is programmed in the same manner. Two additional push buttons are used to manually open and close the relay. The low start and stop signals at the common cathode connections are capacitively coupled to the NAND gates so that the manual push buttons can override the 5 minute time duration. That way, you can immediately reset the relay without waiting 5 minutes for the start signal to go away.
The two power supply rectifier diodes are 1N400X variety and the switching diodes are 1N914 or 4148s but any general purpose diodes can be used. 0.1 uF caps (not shown on schematic) may be needed near the power pins of each IC. All parts should be available from Radio Shack with the exception of the 74HCT4017 decade counter which I didn't see listed. You can use either 74HC or 74HCT parts, the only difference between the two is that the input switching levels of the HCT devices are compatible with worst case TTL logic outputs. The HC device inputs are set at 50% of Vcc, so they may not work when driven from marginal TTL logic outputs. You can use a regular 4017 in place of the 74HCT4017 but the output current will much lower (less than 1 mA) and 4 additional transistors will be required to drive the LEDs. Without the buffer transistors, you can use a 10K resistor in place of the 330 and the LEDs will be visible, but very dim. Using the 4017 to drive LEDs with transistor buffers is shown in the "10 Channel LED Sequencer" at the top of this page.
Time Interval Relay Circuit
for the clock circuit above
72 LED Clock
In the circuit below, 60 individual LEDs are used to indicate the minutes of a clock and 12 LEDs indicate hours. The power supply and time base circuitry is the same as described in the 28 LED clock circuit above. The minutes section of the clock is comprised of eight 74HCT164 shift registers cascaded so that a single bit can be recirculated through the 60 stages indicating the appropriate minute of the hour. Only two of the minutes shift registers are shown connected to 16 LEDs. Pin 13 of each register connects to pin 1 of the next for 7 registers. Pin 6 of the 8th register should connect back to pin 1 of the first register using the 47K resistor. Pins 2,9,8, 14 and 7 of all 8 minutes registers (74HC164) should be connected in parallel (pin 8 to pin 8, pin 9 to pin 9, etc.). The hours section contains two 8 bit shift registers and works the same way as the minutes to display 1 of 12 hours. Pin 9 of all 74HCT164s (hours and minutes) should be connected together. For 50 Hertz operation, the time base section of the circuit can be modified as shown in the lower drawing labeled "50 Hertz LED Clock Time Base". You will need an extra IC (74HC30) to do this since it requires decoding 7 bits of the counter instead of 4. The two dual input NAND gates (1/2 74HC00) that are not used in the 50 Hertz modification should have their inputs connected to ground.
When power is applied, a single "1" bit is loaded into the first stage of both the minutes and hours registers. To accomplish this, a momentary low reset signal is sent to all the registers (at pin 9) and also a NAND gate to lock out any clock transitions at pin 8 of the minutes registers. At the same time, a high level is applied to the data input lines of both minutes and hours registers at pin 1. A single positive going clock pulse (at pin 8) is generated at the end of the reset signal which loads a high level into the first stage of the minutes register. The rising edge of first stage output at pin 3 advances the hours (at pin 8) and a single bit is also loaded into the hours register. Power should remain off for about 3 seconds or more before being re-applied to allow the filter and timing capacitors to discharge. A 1K bleeder resistor is used across the 1000uF filter capacitor to discharge it in about 3 seconds. The timing diagram illustrates the power-on sequence where T1 is the time power is applied and beginning of the reset signal, T2 is the end of the reset signal, T3 is the clock signal to move a high level at pin 1 into the first register, T4 is the end of the data signal. The time delay from T2 to T3 is exaggerated in the drawing and is actually a very short time of just the propagation delay through the inverter and gate.
Two momentary push buttons can be used to set the correct time. The button labeled "M" will increment the minutes slowly and the one labled "H" much faster so that the hours increment slowly. The hours should be set first, followed by minutes.
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50 Hertz LED Clock Timebase
