Simple Project to Build A Very Useful Timed Beeper

Simple project to build, ideal for beginners! Timed Beeper: Beeps 7.5 seconds after a preset time, Adjustable time settings: 15s. 30s. 1min. & others

This circuit is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it is a modern substitute for the old sandglass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.

Very Useful Timed Beeper Circuit Diagram

Parts List:

R1 = 220R
R2 = 10M
R3 = 1M
R4 = 10K
R5 = 47K
C1 = 100nF-63V
C2 = 22µF-25V
D1 = 1N4148
D2 = 3mm. Red LED
Q1 = BC337
P1 = SPST Pushbutton (Start)
P2 = SPST Pushbutton (Reset)
PS = Piezo sounder (incorporating 3KHz oscillator)
B1 = 3V Battery (2 AA 1.5V Cells in series)
IC1 = CD4081 Quad 2 input AND Gate IC
IC2 = CD4060 14 stage ripple counter and oscillator IC
SW1 = 4 ways Switch (See notes)

Circuit operation:

Pushing on P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is around 4Hz. LED D2, driven by IC1A & B, flashing at the same oscillator frequency, will signal proper circuit operation. SW1 selects the appropriate pin of IC2 to adjust timing duration:

Position 1 = 15 seconds
Position 2 = 30 seconds
Position 3 = 1 minute
Position 4 = 2 minutes

When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push on P2.

Notes:

• SW1 can be any type of switch with the desired number of ways. If you want a single fixed timing duration, omit the switch and connect pins 9 & 13 of IC1 to the suitable pin of IC2.
• The circuit's reset is not immediate. Pushing P2 forces IC2 to oscillate very fast, but it takes some seconds to terminate the counting, especially if a high timer delay was chosen and the pushbutton is operated when the circuit was just starting. In order to speed the reset, try lowering the value of R5, but pay attention: too low a value can stop oscillation.
• Frequency operation varies with different brand names for IC2. E.g. Motorola's ICs run faster, therefore changing of C1 and/or R3 values may be necessary.
• You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
• An on-off switch is not provided because when off-state the circuit draws no significant current.

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CMOS Toggle Flip Flop Using Push Button

The circuit below uses a CMOS dual D flip flop (CD4013) to toggle a relay or other load with a momentary push button. Several push buttons can be wired in parallel to control the relay from multiple locations.A high level from the push button is coupled to the set line through a small (0.1uF) capacitor. The high level from the Q output is inverted by the upper transistor and supplies a low reset level to the reset line for about 400 mS, after which time the reset line returns to a high state and resets the flip flop. The lower flip flop section is configured for toggle operation and changes state on the rising edge of the clock line or at the same time as the upper flip flop moves to the set condition. The switch is debounced due to the short duration of the set signal relative to the long duration before the circuit is reset.

CMOS Toggle Flip Flop Using Push Button Circuit Diagram

 The Q or Qbar outputs will only supply about 2 mA of current, so a buffer transistor or power MOSFET is needed to drive a relay coil, or lamp, or other load. A 2N3904 or most any small signal NPN transistor can be used for relay coil resistances of 250 ohms or more. A 2N3053 or medium power (500 mA) transistor should be used for coil resistances below 250 ohms. The 47 ohm resistor and 10uF capacitor serve to decouple the circuit from the power supply and filter out any short duration noise signals that may be present. The RC network (.1/47K) at the SET line (pin 8) serves as a power-on reset to ensure the relay is denergized when circuit power is first applied. The reset idea was suggested by Terry Pinnell who used the circuit to control a shed light from multiple locations.

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Digital Clock Based on Sam Gordon Theory

The circuit was designed to implement the concept of Sam Gordon in making a digital clock with visible components from the viewer of the clock.

• Sam Clock – a digital clock equipment that is fully parametric or constantly varying with its parameters of function and construction, which has been operational for many years without problems on a 24 hour basis.
• 74HC – a quad 2-input NAND gate with standard output capability, and is high speed Si-gate CMOS device that is pin compatible with low power Schottky TTL and specified in compliance with JEDEC standard no. 7A.
• 74LS – a monolithic decade and binary counter that contains four master-slave flip flops and additional gating to provide a divide-by-two counter and a 3-stage binary counter with typical power dissipation of 45 mW and count frequency of 42 MHz.
• 4060 – a 14-bit ripple counter with internal oscillator that has glitches which may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.
• LM317 – an adjustable 3-terminal positive voltage regulator capable of supplying in excess of 1.5A over an output voltage range of 1.2V to 37V and requires only two external resistors to set the output voltage due to its internal current limiting, thermal shutdown and safe area compensation, making it essentially blow-out proof.
• 4017 – a decade counter where the count advances as the clock input becomes high that may be combined with diodes for some functions such as flash sequences.

The main clock circuit consists of TTL and several CMOS represented by IC9 to IC13. The component combination drives the common cathode LED display while common anode can be driven when CMOS 4511 is replaced with 74LS47. Changing from common cathode to common anode would require the change of connection in DIS1 up to DIS5 display. A 1 Hz pulse frequency that comes from SL10 is divided in sequence by IC2 and IC4 within the region of the gates to make sure the indication of time in the format of Hours, Minutes, and Seconds. The tens of Hours are driven by Q1 with only the LED B and C of DIS6 display to indicate 1 to 12 for Hours indication. A small heatsink may be used to suppress the increase in temperature of Q1.

The supplied voltage of the circuit is shared into two lines where the 5 VA supplied with voltage in case of breakdown in network voltage, supplies all the ICs except the IC9 to IC13 which is being supplied by 5 VB. A battery is alternatively used in the case of interruption of circuit voltage. The second figure shows the indication of the display as it is driven by IC9 to IC13 where CMOS 4511 is used. The diodes DIS1 to DIS5 are conducting as common cathode while DIS6 will always be common anode. The use of 74LS47 will cause the DIS1 to DIS5 to conduct at common anode with their pins 1 and 6 going to the line of 5 VB with R39 and R40 to 0 V line. The dot in DIS3 and DIS5 is turned ON by these resistors to produce a division of LED displays.

There are two ways, found in the initial startup of operation, by which the 1 Hz pulse can be produced which constitute to the basis of time for the clock. The two methods consist of using a crystal oscillator with high oscillation frequency and the division of this frequency to create 1 Hz in the end. This would ensure a very précised and stable operation in producing the pulses. The crystal oscillator in figure 3 produces the 1 MHz frequency that is divided in stages from the IC15 up to IC17.

The gates A and B of IC18 and IC19 are not initially included in the operation unless the switches S1 or S2 are pressed to modify the time. Pressing the Super Fast (S1), would release a frequency pulse of 10 KHz while pressing Fast (S2) would release a pulse frequency of 100 Hz, to show indication to the display concerning the modification of time in a short interval. The figure 3 circuit is being supplied by 5 VA where the operation of oscillator is ensured, even in the event of voltage interruption, which would trigger the use of the battery.

Figure 4 also introduced the usage of crystal oscillator to produce 1 Hz in the output of SL19. This frequency is made possible by successive division 3.2768 MHz frequency coming from the oscillator, in the start of the operation. The presence of variable capacitor C3 is for altering the oscillator in order to test the frequency pulse at 204800 Hz. The indication of display is regulated by the switches S1 (fast) and S2 (super fast) for having a frequency of 10 Hz and 100 Hz respectively. The adjustment of time will be in a short interval, since the indication of display runs very fast. The use of mechanic switches is preferred due to simplicity. The circuit is similarly powered as in figure 3.

The fifth figure shows the power supply as it provides the necessary voltage for the operation of the circuit, together with the charging mechanism for the battery and the transfer in battery during voltage interruptions. The output from this supply circuit is regulated by the trimmer TR1 to produce 5 V at P1 to enable the functionality of the circuit. The next trimmer TR2 regulates IC25 as it gives 6.9 V at P2, which charges the lead acid battery which is rated 6V per 1 Ah, connected to SL17. During voltage interruption, the relay RL1 is triggered where its contacts connect the 5 VA line to the 6 V battery via the D5 and D6while 5 VB is connected to 0 V where the display stops.

The duration by which the contacts transfer from one state to the other is determined by C17. The IC24 and IC25 should be placed in a heatsink and be regulated with TR1 and TR2 without being connected to the supply circuit except during the use of batteries.The concept of the circuit is also embraced in other digital clocks. And because they are small inexpensive devices with LED displays, they are typically found in automobile clocks, desk clocks, microwave ovens, industrial clocks, computers, interval timers, radios, and televisions.

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24 Second Shot Clock

This is a circuit intended to be used in basketball shot clock. To start in 24 seconds; 24s LOAD SW and Reset SW should be push simultaneously. If not, the count will start in 99. Pulse input can be connected to 555 astable multivibrator but must be calibrated for real time clock. The PAUSE SW must have a Switch Debouncer so that the counter will count normal when counting is paused and then turn-on.

24 Second Shot Clock Circuit Diagram

When the count reach 00, the NOR gate will have an output of logic1 that will turn on the two transistor. The buzzer will rung and light will turn on. The two transistors are continuously turn-on not until LOAD SW and Reset SW is push. All have a +5v power supply.

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Binary Coded Decimal (BCD) Clock

The clock circuit above uses seven ICs and 19 LEDs to indicate binary coded decimal time. The LEDs can be arranged (as shown in example above) so that each horizontal group of 3 or 4 LEDs represents a decimal digit between 0 and 9 and each individual LED represents a single bit or (binary digit) of the value. Binary digits have only two values (0 and 1) so a number written in binary would be something like 1001 or 0011, which represents decimal numbers 9 and 3 respectively. From right to left, each binary (1) represents increasing powers of 2, so that a 1 in the right hand place represents 2^0=1 and the next place to the left is 2^1=2 and then 2^2=4, and so forth.


This makes binary counting fairly easy since each digit has a value of twice the one before or 1,2,4,8,16,32,64,etc. Thus the decimal value can be found by simply adding the values of each illuminated LED in the same row, (the total is shown in the box to the right). For example, the binary number 1001 would have a decimal value of 8+0+0+1 = 9. But this is actually a binary coded decimal 9 since only values from 0 to 9 are used 0000 to 1001. A true binary clock indicating minutes of the hour would display values from 0 to 59, or 000000 to 111011. But this would be more difficult to read since adding values 32 + 16 + 8 + 2 + 1 = 59 is not as easy as 8 + 0 + 0 + 1 = 9.

The circuit is powered by a small 12.6 VAC transformer which also provides a low voltage 60 Hz signal for a very accurate time base. The transformer is connected with the secondary center tap at ground which produces about 8 volts DC across the 3300uF filter capacitor. DC power for the circuit is regulated at about 5.5 using a NPN transistor (2N3053) and 6.2 volt zener diode. The 2N3053 gets a little warm when several LEDs are on, and may require a little (top hat type) heat sink.
 
Binary Coded Decimal (BCD) Clock Circuit Diagram:

A one second clock pulse is obtained by counting 60 cycles of the AC line signal. This is accomplished using a CMOS CD4040 12 stage binary counter (shown in light blue). The 60th count is detected by the two NAND gates connected to pins 2,3,5,and 6 of the counter. When all four of these lines are high, the count will be 60 resulting in a high level at pin 4 of the 74HC14 which resets the counter to zero and advances the seconds counter (74HC390 shown in purple) when pin 4 returns to a low state.

The same process is used to detect 60 seconds and 60 minutes to reset the counters and advance the minutes and hours counters respectively. In both of these cases the 2 and 4 bit lines of the tens counter section will be high (20+40=60). In all three cases (seconds, minutes and hours) a combination 10K resistor and 0.1uF capacitor is used at the input to the 74HC14 inverter to extend the pulse width to about 300uS so the counters will reliably reset. Without the RC parts, the reset pulse may not be long enough to reset all stages of the counter since as soon as the first bit resets, the inputs to the NAND gate will no longer all be high and the reset pulse will end. Adding the RC parts eliminates that possibility.

The reset process for the hours is a little different since for a 12 hour clock we need to reset the hours counter on the 13th count and then advance the counter one count so the display will indicate one ("1"). The 74HC00 quad NAND gate only has 4 sections with two inputs each so I used 3 diodes to detect the 13th hour (10 +1 +2 =13) which drives an inverter and also a transistor inverter (2N3904 or similar). The last 74HC14 inverter stage (pin 12 and 13) supplies a falling edge to the hours counter which advances the hours to "1" a short time after the reset pulse from the transistor inverter ends.

The pulse width from pin 12 of the inverter is a little shorter than from pin 10 which ensures that the hours clock line (pin 1 of yellow box) will move high before the end of the reset pulse form pin 10. If it were the other way around, the reset pulse may end before pin 12 of the inverter had a chance to reach a high level which would prevent the counter from advancing to "1". So it is important to use a shorter RC time at pin 13 than for the other Schmitt Trigger inputs. I used a 10K resistor and a 0.01uF cap to obtain the shorter time, but other values will work just as well. Only 2 sections of the 4071 OR gate are used, so the remaining 4 inputs (pins 8,9,12,13) should be terminated to ground if not used.

Copied Files Notice: This circuit diagram and text description has been copied and reposted without permission at: http://www.csgnetwork.com/binclockschnpl.html. The copied file has also been altered to remove the author's name and date of creation which is a clear violation of copyright law. They have also copied and modified three Java Script Calculators from this website. I have e-mailed a request to have the calculators removed and received no answer. I have also contacted the web host at Verio.net and received an autoresponse that the matter will be investigated but I doubt any action will occur. Please feel free to e-mail your opinions of plagiarism to webmaster@csgnetworks.com

Parts List:
3 - 74HC390 - Dual BCD counters
1 - CD4040 - 12 Stage Binary Counter
1 - 74HC14 - Hex Schmitt Trigger Inverter
1 - 74HC00 - Quad NAND gate
1 - CD4071 - Quad OR gate
1 - 2N3053 - NPN transistor (may need heat sink)
1 - 2N3904 - NPN transistor
3 - 1N914 - Signal diode (1N400X will also work)
2 - 1N400X - Rectifier diodes
1 - 6.2 volt - Zener diode
1 - 3300uF - Filter Capacitor - 16 volt
1 - Power Transformer - Radio Shack 273-1365A or similar
1 - 220K 1/4 or 1/8 watt resistor
1 - 150 ohm 1/4 watt resistor
19 - 220 ohm 1/4 or 1/8 watt resistors
11 - 10K 1/4 or 1/8 watt resistors
2 - 0.01uF capacitors
4 - 0.1uF capacitors
19 - Red LEDs (15 mA)
2 - Momentary push button switches (to set the time)
1 - Toggle switch (to start the clock at a precise time)

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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.  

28 LED Clock Timer Circuit Diagram

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.

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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.

72 LED Clock  Circuit Diagram

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.

50 Hertz LED Clock Timebase

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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Binary Coded Decimal (BCD) Clock

The clock circuit above uses seven ICs and 19 LEDs to indicate binary coded decimal time. The LEDs can be arranged (as shown in example above) so that each horizontal group of 3 or 4 LEDs represents a decimal digit between 0 and 9 and each individual LED represents a single bit or (binary digit) of the value. Binary digits have only two values (0 and 1) so a number written in binary would be something like 1001 or 0011, which represents decimal numbers 9 and 3 respectively. From right to left, each binary (1) represents increasing powers of 2, so that a 1 in the right hand place represents 2^0=1 and the next place to the left is 2^1=2 and then 2^2=4, and so forth.


This makes binary counting fairly easy since each digit has a value of twice the one before or 1,2,4,8,16,32,64,etc. Thus the decimal value can be found by simply adding the values of each illuminated LED in the same row, (the total is shown in the box to the right). For example, the binary number 1001 would have a decimal value of 8+0+0+1 = 9. But this is actually a binary coded decimal 9 since only values from 0 to 9 are used 0000 to 1001. A true binary clock indicating minutes of the hour would display values from 0 to 59, or 000000 to 111011. But this would be more difficult to read since adding values 32 + 16 + 8 + 2 + 1 = 59 is not as easy as 8 + 0 + 0 + 1 = 9.

Binary Coded Decimal (BCD) Clock Circuit diagram

The circuit is powered by a small 12.6 VAC transformer which also provides a low voltage 60 Hz signal for a very accurate time base. The transformer is connected with the secondary center tap at ground which produces about 8 volts DC across the 3300uF filter capacitor. DC power for the circuit is regulated at about 5.5 using a NPN transistor (2N3053) and 6.2 volt zener diode. The 2N3053 gets a little warm when several LEDs are on, and may require a little (top hat type) heat sink.

A one second clock pulse is obtained by counting 60 cycles of the AC line signal. This is accomplished using a CMOS CD4040 12 stage binary counter (shown in light blue). The 60th count is detected by the two NAND gates connected to pins 2,3,5,and 6 of the counter. When all four of these lines are high, the count will be 60 resulting in a high level at pin 4 of the 74HC14 which resets the counter to zero and advances the seconds counter (74HC390 shown in purple) when pin 4 returns to a low state.

The same process is used to detect 60 seconds and 60 minutes to reset the counters and advance the minutes and hours counters respectively. In both of these cases the 2 and 4 bit lines of the tens counter section will be high (20+40=60). In all three cases (seconds, minutes and hours) a combination 10K resistor and 0.1uF capacitor is used at the input to the 74HC14 inverter to extend the pulse width to about 300uS so the counters will reliably reset. Without the RC parts, the reset pulse may not be long enough to reset all stages of the counter since as soon as the first bit resets, the inputs to the NAND gate will no longer all be high and the reset pulse will end. Adding the RC parts eliminates that possibility.

The reset process for the hours is a little different since for a 12 hour clock we need to reset the hours counter on the 13th count and then advance the counter one count so the display will indicate one ("1"). The 74HC00 quad NAND gate only has 4 sections with two inputs each so I used 3 diodes to detect the 13th hour (10 +1 +2 =13) which drives an inverter and also a transistor inverter (2N3904 or similar). The last 74HC14 inverter stage (pin 12 and 13) supplies a falling edge to the hours counter which advances the hours to "1" a short time after the reset pulse from the transistor inverter ends.

The pulse width from pin 12 of the inverter is a little shorter than from pin 10 which ensures that the hours clock line (pin 1 of yellow box) will move high before the end of the reset pulse form pin 10. If it were the other way around, the reset pulse may end before pin 12 of the inverter had a chance to reach a high level which would prevent the counter from advancing to "1". So it is important to use a shorter RC time at pin 13 than for the other Schmitt Trigger inputs. I used a 10K resistor and a 0.01uF cap to obtain the shorter time, but other values will work just as well. Only 2 sections of the 4071 OR gate are used, so the remaining 4 inputs (pins 8,9,12,13) should be terminated to ground if not used.

Copied Files Notice: This circuit diagram and text description has been copied and reposted without permission at: http://www.csgnetwork.com/binclockschnpl.html. The copied file has also been altered to remove the author's name and date of creation which is a clear violation of copyright law. They have also copied and modified three Java Script Calculators from this website. I have e-mailed a request to have the calculators removed and received no answer. I have also contacted the web host at Verio.net and received an autoresponse that the matter will be investigated but I doubt any action will occur. Please feel free to e-mail your opinions of plagiarism to webmaster@csgnetworks.com

Parts List:
3 - 74HC390 - Dual BCD counters
1 - CD4040 - 12 Stage Binary Counter
1 - 74HC14 - Hex Schmitt Trigger Inverter
1 - 74HC00 - Quad NAND gate
1 - CD4071 - Quad OR gate
1 - 2N3053 - NPN transistor (may need heat sink)
1 - 2N3904 - NPN transistor
3 - 1N914 - Signal diode (1N400X will also work)
2 - 1N400X - Rectifier diodes
1 - 6.2 volt - Zener diode
1 - 3300uF - Filter Capacitor - 16 volt
1 - Power Transformer - Radio Shack 273-1365A or similar
1 - 220K 1/4 or 1/8 watt resistor
1 - 150 ohm 1/4 watt resistor
19 - 220 ohm 1/4 or 1/8 watt resistors
11 - 10K 1/4 or 1/8 watt resistors
2 - 0.01uF capacitors
4 - 0.1uF capacitors
19 - Red LEDs (15 mA)
2 - Momentary push button switches (to set the time)
1 - Toggle switch (to start the clock at a precise time)

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Digital Clock with Timer and Solar Panel Regulator

This is a combination digital clock timer and solar panel charge controller used to maintain a deep cycle battery from a solar panel. The timer output is used to control a 12 volt load for a 32 minute time interval each day. Start time is set using 9 dip switches and ends 32 minutes later. The 32 minute duration is set by selecting the 5th bit (2^5 = 32) of a 4040 binary counter (pin 2). The timer also has a manual toggle switch so the load can be manually switched on or off and automatically shuts off after 32 minutes. The time duration can be longer or shorter (8,16,32,64,128,256 minutes etc.) by selecting the appropriate bit of the counter. The timer circuit is shown in the lower schematic just above the regulator.  

Basic Clock Circuit diagram

The basic clock circuit (top schematic below) is similar to the binary clock (on another page) and uses 7 ICs to produce the 20 digital bits for 12 hour time, plus AM and PM. A standard watch crystal oscillator (32,768) is used as the time base and is divided down to 1/2 half second by the 4020 binary counter. One half of a 4013 data latch is used to divide the 1/2 second signal by 2 and produce a one second pulse that drives the seconds counter (74HC390 colored purple). The minutes are advanced by decoding 60 seconds (40 + 20) and then resetting the seconds counter to 0 and at the same time advancing the minutes counter. The same procedure is used to advance the hours. The second half of the 4013 latch is used to indicate AM or PM and is toggled by decoding 13 hours and resetting the hours to 0 and then advancing the hours to "one".


Clock Display Circuit diagram

The clock display circuit is shown in the second drawing below and uses 6 more ICs to decode the binary data and drive four seven segment LED displays. The 10s of hours digit is driven with a single 3904 transistor. Two multiplexer circuits (4053) are used to manually select either minutes or seconds for the right two display digits. The two switches shown between the 4053s and below the left 4053 are both part of one DPDT switch which selects either seconds or minutes for the 1X and 10X digits. This switch is shown in the seconds position and the hours digits are blanked with a low signal on pin 4 of the 4511.

The display can also be toggled on and off (totally blank) using a set/reset latch made from a couple 74HC00 NAND gates. A momentary DPDT switch is used to control the latch and toggle the display on or off. The second pole of this switch is used on the upper drawing (connected to the run/stop switch) to set the hours and minutes. Thus this same switch performs both functions of blanking the display and setting the time. The run/stop switch is shown in the normal running mode and supplies a low signal to a NAND gate which prevents accidental setting the time while the clock is running.

 Clock Timer Circuit diagram

The run/stop switch also turns on the display (through the diode D2) when in the stop position. The procedure for setting the clock would be to set the (run/stop) switch the stop position and the (seconds/minutes) switch to the minutes position. Then toggle the momentary switch to set minutes and hours of the current time plus one minute. The clock can then be started with the run/stop switch at precisely the right time (+/- 0.5 seconds).

Voltage Regulator (13.6 volts)

The voltage regulator in the lower drawing maintains the battery at 13.6 volts and also supplies the clock and timer circuits with 4.3 volts. The charge LED indicator only comes on when the regulator is supplying max charge to the battery. When the battery voltage reaches 13.6 the regulator reduces the current to whatever is necessary to maintain the voltage and the charge indicator will turn off. The unit I built also included a battery condition indicator (voltmeter using 4 LEDs) to indicate the battery condition so that a failure of the regulator would be indicated by the charge indicator LED turned off and less than 4 LEDs lit on the voltmeter.

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