AFX Slot Car Lap Counter

AFX slot car sets are very enjoyable but you can increase the fun with a lap counter. This circuit will count from 00 to 99, with independent counters for each track. The sensing device used is a Hall effect sensor (UGN3503; available from Dick Smith Electronics). One of these sensors is glued under a section of each track (printed side up); between the slot and one of the track rails is the best spot. In this position, it will allow the ground effects magnets on the cars to pass over them. The sensor will provide a voltage of about 3V when a car passes over it and about 2V without a magnetic field. Both counter circuits are identical, with dual op amp IC5 handling the signals from both sensors.

 

IC5a and IC5b are wired as comparators, with a 2.5V reference derived from zener diode ZD1 via the 10kO and 12kO resistors. Each time the output of IC5a goes high it clocks IC1a, a 4518 BCD counter. NAND gates IC2a & IC2b provide a carry out to the other half of IC1 for a 2-digit display. More counters may be cascaded this way to provide extra digits. The BCD outputs of IC1 drive 7-segment decoders IC3 & IC4 which drive common cathode LED displays. Push-button S1 resets the counters to 00 for both tracks for the start of a new race.

Heart Rate Monitor

Strictly speaking, this simple circuit shouldn't work! How could anyone expect an ordinary light dependent resistor photo cell to 'see' through a fingertip in natural daylight and detect the change in blood flow as the heart pulsates? The secret is a high gain circuit, based on a dual op amp IC which can be either the low power LM358 or the JFET TL072. The LDR is connected in series across the 9V battery supply via a 100kO resistor (R1) and the minute signal caused by the blood pulsing under the skin is fed to the non-inverting (+) input, pin 3, of IC1a via a 0.µF capacitor.

Pin 3 is biased by a high impedance voltage divider consisting of two 3.3MO resistors. The feedback resistors to pin 2 set the gain to 11 times. The output of IC1a is fed via a 0.47µF capacitor and 220kO resistor to IC1b. This is configured as an inverting op amp with a gain of 45 so that the total circuit gain is about 500. The output of IC1b is used to drive an analog meter which may be a multimeter set to the 10V DC range or any panel meter in series with a resistor to limit the current to less than its full-scale deflection. The prototype used an old VU meter with a 47kO resistor fitted in series.

 

 

Note that the unit was designed to use the Dick Smith Electronics light dependent resistor (Z-4801). Other LDRs may require a change in the value of resistor R1. A light source such as a high brightness LED is not required. All that is needed is a reasonably well-lit room, preferably natural daylight, to produce a healthy swing of the needle. Only when the hands are very cold does it make it a little more difficult to accurately count the pulses. To check your heart rate, carefully position your thumb or finger over the LDR and count the meter fluctuations for a period of 15 seconds. Then multiply the result by four to obtain your pulse rate. The circuit can not be used if you are walking or running, etc.

Digital Step-Km Counter Circuit Schematic

This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking.

A beeper (excludable), signals each count unit, occurring every two steps. A normal step was calculated to span around 78 centimeters, thus the LED signaling 50 meters illuminates after 64 steps (or 32 operations of the mercury switch), the display indicates 100 meters after 128 steps and so on.

For low battery consumption the display illuminates only on request, pushing on P2. Accidental reset of the counters is avoided because to reset the circuit both pushbuttons must be operated together. Obviously, this is not a precision meter, but its approximation degree was found good for this kind of device. In any case, the most critical thing to do is the correct placement of the mercury switch inside of the box and the setting of its sloping degree.

Parts:

R1 = 22K 1/4W Resistor
R2 = 2.2M 1/4W Resistor
R3 = 22K 1/4W Resistor
R4 = 1M 1/4W Resistor
R5 = 4.7K 1/4W Resistor
R6 = 47R 1/4W Resistor
R7 = 4.7K 1/4W Resistor
R8 = 4.7K 1/4W Resistor
R9 = 1K 1/4W Resistor

C1 = 47nF 63V Polyester Capacitor
C2 = 100nF 63V Polyester Capacitor
C3 = 10nF 63V Polyester Capacitor
C4 = 10µF 25V Electrolytic Capacitor

D1 = Common-cathode 7-segment LED mini-display (Hundreds meters)
D2 = Common-cathode 7-segment LED mini-display (Kilometers)

Q1 = BC327 45V 800mA PNP Transistors
Q2 = BC327 45V 800mA PNP Transistors

P1 = SPST Pushbutton (Reset)
P2 = SPST Pushbutton (Display)

IC1 = 4093 Quad 2 input Schmitt NAND Gate IC
IC2 = 4024 7 stage ripple counter IC
IC3 = 4026 Decade counter with decoded 7-segment display outputs IC
IC4 = 4026 Decade counter with decoded 7-segment display outputs IC

SW1 = SPST Mercury Switch, called also Tilt Switch
SW2 = SPST Slider Switch (Sound on-off)
SW3 = SPST Slider Switch (Power on-off)

BZ = Piezo sounder
B1 = 3V Battery (2 AA 1.5V Cells in series)

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Circuit operation:

IC 1A & IC 1B form a monostable multi vibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divides by 64. Q2 drives the LED dot-segment of D1 every 32 pulses counted by IC2. Either IC3 & IC4 divide by 10 and drive the displays. P1 resets the counters and P2 enables the displays. IC1C generates an audio frequency square wave that is enabled for a short time at each monostable count. Q1 drives the piezo sounder and SW2 allows disabling the beep.

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Notes:

• Experiment with placement and sloping degree of mercury switch inside the box: this is very critical.
• Try to obtain a pulse every two walking steps. Listening to the beeper is extremely useful during setup.
• Trim R6 value to change beeper sound power.
• Push P1 and P2 to reset.
• This circuit is primarily intended for walking purposes. For jogging, further great care must be used with mercury switch placement to avoid undesired counts.
• When the display is disabled current consumption is negligible, therefore SW3 can be omitted.

Automatic Water Tank Filler Circuit Diagram

This circuit has been very useful in filling a header tank for a reticulated water supply on a farm. Eight troughs are supplied in different paddocks where a lack of water would have serious consequences for the stock. In the past, the tank had been filled daily by a time clock which was not successful. During hot weather, the stock would empty the tank on a regular basis and then be without water for several hours or the tank would overflow and flood the area if the weather was wet and the cattle did not drink much.

The circuit described has been used to maintain the level of water in the header tank within prescribed limits. It controls a 3HP submersible bore pump which has a high starting current, necessitating a solid-state relay sufficient to take the starting load. Two Darlington transistors, Q1 & Q3, in conjunction with Q2 & Q4, are connected to the upper and lower water sensors in the tank. Q2 & Q4 have a common 5.6kO load resistor and function as a NOR gate. The output of the NOR gate drives Q5 which activates relay RLY1.

Initially, when the water level is low, both sensors will be open-circuit, the NOR gate output will be high and the relay will be turned on. This causes the normally closed (NC) contacts of the relay to open and disconnect the lower sensor. However, the upper sensor will still be open circuit and the NOR gate output will be high, keeping the relay closed. The normally open (NO) contact of the relay will be closed to operate the solid-state relay RLY2 to run the pump.

This state continues until the water reaches the top sensor which will then drop the output from the NOR gate to 0V. The disables relay RLY1 and the pump is stopped. In practice the upper level sensor is just below the overflow from the tank and the lower sensor about half way up the tank. The sensor contacts are simply two stainless steel screws about 25mm apart and screwed through the poly tank walls. The wiring junctions on the side of the tank are protected by neutral-cure silicone sealant.

Remote Operated Home Appliances Circuit

Here is the circuit diagram of Remote Operated Home Appliances or Remote controlled Home appliances. Connect this circuit to any of your home appliances (lamp, fan, radio, etc) to make the appliance turn on/off from a TV, VCD, VCR, Air Conditioner or DVD remote control. The circuit can be activated from up to 10 meters. It is very easy to build and can be assembled on a veroboard or a general-purpose PCB.

Parts:

R1 = 220K
R2 = 330R
R3 = 1K
R4 = 330R
R5 = 47R
C1 = 100uF-16V
C2 = 100nF-63V
C3 = 470uF-16V
D1 = 1N4007
D2 = Red LED
D3 = Green LED
Q1 = BC558
Q2 = BC548
IR = TSOP1738
IC1 = CD4017
RL1 = Relay 5V DC

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Circuit Operation:

The 38kHz infrared rays generated by the remote control are received by IR receiver module TSOP1738 of the circuit. Pin 1 of TSOP1738 is connected to ground, pin 2 is connected to the power supply through R5 and the output is taken from pin 3. The output signal is amplified by Q1. The amplified signal is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to vcc and pin 3 is connected to D2 (Red LED), which glows to indicate that the appliance is ‘off.’

The output of IC1 is taken from its pin 2. D3 connected to pin 2 is used to indicate the ‘on’ state of the appliance. Q2 connected to pin 2 of IC1 drives relay RL1. D1 acts as a freewheeling diode. The appliance to be controlled is connected between the pole of the relay and neutral terminal of mains. It gets connected to live terminal of AC mains via normally opened (N/O) contact when the relay energizes. If you want to operate a DC 12 volt relay then use a regulated DC 12 volt power supply for DC 12 volt Relay and remember that the circuit voltage not be exceeded more than DC 5 volts

Direction Sensitive Light Barrier

With two light barriers closely positioned one after the other it is possible to establish in which direction they have been crossed. If, for example, you place it at the entrance of the toilet then you can use it to control the lights: on when entering and off when leaving the room. The circuit for this has many similarities with the modulated light barrier appearing else-where in this Summer Circuits issue. There are two ways to position the light barriers, namely a completely duplicated installation in opposing directions (this to prevent mutual interference) and a version with one IR transmitter and two receivers.

Direction Sensitive Light Barrier Block Diagram

Both types of installation are shown here, which one is most suitable depends on the actual application. When used in a doorway, one transmitter is sufficient if the receivers are placed about 5 cm apart. With a wider passage, an installation with two separate IR-transmitters is a better solution. This circuit has a range of several meters, even if the sun shines directly on the receiver! We use the exact same IR-transmitter(s) as for the modulated light barrier. For the installation with two separate IR-transmitters it is sufficient to duplicate R6, T1, D1, C3 and R7 from the circuit of the modulated light barrier.

 

 

Direction Sensitive Light Barrier Circuit Diagram

Output OUT (pin 3) of IC2 can drive two of these IR-drivers without any difficulty. The receivers are slightly different than those of the modulated light barrier and the circuit is the same for both types of installation. We again use the TSOP1736, which is sensitive to IR-light that is modulated at a frequency of 36 kHz. D2, R8 and C4 ensure that the received pulses from IC3 at the output of IC5a result in a ‘1’ when the beam is not interrupted. When the beam is interrupted this output will become a ‘0’ within about 1 ms.

In the same way IC5b generates a ‘0’ when IC4 stops receiving IR-light. The 4013 CMOS-IC used here contains two D-flipflops, of which we use only one. The instant that light barrier 2 (IC4) is unblocked again, is used to clock the state of light barrier 1 (IC3) through to output Q1. This signal drives the relay via T2, which operates the light in the room. The circuit therefore turns the light on or off the moment that light barrier 1 is uninterrupted.

Light Gate With Counter Using 555 And 4033

The circuit described here counts the number of times that an infrared beam is interrupted. It could be used to count the number of people entering a room, for instance, or how often a ball or another object passes through an opening (handy for playing shuffleboard). The heart of the circuit consists of - you guessed it - a light gate! Diode D1 is an IR diode that normally illuminates IR transistor T1. The light falling on T1 causes it to conduct to a certain extent. The resulting voltage on the collector of T1 should be just low enough to prevent the following transistor (T2) from conducting. This voltage can be adjusted within certain limits using P1.

As soon as an object comes between D1 and T1, the light shining on T1 will be partially or fully blocked, causing the IR transistor to conduct less current. As a result, the voltage on its collector will increase, producing a brief rise in the voltage on the base of T2. This will cause T2 to conduct and generate a negative edge at IC1. This negative edge will trigger the monostable multivibrator, which will then hold the output signal on pin 3 ‘high’ for a certain length of time (in this case, one second). At this point, two things will occur. First, a buzzer will be energized by the output of IC1 and produce a tone for approximately one second.

When the buzzer stops, a negative edge will be applied to the clock input of IC2, causing the counter in IC2 to be incremented by 1. IC2 is conveniently equipped with an internal binary-to-BCD decoder, so its outputs only have to be buffered by IC3 and T3 to allow the state of the counter to be shown on the 7-segment display. Switch S1 can be used to reset the counter to zero. If a one-second interval does not suit your wishes, you can modify the values of R3 or C1 to adjust the time. Increasing the value of R3 lengthens the interval, and decreasing it naturally shortens the interval.

The same is true of C1. When building the circuit, make sure that T1 is well illuminated by the light from D1, while at the same time ensuring that T1 ‘sees’ as little ambient light as possible. This can best be done by fitting T1 in a small tube that is precisely aimed toward D1. The longer the tube, the less ambient light will reach T1. The sensitivity of the circuit can be adjusted using P1.

Fully Adjustable Power Supply

Based on a National Semiconductor application note, this circuit uses an LM317 3-terminal regulator (REG1), chosen because of its built-in over-current and over-temperature protection. Its output is boosted up to just over 5A by the MJ2955 transistor (Q1). The output voltage is varied by adjusting the voltage on REG1’s ADJ terminal using VR1 (a 10kO potentiometer), via the 270O resistor. Adjustable current limiting is provided by op amp IC1, used as a comparator, which monitors the voltage across the 0.1O current sensing resistors. Once this voltage exceeds a level set by potentiometer VR2, then its output goes low, dragging down the adjust pin of REG1 and thus the output voltage.

LED1 illuminates when current limiting is occurring. The 10kO voltage adjust potentiometer (VR1) has one side connected to -5V instead of 0V so that the output voltage can be varied down to 0V instead of 1.2V (normal limit of an LM317). Trimpot VR3 is adjusted to set the minimum output voltage to +100mV or so. Note that because the -5V rail is used as a reference, it should be regulated using an LM7905 or similar. The LM317 3-terminal regulator and Q1 should be mounted on the same heatsink to take advantage of REG1’s thermal control.

Water reservoir automatic level control, Simple circuitry - 12V supply

By means of a Relay, employed to drive a water pump, this circuit provides automatic level control of a water reservoir or well. The shorter steel rod is the "water high" sensor, whereas the longer is the "water low" sensor. When the water level is below both sensors, IC1C output (pin #10) is low; if the water becomes in contact with the longer sensor the output remains low until the shorter sensor is reached. At this point IC1C output goes high, Q1 conducts, the Relay is energized and the pump starts operating.

Now, the water level begins to decrease and the shorter sensor will be no longer in contact with the water, but IC1C output will be hold high by the signal return to pin #5 of IC1B, so the pump will continue its operation. But when the water level falls below the longer sensor, IC1C output goes low and the pump will stop. SW1 is optional and was added to provide reverse operation. Switching SW1 in order to connect R3 to pin #11 of IC1D, the pump will operate when the reservoir is nearly empty and will stop when the reservoir is full. In this case, the pump will be used to fill the reservoir and not to empty it as in the default operating mode.

 Parts:

R1 = 15K - 1/4W Resistors
R2 = 15K - 1/4W Resistors
R3 = 10K - 1/4W Resistor
R4 = 1K - 1/4W Resistor
D1 = LED - any type and color
D2 = 1N4148 - 75V 150mA Diode
Q1 = BC337 - 45V 800mA NPN Transistor
IC1 = 4001 Quad 2 Input NOR Gate CMos IC
SW = SPDT Toggle or Slide Switch (Optional)
RL1 = Relay with SPDT 2A @ 230V switch
Coil Voltage 12V - Coil resistance 200-300 Ohm
Two steel rods of appropriate length

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Notes:

• The two steel rods must be supported by a small insulated (wooden or plastic) board.
• The circuit can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the circuit's negative ground.

Simple Digital Switching System

This circuit can control any one out of 16 devices with the help of two push-to-on switches. An up/down counter acts as a master-controller for the system. A visual indication in the form of LEDs is also available.  IC1 (74LS193) is a presettable up/ down counter. IC2 and IC3 (74LS154) (1of 16 decoder/demultiplexer) perform different functions, i.e. IC2 is used to indicate the channel number while IC3 switches on the selected channel.

Digital Switching System Circuit Diagram :

 

Before using the circuit, press switch S1 to reset the circuit. Now the circuit is ready to receive the input clock. By pressing pressing switch S2 once, the counter advances by one count. Thus, each pressing of switch S2 enables the counter to advance by one count. Likewise, by pressing switch S3 the counter counts downwards.

The counter provides BCD output. This BCD output is used as address input for IC2 and IC3 to switch one (desired channel) out of sixteen channels by turning on the appropriate triac and the corresponding LED to indicate the selected channel.  The outputs of IC3 are passed through inverter gates (IC4 through IC6) because IC3 provides negative going pulses while for driving the triacs we need positive-going pulses. The high output of inverter gates turn on the npn transistors to drive the triacs. Diodes connected in series with triac gates serve to provide unidirectional current for the gate-drive.

Simple Electronic Code Lock

The circuit diagram of a simple electronic code lock is shown in figure. A 9-digit code number is used to operate the code lock.When power supply to the circuit is turned on, a positive pulse is applied to the RESET pin (pin 15) through capacitor C1. Thus, the first output terminal Q1 (pin 3) of the decade counter IC (CD 4017) will be high and all other outputs (Q2 to Q10) will be low. To shift the high state from Q1 to Q2, a positive pulse must be applied at the clock input terminal (pin 14) of IC1. This is possible only by pressing the push-to-on switch S1 momentarily.

Circuit diagram:

 

 

 

On pressing switch S1, the high state shifts from Q1 to Q2. Now, to change the high state from Q2 to Q3, apply another positive pulse at pin 14, which is possible only by pressing switch S2. Similarly, the high state can be shifted up to the tenth output (Q10) by pressing the switches S1 through S9 sequentially in that order. When Q10 (pin 11) is high, transistor T1 conducts and energises relay RL1. The relay can be used to switch ‘on’ power to any electrical appliance. Diodes D1 through D9 are provided to prevent damage/malfunctioning of the IC when two switches corresponding to ‘high’ and ‘low’ output terminals are pressed simultaneously.

Capacitor C2 and resistor R3 are provided to prevent noise during switching action. witch S10 is used to reset the circuit manually. Switches S1 to S10 can be mounted on a keyboard panel, and any number or letter can be used to mark them. Switch S10 is also placed together with other switches so that any stranger trying to operate the lock frequently presses the switch S10, thereby resetting the circuit many times. Thus, he is never able to turn the relay ‘on’. If necessary, two or three switches can be connected in parallel with S10 and placed on the key-board panel for more safety. A 12V power supply is used for the circuit. The circuit is very simple and can be easily assembled on a general-purpose PCB. The code number can be easily changed by changing the connections to switches (S1 to S9).

Electronic Code Lock

Nowadays, electronic code locks are usually based on microcontrollers. However, if you like your electronics discrete, you will enjoy the battery-operated circuit shown here. Since the circuit automatically switches off after the door has been opened and draws no current in the idle state, three alkaline batteries (mignon, AA or R6 cells) are good for around 5,000 door openings. The main advantage is that the door opener can also be powered from the battery, so it’s not necessary to run any extra cables.

 

Project  Image :

 

 

Figure 1 shows the schematic diagram of the circuit, which is split into two parts. The first part is the control panel, which consists of a 12-position keypad and two LEDs. The second part is the programming and evaluation logic, which contains only standard logic ICs. The control panel is connected to the logic board by a 16-way flat cable. The keypad circuit is laid out with separate connections to the individual switches, instead of a matrix. The code is programmed using the two pin connector strips K1 and K2.  The circuit allows any desired combination of numbers to be used for the code, up to a maximum of 9 positions. Press-ing a particular button, which in principle is random but which naturally must be specified in advance, awakens the circuit from the zero-current idle state. This Start button cannot be used in the subsequent code sequence. The Start button is programmed by connecting a wire bridge from the associated pin of K2 to pin 1 of K1.  The code sequence is programmed in a similar manner. The first numeral of the code is programmed by connect-ing the associated pin of K2 to pin 2 of K1, the connection for the second numeral is made to pin 3 of K1, the third to pin 4 and so on. Numerals that are not used in the code do not actually have to be connected. However, if the unused buttons are connected to VDD, the code lock will assume that an error has occurred if any of these buttons is pressed and will reset the circuit. Pressing the Start button switches on transistor T1, which connects the supply voltage source to the code lock. This is indicated by the yellow LED (D20).

 

Circuit diagram :

 

 

Part List :

Resistors :

R1,R2 = not fitted
R3 = 220kΩ
R4,R5 = 1MΩ
R6 = 220kΩ
R7,R9,R10,R17 = 100kΩ
R8,R12,R14 = 2MΩ2
R11 = 560Ω
R13,R15,R20 = 1kΩ5
R16 = 100kΩ
R18 = 120Ω
R19 = 10k
R21-R24 = 3Ω3
R25-R35 = 22kΩ
Capacitors :
C1,C6,C7,C8,C10 = 100nF
C2,C3,C5 = 10nF
C4 = 1µF
C9 = 330nF
C11 = 47µF 16V radial
Semiconductors :
D1-D9,D11,D13,D14,D15,D17,
D18 = 1N4148
D10,D12 = zener diode 1V2
0.4W*
D16 = 1N4001
D19 = LED, green
D20 = LED, yellow
T1 = BC327
T2,T3,T4 = BC337
T5 = BD140
IC1 = 4017
IC2,IC3 = 4069 or 40106
Miscellaneous :
JP1 = jumper
K1,K2 = 12-way pinheader or
wire links
K3,K4 = not required (ribbon
cable )
K5, K6 = 2-way PCB terminal
block, lead pitch 5mm
S1-S12 = pushbutton with
make contact
 

Since the logic ICs are now enabled, the output of IC3f will be High, so T2 also conducts and pulls the base of T1 to ground. This means that the Start button can be released without affecting the circuit. However, C11 can now slowly charge via the high resistance of R12 until the voltage at the inverter input is high enough to cause its output to go Low, which interrupts the supply voltage to the circuit and puts it back into the idle state. The valid code must therefore be entered during the time interval determined by this R–C time constant. Once the supply voltage is disconnected, C11 discharges rapidly via D18. This is important, since other-wise C11 could retain its charge for a long time. This would make the time allowed for entering the code significantly shorter the next time the lock is used.  Pressing the Start button also has other consequences. Via the Start switch, ground potential arrives at IC2d, where it causes a pulse to be generated that places counter IC1 in a defined state (Q0 = 1) prior to the entry of the first code numeral. The first code numeral can now be entered. If the correct button is pressed, the High potential from Q0 passes through the closed switch to reach IC2d–IC2a. This net-work generates a positive pulse at the instant that the but-ton is released. This pulse clocks the counter, so that the High level from Q0 moves by one position to Q1. This process repeats itself until all code numerals have been entered. 

 

  PCB Layout :

 

 

After the ninth numeral has been entered, the positive volt-age jumps to Q9, where it charges C4 (if jumper JP1 is installed). While C4 is charging, the output of IC2e goes Low for approximately two seconds, and the output of IC3d goes high for the same interval. Power transistor T5 is switched on via R19 and T4 to supply current to the door opener. At the same time, IC3a switches on the green LED (D19) to indicate that the door can be opened. T3 limits the current through the door opener to around 700 mA. Once C4 is sufficiently charged, the output of IC2e changes to High. Not only does this switch off the door opener, but the positive edge also generates a pulse in the network IC2f/IC3c that passes through D14 to reach IC1 as a reset pulse (D14, D17 D13 and R7 together form a ‘wired-or’ gate). Inverter IC3b also provides the power-up reset to the counter. The reset signal places the circuit back into its initial state. What happens if an incorrect button is pushed? In such a case a Low level is passed through in place of the High level from the counter output. This has the same consequence as the Low level from the Start button: the counter is reset.

 

Note that you can also modify the circuit to use fewer than nine numerals for the code. All that is necessary is to connect C4 via a jumper to another counter output in place of Q9 (for example, to Q4 for a four-position code). The diode at the selected output of the counter can be replaced by a wire jumper, and the ‘higher level’ diodes can also be omit-ted. The active ‘on’ time of the door opener is 2 s. If this seems to be too short, the value of R8 or C4 can be increased. However, this also increases the amount of power drawn from the battery, especially considering that the door opener is by far the biggest power glutton in the circuit. In order to integrate the circuit into an existing door opener or to use it to operate an ac door opener, you should connect a relay to K5. Before assembling the circuit using the printed circuit board shown in Figure 2, you should separate the two sections by sawing between K3 and K4. The logic board should not be fitted directly behind the pushbuttons for entering the code. Instead, it is better to separate the entry pushbuttons, the LEDs and the door opener from the logic circuit board with a length of cable. Otherwise, a screw driver or a bit of wire connected between the emitter and collector of T5 is all that is needed to outfox the code lock and open the door.

 

Fitting the components to the circuit board should not be difficult. The ICs can be mounted in sockets. The author used 4049 inverter ICs, but in the Elektor Electronics lab prototype we used 4069’s, which are functionally compatible but not pin-compatible, and we also tried a 40106, which has Schmitt-trigger inputs. With a 4069, normal 1N4148 diodes can be used for D10 and D12. The best solution is to use the relatively noise-immune 40106. However, it is then necessary to use Zener diodes for D10 and D12, due to the higher threshold voltage. A 3.3-V type is ideal with an operating voltage of 15 V. There is one thing you should not overlook: with low-voltage zener diodes, the band on the package marks the anode instead of the cathode, as you would normally expect. At least, this is true in most cases, but not always.

 

Soldering Iron Inverter

Here is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 and Q2 (each BC547) form an astable multivibrator that produces 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to pnp Darlington driver stages formed by transistor pairs Q3-Q5 and Q4-Q6 (utilising BC558 and BD140). The outputs from the drivers are fed to transistors Q7 and Q8 (each 2N3055) connected for push-pull operation.  Use suitable heat-sinks for transistors Q5 through Q8. A 230V AC primary to 12V-0-12V, 4.5A secondary transformer (T1) is used.

 Soldering Iron Inverter Circuit diagram:

The centre-tapped terminal of the secondary of the transformer is connected to the battery (12V, 7Ah), while the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8, respectively. When you power the circuit using switch S1, transformer X1 produces 230V AC at its primary terminal. This voltage can be used to heat your soldering iron. Assemble the circuit on a generalpurpose PCB and house in a suitable cabinet. Connect the battery and transformer with suitable current-carrying wires. On the front panel of the box, fit power switch S1 and a 3-pin socket for connecting the soldering iron. Note that the ratings of the battery, transistors T7 and T8, and transformer may vary as these all depend on the load (soldering iron).

Capacitor Discharge Ignition Circuit (CDI)

The CDI ignition circuit produces a spark from an ignition coil by discharging a capacitor across the primary of the coil. A 2uF capacitor is charged to about 340 volts and the discharge is controlled by an SCR. A Schmitt trigger oscillator (74C14) and MOSFET (IRF510) are used to drive the low voltage side of a small (120/12 volt) power transformer and a voltage doubler arrangement is used on the high voltage side to increase the capacitor voltage to about 340 volts. A similar Schmitt trigger oscillator is used to trigger the SCR about 4 times per second. The power supply is gated off during the discharge time so that the SCR will stop conducting and return to it's blocking state. The diode connected from the 3904 to pin 9 of the 74C14 causes the power supply oscillator to stop during discharge time. The circuit draws only about 200 milliamps from a 12 volt source and delivers almost twice the normal energy of a conventional ignition circuit. High voltage from the coil is about 10KV using a 3/8 inch spark gap at normal air temperature and pressure. Spark rate can be increased to possibly 10 Hertz without losing much spark intensity, but is limited by the low frequency power transformer and duty cycle of the oscillator. For faster spark rates, a higher frequency and lower impedance supply would be required. Note that the ignition coil is not grounded and presents a shock hazard on all of it's terminals. Use CAUTION when operating the circuit. An alternate method of connecting the coil is to ground the (-) terminal and relocate the capacitor between the cathode of the rectifier diode and the positive coil terminal. The SCR is then placed between ground and the +340 volt side of the capacitor. This reduces the shock hazard and is the usual configuration in automotive

Generating Long Time Delays

Generating long delays of several hours can be accomplished by using a low frequency oscillator and a binary counter as shown below. A single Schmitt Trigger inverter stage (1/6 of 74HC14) is used as a squarewave oscillator to produce a low frequency of about 0.5 Hertz. The 10K resistor in series with the input (pin 1) reduces the capacitor discharge current through the inverter input internal protection diodes if the circuit is suddenly disconnected from the supply. This resistor may not be needed but is a good idea to use. The frequency is divided by two at each successive stage of the 12 stage binary counter (CD4040) which yields about 1 hour of time before the final stage (Q12) switches to a high state. Longer or shorter times can be obtained by adjusting the oscillator frequency or using different RC values. Each successive stage changes state when the preceding stage switches to a low state (0 volts), thus the frequency at each stage is one half the frequency of the stage before. Waveform diagrams are shown for the last 3 stages. To begin the delay cycle, the counter can be reset to zero by momentarily connecting the reset line (pin 11) to the positive supply. Timing accuracy will not be as good as with a crystal oscillator and may only be around 1 or 2% depending on the stability of the oscillator capacitor.

555 Tone Generator (8 ohm speaker)

This is a basic 555 squarewave oscillator used to produce a 1 Khz tone from an 8 ohm speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near squarewave.

Lower frequencies can be obtained by increasing the 6.2K value, higher frequencies will probably require a smaller capacitor as R1 cannot be reduced much below 1K. Lower volume levels can be obtained by adding a small resistor in series with the speaker (10-100 ohms). In the circuit on the right, the speaker is directly driven from the 555 timer output. The series capacitor (100 uF) increases the output by supplying an AC current to the speaker and driving it in both directions rather than just a pulsating DC current which would be the case without the capacitor. The 51 ohm resistor limits the current to less than 200 mA to prevent overloading the timer output at 9 volts. At 4.5 volts, a smaller resistor can be used.

Game Show Indicator Lights (Who's First)

Parts List:

Quantity       Description                   Radio Shack Part Number

1         4 Amp/400 Volt Bridge Rectifier            276-1173
3         Silicon Controlled Rectifier (SCR)         NTE5457
3         120 VAC/ 25 Watt incandescent lamp
1         50-100 microfarad/ 200 volt capacitor
1         1000 microfarad / 35 volt capacitor        272-1032
1         50 ohm resistor/ 5 or 10 Watt              271-133
3         Push Button Switch (normally open)
1         Push Button Switch (normally closed)
3         2K resistor, 1/4 watt                      271-1325
4         1N914 Diode
1         51K resistor, 1 watt
1         2 Amp Fuse                                 270-1064
1         Relay (SPDT) 9 Volt DC, 500 ohm coil       275-005

Ignition Coil Buzz Box

Here's a circuit to create a buzzcoil using a standard automotive ignition coil. A 556 dual timer is used to establish the frequency and duty cycle of the coil current. One of the timers is used as an oscillator to generate the 200 Hz rectangular waveform needed to control the (IRF740 MOSFET) while the second timer switches the oscillator on and off as the breaker points open and close (closed = on). The result is a steady stream of sparks from the ignition coil spaced about 5 milliseconds apart while the breaker points are closed. 

Operation:
Pin 8 and 12 are the threshold and trigger inputs of one timer which are driven by the breaker points and produce an inverted signal at the timer output (pin 9). When the points are closed to ground, pin 9 will be high and visa versa. The signal at pin 9 controls the reset line (pin 4) of the second timer and holds the output at pin 5 low while pin 4 is low and pins 8 and 12 are high (points open). The 15K and 4.7K resistors and 0.33uF capacitor are the timing components that establish the frequecy and duty cycle of the second timer which is about 4 milliseconds for the positive interval and 2 milliseconds for the negative. During the positive time interval, the MOSFET gates are held high which causes the ignition coil current to rise to about 4 amps. This equates to about 80 millijoules of energy in the coil which is released into the spark plug when the timer output (pin 5) moves to ground, turning off the MOSFET. A 12 volt zener diode is placed at the junction of the 10 and 27 ohm resistors to insure the MOSFET gate input never goes above 12 volts or lower than -0.7 volts. A 200 volt/5 watt zener is used at the MOSFET drain to limit the voltage to +200 and lengthen the spark duration. The circuit should operate reliably with a shorted plug, however operating the circuit with no load connected (plug wires fallen off, etc.) may cause a failure due to most of the power being absorbed by the zener. You can also use a transient voltage suppressor (TVS) such as the 1.5KE200A or 1.5KE300A in place of the zener. It's probably a better part, but hard to obtain.

9 Second Digital Readout Countdown Timer

This circuit provides a visual 9 second delay using a 7 segment digital readout LED. When the switch is closed, the CD4010 up/down counter is preset to 9 and the 555 timer is disabled with the output held high. When the switch is opened, the timer produces an approximate 1 second clock signal, decrementing the counter until the 0 count is reached. When the zero count is reached, the 'carry out' signal at pin 7 of the counter moves low, energizing the 12 volt relay and stopping the clock with a low signal on the reset line (pin 4). The relay will remain energized until the switch is again closed, resetting the counter to 9. The 1 second clock signal from the 555 timer can be adjusted slightly longer or shorter by increasing or decreasing the resistor value at pin 3 of the timer. 

The CD4510 is a CMOS Presettable BCD Up/Down counter which can be preset to any number between 0 and 9 with a high level on the PRESET ENABLE line, (pin 1) or reset to 0 with a high level on the RESET line (pin 9). Inputs for presetting the counter (P1, P2, P3, P4) are on pins (4, 12, 13, 3) respectively. The counter advances up or down on each positive-going clock transition (pin 15) and the counting direction (up or down) is controlled by the logic level on the UP/DOWN input (pin 10, high=up, low=down). The CARRY-IN signal (pin 5) disables the counter with a high logic level. 

The CD4511 is a CMOS BCD to 7 segment latch decoder capable of sourcing up to 25 mA which allows it to drive LEDs and other displays directly. A LATCH-ENABLE line (pin 5, active low) stores data from the BCD input lines. A LAMP-TEST input (pin 3, active low) can be used to illuminate all 7 segments, and a BLANKING input (pin 4, active low) can be used to turn all segments off. The LED display must be a common cathode type so that the segments are illuminated with a positive voltage on their respective connections. Complete data sheets for the CD4510 and CD4511 can be obtained by answer fax from

Digital Thermometer