Here we have an unique application for an advertisement display such as “WELCOME” “HAPPY BIRTHDAY” or a shop display. It can be used a window display of a product or simply as a name board. It can be used as warning display at “ENTRY’ or “EXIT” places or at manholes or “MEN AT WORK.” Any letter in any language can be configured into a series of light bulbs operated at mains.
It does not use microprocessors and soft wares or EPROMs but a simple TTL shift register chip known as 74 LS 164. For the display it uses conventional series set operated at mains supply but LEDs also can be used. (LED scheme is not given here) Triacs are used for direct AC switching and hence relays are dispensed with. Each letter glows one after the other, stays on until all the letters are on. All of them go off at the last clock pulse and stay off for one clock pulse.
If you do not wish to use letters as display, you may use the series sets as they also can be configured around various parts of a statue or a display item. It gives a dynamic effect as the lights come up one after the other. Speed of the display movement can be easily adjusted. Creativity is limitless!! You may use it to display your own name plate using LEDs. Wonderful it will be as the moving letters attract attention!
74LS164 is a serial in parallel out shift register. In this IC, data coming serially into the input of the IC are split, registered into 8 bits and available as parallel outputs. Hence the serial data is effectively split into parallel bits. ICs are also available with designations of Parallel In- Parallel Out, Parallel In -Serial Out. Pin out of 74164 is given in Figure 27 and triac configuration in Figure 28.
The circuit is shown in Schematic 19. IC1 555 generates the clock pulses and are fed serially, i.e., one after the other into it at Pin 8 of IC2. The frequency of these pulses is adjustable by R18 preset potentiometer. IC2 registers these pulses in parallel and releases to outputs at Q0 .
voltage arcs do not jump across. It is good idea to remove alternate tracks and mount triacs. 100K preset R18 is the speed control. BT 136 triacs can easily drive 500 W of power. Suitable heat sink must be firmly fixed for each triac individually. Mounting is similar to LM317.
Do not touch any part of the circuit while it is in operation.
Take for instance display of WELCOME. Take a hylum or plywood board of say, of 0.75 meter wide and of suitable length. Take a mains operated series set of bulbs and form the letter ‘W in the board and terminate. Then take another series set form it as letter ‘E’ and terminate. Similarly make the series sets for all other letters. You may drill and fix the bulbs in the forms of letters also. These terminals are connected to the outputs of the triacs Q9 to Q15. The other end of letter bulbs are made common and connected to the neutral side of mains.
If you wish to use LEDs instead of direct mains bulbs, you may do so. It will not be a good idea to use LEDs at mains voltage at this stage. You may use 12 or 18 power supply, thus making the whole circuit safer to handle. (Keep the 5V regulator for ICs, nevertheless.) Remove the triacs. Connect LED in series marking the polarity. Number in a series depends on the voltage you wish to use and LED voltage. For instance a red LED requires 1.7 Volts and green, orange and yellow needs about 2.0 Volts. And that is precisely the reason why you can not mix colors in the same series. However you can connect a number of series of the same color in parallel and connect them to the output transistor keeping in mind BC 147 can handle 250 milliwatts of power. Use a current limiting resistor. BEL187 is a better choice which can handle about 1 W with a small heat sink.
Qr…Q7up to 8 pulses. In this case Q0, Q1….._Q7 goes high and stay that way until reset.
These pulses drive transistors Qj to Q7, which in turn fire triacs Q9 to Q15. As these pulses are now connected to mains 230V AC, by the action of triacs, light bulbs glow one after another.
You can drive a series of lights as different letter of a message, for instance WELCOME. Q9 Triac drives a serial set configured as W, Q10 drives E and so on. After all the letters are lit up the display goes blank for one pulse time and starts all over again.
Speed of these pulses can be adjusted at IC 1 with R18. Q8 actually resets the IC at every 8th pulse so that the display starts all over again. If you want only 4 letters are to be displayed, shift the reset to 5th output. You can cascade more ICs to get more and more letters on display. But the limit of output current is 10 mA for any segment and this has to be strictly maintained.
The triac is a three terminal semiconductor for controlling current in either direction. If you notice the symbol, you will find that it looks like two SCRs in parallel (opposite direction) with one trigger or gate terminal. The power terminals are designated as Main Terminall (MT1) and Main Terminal! (MT2). It can be treated as TRIGGER AC. Unlike SCR it can trigger in both directions with a small voltage applied at the gate. Minimum holding current, must be maintained in order to keep a triac conducting. Main terminals are not interchangeable.
Entire circuit works on mains supply and you are forewarned. Now Ul IC is TTL version. Unlike CMOS ICs, static electricity does not pose a problem for TTL ICs but these cannot tolerate voltage variations. A regulated voltage of 5V is strictly required. Use 9V full wave rectifier and 7805 regulator.
In general ICs do not like bad housekeeping, more so when handling mains voltages. Soldering is straightforward. A piece of Vero board is OK. But if you are mounting triacs on the same board it is very important to have enough space between tracks such that high
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