8 Function Christmas Light Circuit

A simple mains operated, transformerless 8 function Christmas light circuit can be made by using a single IC, a rotary switch and a few SCRs, let's learn the procedures in detail.

The circuit is based on a single chip UTC8156 which is internally preprogrammed to produce 8 unique selectable light effects across 4 numbers of connected AC/DC lamps.

Usually such multi-function light effect generators are based on microcontrollers and require some complex programming but this this is a ready made preprogrammed IC which can deliver interesting changing light patterns over 4 mains operated lamps.

Circuit Application Hints

The proposed 8 function Christmas light circuit as the name suggest can be used for decoration during festivals, for example in Christmas the circuit can be applied for decorating a Christmas tree, in other popular festivals such as in Diwali the same circuit can be used for decorating door entrances, balconies and so on.

The 8 light patterns specified in the IC are very unique and can be selected using a small rotary switch with a plastic knob, this is important because the entire circuit is directly linked with the mains and therefore not isolated from the mains current, due to this reason a plastic knob for the rotary switch becomes extremely important to avoid lethal electric shocks.

The following images show the basic functional and wiring details of the proposed 8 function Christmas light circuit.

Both the designs are basically the same, the first is based on the 18 pin IC, while the second one is configured using the 16 pin IC version.

How the IC Works

The pinouts of the IC on the left are designated with the "function" specs, which can be appropriately switched using a rotary selector switch whose pole can be seen connected with the ground or the negative line of the circuit for executing the selected function.

The circuit can be operated from any desired supply input source, as per individual preference, it can be operated from the mains 220V or from mains 110V input supply using the configuration depicted above, and also from any 5 to 24V AC/DC adapter unit.

The lamps must be rated as per the input supply used, meaning for 220V it should be 220V rated lamps, for 110V the lamps ought to be 110V rated, and for 24V it should be rated at 24V

For 220V and 110V operations the involved resistors and the capacitor might need to be changed appropriately as shown in the following table:

As per the specifications, the IC is able to operate even from supplies as low as 5V, which implies that the circuit can be possibly operated through a mobile charger.

About the SCRs

As can be seen in the diagram that the supply Vdd to the IC is substantially dropped through R1, which probably means that the current to the IC and for the SCRs could be very low, in the order of a few milliamps.

Therefore here the applicable SCRs could be the smaller ones which can work with 1 to 5mA gate current such as BT169, and hence the lamps would also need to be smaller in current, for example the 10 watt or smaller lamps.

However, according to me the circuit can be appropriately modified for handling high watt mains bulbs simply by reducing R1 to 100 ohms and operating the circuit using a 5V cellphone charger and replacing the SCRs with C106 type of SCRs.

But with the above case the bulb top rail will need to be connected to one of the mains input for example the phase, and the negative common rail of the circuit will be required to be connected with the neutral line.

8 Functions Light effect

The IC is specified to generate the following 8 different light effect patterns as per the position of the rotary switch within the stipulated selection pinouts

1) The IC continuously scans and randomly generates the 8 functions in a row.

2) In this position the IC generates a wave like effect on the connected lamps.

3) In this mode the lights are illuminated in sequence one after the other and shutting off in the same order.

4) The fourth selection gives rise to a slow-glow kind of flashing visual over the connected lamps

5) Here the lights are switched off and ON with a chasing and simultaneously flashing style.

6) A quick switch ON of the lamps but a slow-fade effect can be witnessed in this position

7) The 7th preference produces a twinkling flashing effect on the lamps quite resembling the stars on the sky.

8) In the last mode the lamps actually do nothing but light up solid ON which also sometimes becomes useful for certain decorative applications.

For using the above circuit with high watt AC lamps, the design could be modified in the following manner:

Courtesy: search.alkon.net/cgi-bin/pdf.pl?pdfname=utc/8156.pdf

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!