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This € 7.23 kit gives you a PCB that alternately shows the time and temperature on seven-segment displays and the seconds on sixty rotating LEDs. |
Introduction to the rotating LED clock
The end result
Imagine a clock that not only tells the time and temperature but also transforms every second into a visual experience. With a compact eight-by-eight centimeter PCB, four seven-segment displays, and a ring of sixty LEDs, this unique timepiece offers more than just functionality. It alternates between showing hours, minutes, and temperature in degrees Celsius, while the LEDs, arranged in a perfect circle, track the passage of time with six dynamic scenarios.
For those looking to add a bit of flair, the clock also includes four additional psychedelic patterns that can be activated with a few button presses. One pushbutton allows you to program the time, while another lets you select from ten visual scenarios, making the clock as customizable as it is captivating. Plus, with its auto-dimming function, the clock dims softly when you go to sleep, so it’s easy on the eyes in the dark.
Manufacturer, suppliers and price
The manufacturer of this kit cannot be traced. What is clear, however, is that various versions are offered. For instance, there are kits where the DS1302 chip is supplied as a DIL-8 and kits where this chip is present as an SMD component. We ordered one with the SMD version via AliExpress from the 'Huisheng Dongye Store' for € 5.09 plus € 2.49 for a plexiglas case. Shipping costs € 1.99.
Delivery of the package
The components are packed in a plastic bag, with the displays, processor and IC socket pressed into pieces of Styrofoam. So the pins cannot bend during transport.
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| The packaging of the components. (© AliExpress) |
The delivered components
All the parts supplied are presented in the picture below. There is nothing to comment on.
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The delivered components. (© 2024 Jos Verstraten) |
The manual
In the package is one sheet of A4 with some Chinese text and a scan code to https://bennuhp.blogspot.com/2019/08/led_27.html. This is a Chinese Google blog with remarks on Chinese kits. You won't get much wiser from this Google page, it is nothing more than the translation of the sheet of A4 in the package.
The circuit board
In the picture below, you can see both sides of the 8.0 cm by 8.0 cm PCB. The quality of this PCB has nothing to complain about either.
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Both sides of the PCB for the circuit. (© Huisheng Dongye Store) |
The schematic
The figure below shows the full schematic of this kit. On the top right is the buzzer SPEAKER, which is driven from one of the microcontroller's outputs via the transistor Q1. Below that, you can see the input of the 5 Vdc supply voltage (DC002 and B), which is decoupled by capacitor C3. RM and GM are two sensors. The thermistor measures the temperature, the LDR the amount of ambient light. The temperature sensor provides the data for showing the temperature on the display in °C, the LDR is for adjusting the brightness of the displays.
To its right is the microcontroller type STC15W408AS from China's STCmicro. This is an improved version of the well-known microcontroller 8051. This microcontroller works with an internal clock, no external crystal is needed.
On the bottom left is the beating heart of the circuit. The DS1302 is a real-time clock generator. It provides date and time data in the form of the current seconds, minutes, hours, day, month and year with even leap year compensation up to the year 2100. In this building kit, only some of the capabilities of this IC are used. This IC is controlled from a crystal Y1 oscillating at 32.769 kHz. You can connect a 3.3 V button cell to pin 8, so that the clock remembers the time and date even if you interrupt the 5 Vdc supply.
Pushbutton S1 allows you to programme the clock, while pushbutton S2 selects from one of the ten scenarios used to control the sixty LEDs.
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| The diagram of the clock. (© Huisheng Dongye Store) |
Building the circuit
Assembling one side of the PCB
The recommended order, from small to large, is:
- The DS1302 SMD chip.
- Eight resistors of 330 Ω, in our package there were ten supplied.
- Three resistors of 10 kΩ, in our package there were five.
- The temperature sensor RM, which is the small black part.
- Two capacitors of 10 pF (notation 10).
- One capacitor of 100 nF (notation 104).
- The LDR resistor GM, which is the almost round white part.
- The 32.769 kHz crystal, this should rest flat on the PCB.
- The IC socket for the microcontroller.
- The holder for the 3.3 V button cell.
- The transistor S8550, note its correct position.
- The mini-USB connector.
- The buzzer, note the plus and minus here.
- The two pushbuttons S1 and S2.
The photo below shows this side of the PCB with all components soldered to it.
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| The fully soldered component side of the PCB. (© 2024 Jos Verstraten) |
Assembling the other side of the PCB
On that side, mount the sixty LEDs and the seven-segment displays. Start with the twelve red LEDs. The longest connecting wire is the plus, it comes at the edge of the PCB. Push the LEDs fully into the PCB until they rest on the surface, making sure they are neatly straight. Continue with the 48 blue LEDs, which you mount in an identical way. Both the red and blue LEDs were supplied with a few more than necessary. Finally, solder the seven-segment displays. Pay attention to the position of the decimal points here!
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| The LEDs and displays assembled. (© 2024 Jos Verstraten) |
Final assembly
Very carefully push the STC15W408AS into the IC socket, paying attention to the correct position. Before applying pressure to the IC, check that all pins are really in the contacts of the socket. Mount a CR1220 button cell in the holder. Again, make sure the cell is correctly positioned, with the plus at the top of the holder.
Working with the clock
The power supply
You can power the clock from a 5 Vdc mains power supply via a USB-A to mini-USB cable. You can of course also make a power cable from a USB-A cable to the two pads 'PWR' on the PCB, above the USB connector. Here, of course, pay attention to the plus and minus. In a USB-A cable, the positive pole of the power supply is on the red wire and the negative pole is on the black wire. The green and white wires are for transporting data and are not necessary here.
When you switch on the power supply, the seven-segment displays will indicate a random time and the LEDs will light up one by one in a one-second rhythm.
Selecting a scenario
You do this by pressing the pushbutton S2. Ten different light patterns have been programmed into the processor. You can see these in the video with which this article begins.
Programming the clock
By pushing the pushbutton S1, you can programme the clock. After each push on this switch, you can use pushbutton S2 to set the value of the selected parameter.
- First push on S1:
Setting the minutes of the current time. - Second push on S1:
Setting the hours of the current time. - Third push of S1:
Setting the minutes of the alarm time. - Fourth push on S1:
Setting the hours of the alarm time. - Fifth push on S1:
Setting the alarm function. The display goes to '00.00'. This means the alarm function is not active. After pressing S2, the display becomes '11.11', this function is activated. You deactivate the alarm by briefly pressing S2. - Sixth push on S1:
Setting the dimming function. The display goes to '00.00', this function is not active. After pressing S2, the display goes to '11.11' and this function becomes active. As the intensity of the ambient light decreases, the intensity of the display and LEDs also goes down. - Seventh push on S1:
You exit the programming function, the current time is shown on the display.
A printable housing
For this clock, Philip Schwartz designed a housing that you can reproduce with your 3D printer. The necessary files can be found at:
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The housing designed by Philip Schwartz. (© Philip Schwartz) |
The accuracy of the temperature indication
There is no possibility built in to calibrate the temperature indication. In the kit delivered to us, the indicated temperature was found to be within ±1 °C equal to the temperature measured by our room thermostat.
The accuracy of the time indication
This is excellent; after one week, no deviation from the official time was detected. This is not so surprising, as the combination of a 32.769 kHz crystal with the DS1302 chip is used in billions of cheap wristwatches and they all work quite accurately.
Rotating LED clock kit
