Adjustable desk lamp

I. Introduction

This year’s electric competition has been postponed and postponed again and again, but this also gave us more time to prepare. I didn’t even go home during the summer vacation. I have been studying spherical cars and electromagnetic knowledge until the competition started. I found, , all the preparations were in vain, and were not used; the cancellation of the comprehensive evaluation resulted in the comprehensive evaluation circuits prepared in advance being completely useless. After the competition started, as a circuit engineer, I chose the topic of table lamps. After the day and night efforts of several members of the team, I finally won the first place in the country. I would like to share my work with everyone!

2. Team introduction

Team members: Song Aohui, Xu Shipeng, Wang Shuaidi

Instructor: Ni Peng 

The members are all members of the Electronic Control Laboratory of the Mechanical and Electronic Innovation Association, College of Applied Technology, Changchun University of Technology

3. Topic analysis

Design and produce an LED desk lamp with stable and adjustable illumination and a digital display illumination meter. The dimming desk lamp is composed of an LED light panel and an illumination detection and adjustment circuit.

1. basic requirements

(1) The digital display illuminance meter is powered by a battery. The relative illuminance digital display is no less than 3 and a half digits and does not require illumination calibration. The detection head of the digital display illuminance meter is placed 0.5 meters directly below the dimming desk lamp. Adjust the brightness of the desk lamp. When the maximum illumination is reached, the display number is greater than 1000; when the detection head is blocked and reaches the minimum illumination, the display number is less than 100. When the brightness of the desk lamp changes continuously, the digital display also changes continuously. When the brightness is stable, the digital display is stable and the jump is no more than 10. There cannot be any exchange of information between the digital display illuminance meter and the dimming desk lamp.

(2) Dimming table lamp input voltage Vi: DC 10V ~ 15V, changes in Vi do not affect the brightness.

(3) The brightness is continuously adjustable from the brightest to completely extinguished, without flickering (the LED light panel power supply voltage ripple is less than 5%). (4) When the power supply voltage of the desk lamp is 12V, the power efficiency (the ratio of the power consumption of the LED light panel to the output power of the power supply) is not less than 90%. 

2. play part

(1) Adjust the desk lamp to the maximum brightness, and place a piece of A4 white paper 0.5 meters below it. The brightness of the entire area of ​​the white paper is required to be uniform and stable, and the illumination difference at each point is less than 5%. There can be multiple illumination detection heads of the desk lamp, located at any position other than the A4 paper.

(2) Use another LED light panel adjusted to maximum brightness as the environmental interference light source for testing, and change the distance to achieve changes in interference light intensity. When the ambient light changes slowly, the duration of the weakest and strongest changes is not less than 10 seconds. The desk lamp can automatically track the changes in ambient light and adjust the brightness to keep the illumination change in the center of the paper no more than 5%; when the ambient light suddenly changes, the duration of the weakest and strongest changes is not less than 10 seconds. The change duration is no more than 2 seconds, and the sudden change in illumination in the center of the paper is no more than 10%. When the ambient light increases until the desk lamp goes out, the illumination change in the center of the paper is no more than 10%.

Alas, after playing with lanterns for several years,,, finally gave up,,, here we go again,,,

4. Composition of the work

The work is mainly composed of LED light board, Arduino nano development board, mini360 buck module, IIC LCD1602 liquid crystal screen, LM321 operational amplifier, BH1750 illumination sensor module, etc.

5. Overall block diagram:

The functions of each module:

LED light board: We mainly use 3.3V LEDs with a power of 1W. Due to time constraints, we directly welded an LED light board with a perforated board. In order to solve the heat dissipation problem, we used all the voltage reduction work without considering the heat dissipation problem at all. , the actual power of each LED is about 10%--20% of the rated power. Although it causes a waste of power, it has ultra-high light efficiency. The LED light panel adopts a multi-area individually controllable solution, and several low-power LED lamp beads are set up as fill-in light, which greatly improves the uniformity of illumination.

 Main control: The Arduino nano development board is used as the core control board. The main reason for choosing it is that our laboratory has sufficient inventory of this thing, so we don’t have to waste precious competition time just to buy it, and the function speed fully meets the requirements.

mini360 step-down module: Two mini360 modules are used, one is used to step down the power supply for 5v devices such as microcontrollers, and the other is used to provide constant voltage power supply for LED light panels; this module uses the MP1584EN high-efficiency voltage conversion chip, which is adjustable. Isolated buck chip, the maximum output current can reach 3a. We have optimized the circuit design, the ripple can be stably controlled within 2%, the efficiency can reach up to 95% or more, and the cost is low, only 2-5 per chip Yuan.

IIC LCD1602 LCD screen: The screen using the IIC interface not only saves the screen's occupation of the I/O port, but also reduces the workload and saves time; among them, we specially modified the 1602 to IIC adapter board to reduce the brightness of the LCD backlight to improve the overall The working efficiency of the equipment (although it cannot be reduced much, it can be reduced if it can be reduced)

LM321 operational amplifier: used for lamp board current signal sampling and amplification, I originally chose TP09, but found that the withstand voltage was too low (only 6V) and was easily burned by voltage spikes. Later I chose lm321, which has high withstand voltage and low power consumption. Low and cheap. (See the lm321 with two solder joints in the picture, it’s too small, haha)

Sensor: The light sensor uses BH1750, which has high precision and comes with built-in filtering. It can be used directly and is cheap, about 7 to 8 yuan a piece.

The display screen of this work can display the current, voltage, power and other data at the lamp board end of the desk lamp in real time. The voltage signal is sampled by a resistor, and the current signal is sampled by the resistor. It is filtered by a two-stage low-pass filter. The current signal is amplified by LM321, and the output is filtered again. The data are all measured using a multimeter. It has been verified and calibrated with an oscilloscope (we only have a multimeter and oscilloscope that can be calibrated here, there are really no better instruments, and the oscilloscope and power supply are from the laboratory decades ago)

Current and voltage sampling resistor section Amplification and filtering section

The actual objects are as follows:

(Oscilloscopes and power supplies from decades ago in the laboratory )

The actual consumption of the entire work is probably less than 300 RMB (excluding power supply and instruments, etc.).

The code is written for Arduino IDE and requires the use of three libraries, namely IIC library, soft serial port library, and IIC to LCD1602 library. These are standard libraries and can be easily found and downloaded online.

The specific code can be downloaded from the link below.

Program source code: https://wwi.lanzout.com/il2avxz1zti

This work is the K question of the Higher Vocational Group of the 2021 National College Student Electronic Design Competition. It is a table lamp with stable and adjustable illumination.

Schematic diagram

The overall picture of the table lamp part, and the divided pictures are all included. You can enlarge them for a closer look.

General picture of the illuminance meter, one picture is everything!