# Fifth Lichuang Electronic Design Competition# Data gloves with pressure feedback

team introduction

Our team members are all members of the 402 Laboratory of Shenzhen University, and they are each responsible for the division of labor in the structure, circuit, program and other directions.

Project Overview

The characteristics of this project are very clear from the name of the project, which is a data glove with pressure feedback. The so-called data gloves are gloves that collect hand motion information through sensor means. After processing, this motion information can be used for many purposes, such as gesture human-computer interaction, input control, motion capture, etc. Our project is to add a pressure feedback design to such a glove. Specifically, air bags installed on the fingertips are inflated and deflated by an air pump to achieve pressure feedback by squeezing the fingers. With such feedback, the data glove can optimize the experience in each application direction mentioned above.

Project details

overall system

The picture below is the system block diagram of this project.

The left half of the picture above is the hardware end, and the right half is the host computer end. In this project system, the microcontroller collects the data of each sensor on the glove and the Bluetooth serial port module sends the information to the host computer. On the other hand, the microcontroller also receives The instructions sent by the host computer control the air bag pressure in real time to form feedback, and the host computer mainly realizes the presentation of data and some simple applications.

software key

In the software design of this project, the key points are the air bag pressure control by the microcontroller and the programming of the host computer. 1. Airbag control algorithm. Because we need to maintain a certain pressure in the airbag, we use a barometer to write a closed-loop algorithm inside the microcontroller when controlling the airbag. We adjust the air pump power in a timely manner through feedback, so that the airbag can quickly respond to instructions on the one hand, and on the other hand. On the one hand, it can also resist external pressure on the air bag. At the same time, the bending sensor and attitude sensor on the glove respectively return the bending degree information of the fingers and the attitude information of each joint of the palm. This information is sent to the host computer via Bluetooth, so that a virtual hand can be simulated on the host computer. 2. The host computer is designed based on the Unity3D game engine. It provides some physical effects and collision monitoring functions, which is very suitable for this project. Because there is a universal lock problem when using Euler angles to represent rotation, we spent some time understanding the rotation representation of quaternions. It just so happened that untiy itself supports quaternion representation of rotation and provides a suitable library. Our main design on the host computer is how to combine the various data obtained and finally restore the appearance of the data glove in reality. First, we built a hand model, designed the connection relationship of each joint, and mapped the quaternion data of the mpu6050 of the palm and thumb to the corresponding joints to realize the rotation of the relevant parts. The data of the remaining fingers are sampled by the bending sensor, and the data are converted into bending angles to complete the display of finger bending.

Hardware key

1. Air pump power supply circuit: Two MP1584 switching power supply step-down chips are used to reduce the 12V to a 5V power supply that can be used by the air pump. Since the number of air pumps and solenoid valves used is large, the power and current are large, so the maximum current of the power supply needs to be Only the larger one can ensure the perfect function of the circuit. An MP1584 chip can output a current of less than 3A. Two switching power supplies can increase the output current of the power supply, but the output 5V cannot be simply connected in parallel. This will cause one of the power supply chips to not work or burn out, so use the diode SS54 to prevent current backflow. The figure below shows the power supply selection of the air pump and the switching power supply circuit to prevent backflow.  2.  Chip power circuit: **** Use ME6219C33M5G to reduce 5V to 3.3V for use by the main control chip.

3. The air pump and solenoid valve are driven     by LNSC2302. The air pump chooses a 5V DC air pump, and the solenoid valve is also a 5V three-way solenoid valve. There are two original solutions. One is that one air pump corresponds to one air bag, and the air bag is controlled by controlling the air pump. air pressure. The second is that one air pump corresponds to several air bags, and the air pressure of the air bag is controlled by controlling the solenoid valve corresponding to the air bag. At first, I bought two types of DC air pumps, 3.3V and 5V. After actual measurement and experience, I found that the 3.3V air pump I bought vibrated violently when supplying DC power, and the air flow was unstable, causing the airbag to vibrate violently and give a poor experience. 5V air flow is smooth, so choose a 5V air pump. Since the weight of the 5V air pump is relatively large, the weight of five air pumps is a bit too heavy, and it also takes up more space, so we will try the second option first. After testing, it was found that the solenoid valve is not effective in controlling the air bag pressure. Since the solenoid valve is a physical switch and directly deflates, the air pressure in the air bag changes drastically, making it difficult to achieve a stable and controllable state. Finally, Plan 1 was adopted, using an air pump to control the air bag one-to-one. When the glove touches an "object" in the host computer, the air bags on the fingertips will expand, causing the fingers to feel different pressures. When the gloves do not touch the object, the solenoid valve will deflate, the air bags will deflate, and there will be no pressure on the fingers. Thus achieving the effect of gloves with feedback.

4. The main control chip is STM32F407VET6: When using STM32F103C8T6 in the first version, it was found that the number of frames of the host computer was too few, the refresh was too slow, and it was relatively laggy, so this time the STM32F4 chip was used

5. Six-axis : It is divided into six axes on the wrist and six axes on the back of the hand. An additional six-axis interface is reserved on the fingers. It can be used with IIC using different addresses.

6. Bending sensor: After consulting the information on the Internet, there are two solutions. You can directly use the ADC inside the chip, and then read the voltage value of the bending sensor by dividing the voltage to obtain the bending degree. The second option is to add an external ADC circuit. Since adding an external ADC circuit would occupy too much area on the circuit board (5 ADC modules need to be drawn because there are 5 fingers), the first option was chosen. Based on the circuit diagram provided by Taobao, I drew a version of the PCB (picture below).  During the actual measurement, I found that the data fluctuated very much and the data could not be used. After using software filtering, although the data became smoother, the reading frequency became lower again, which would cause the host computer to The model delay< span class="size"></span> later added a capacitor to implement physical filtering. After many capacitor replacement tests, it was found that the 10uF capacitor worked very well and solved the problem of large data fluctuations. The improved circuit is as follows < span class="size"></ /span> 7. Air pressure detection circuit: Use the XGZP6847 0-40KPA module and use the ADC pin of the main control chip to measure its output voltage, thereby knowing the internal air pressure of the air bag. Together with the air pump drive and the solenoid valve drive, the air pressure of the air bag is controlled to provide feedback to the fingers so that the fingers can feel the pressure. The Bluetooth module is HC08: This module can send and receive data. There is a Bluetooth on the glove end and a Bluetooth on the computer end to connect the CH340 to send data to the computer. Circuit board PCB 3D drawing

Project photos

Video station B link

Team introduction: https://www.bilibili.com/video/BV1hC4y187ak Project introduction: https://www.bilibili.com/video/BV1Hf4y1R7mi Project demonstration: https://www.bilibili.com/video/BV1Hf4y1Q7kM?from =search&seid=153764277043774185