Heart rate meter project (pure hardware circuit)

Heart rate meter engineering precautions

The current version is explained in detail, and the second version has not been tested yet. The debugging method of the first version is the same as the second version, so both versions can be referenced. The circuit diagram of the first version will not be shared.

The circuit diagram you see below is the circuit diagram that has been upgraded to the second version. Please feel free to use it.

This project started on December 14, 2020. It took a total of 40 days to complete the first version of debugging. Many of the components needed to be ordered, so I had to wait for more than 20 days for express delivery.

The final test of the second version will be conducted some time after the Spring Festival in 2021

(Too many things)

. . . . . .

1. Device selection part

        Since I still have the TL074P chip left, I have not purchased it in the above list. If you don’t have this chip, please remember to purchase it . Please note again that the requirements for the CD4027 chip in this project are very high . The domestic CD4027 chip cannot meet the requirements of this project. You need to select the MC14027 chip produced by the Korean Philips Company . Otherwise, you will find that the digital tube cannot be cleared after counting and will keep accumulating ( Since the frequency requirements of domestic chips cannot be met), the remaining components can be selected by default (resistors, capacitors, etc.)

2. Welding precautions

        It is especially recommended to solder the side with more components on the back of the circuit board first. Due to limited conditions, I chose hand soldering . If possible, you can use a heating table with solder paste.

(1) Solder the short components first (devices that will not affect the soldering of other components after the welding is completed)

(2) Secondly, the rest of the devices (it was found that 3 chips of the same model were packaged incorrectly) (this is the first version)

(3) Soldering these three incorrectly packaged devices (first version)

(4) When welding plug-ins, the following should be noted:

                (A) Before welding

                (B) After processing

(5) After the welding is completed (do not weld the TYP-C socket at H1 first, weld the power cord for testing first, if the test is successful, then remove the power cord and weld the TYP-C interface)

3. Debugging Precautions

        (1) Complete the calibration work according to the following requirements

                     Adjust RP1 so that the frequency of TP1 is 666Hz.

                     Adjust RP4 so that the frequency of TP5 is 40kHz.

                     Adjust RP2 so that the frequency of TP2 is 1Hz.

                     Adjust RP6 so that the frequency of IC25_3 is 10Hz.

                     Adjust RP5 so that the voltage of TP6 is 2V.

                     Use an oscilloscope to measure TP3, and use RP3 to adjust the voltage of pin 2 of U5.1, as shown in the figure below. ( The voltage of pin 2 of U5.1 is equal to between A and B )

                         LED (LED1~21) displays the heart rate waveform.

                         example 1)

                         Example 2)

 

                         7-segment LED (LED1~3) displays BPM.

4. Description

        (1) After the testing of version 2 is completed, the shell will be printed using 3D printing technology

            (2) The video material is the effect presented in the first version. If you observe carefully, you will find that the flow direction of the second row of LED lights is opposite to the flow direction of the upper and lower rows of LED lights. This is because the light sequence was not placed correctly when drawing the LED lights in version one. Caused by the fact that version 2 circuit board has been modified and functions normally

            (3) The display of the digital tube in the video is abnormal and keeps accumulating. This is caused by the chip used not meeting the requirements. This has been explained before. Please note that

            (4) The debugging and testing instruments used in this project mainly include dual-channel oscilloscopes, DC regulated power supplies, multimeters, etc.

            (5) The second and final version will be arranged as soon as possible

            (6) Others