First of all, I would like to thank the forum platform for providing us with such good resources. I haven't participated in forum activities for a long time. This time I happened to be making a small tool, and the chip I evaluated happened to be useful, so I participated.
The demand was this: we were making the microphone chip for the electronic cigarette, and it needed to be tested. It would be troublesome if someone had to inhale it every time, so we wanted to find an alternative solution. Later, we saw from the customer that a vacuum pump and a straw would do the job.
Water pump parameters: DC6V, 0.6A, <5W, positive pressure: 0.045MPa, negative pressure: 0.035MPa;
Then I had an idle 12V lithium battery
So I came up with the following idea:
The following is the implementation problem. I use the CH224K I got this time to generate 12V to charge the lithium battery. I tested the lithium battery charging with a power supply before. The charging current is about 200mA. As long as the charger supports 12V output, there is no problem charging the lithium battery. The next step is to choose a DC-DC converter. I chose a DC-DC CR3202 from the company. This IC is compatible with BL9342, ME3116, etc., and has one less freewheeling diode in the BOM. When designing the schematic, I made a compatible design, and all three materials are OK. The designed schematic is shown below:
The PCB diagram is as follows:
3D Preview
After the board is back, start debugging.
After I came back, I measured that VBUS always output 5V, then I modified the CFG resistor, the resistor connected to VBUS, and after changing the chip, it still output 5V. However, the output on the EVB KIT was normal, and I checked the connection relationships and found that they were not disconnected. I kept refreshing the chip manual, but still found no problem. Then I connected an oscilloscope to see the waveforms of DP and DM to see if there was a problem with the enumeration. By comparing with the waveforms of EVBKIT, I found that the waveforms on DP and DM seemed to be repeatedly enumerated (as shown in the figure below). Finally, I found that my DP and DM lines were connected in reverse. At the same time, I saw a message in the manual that CC1 and CC2 were cross-connected with CC1 and CC2 on the connector. It is not CC1 connected to CC1, and CC2 connected to CC2.
The following is to verify whether the problem is correct. The DP and DM cross-fly wires are
After the flying line is completed, the 12V output is tested to be normal. Below is the measurement video.
WeChat_20220824232509
Below is the finished product based on my idea. Just wrap it with tape and it will be OK.
Finally, I will show you a video of water absorption. It is quite convenient to use. If you want to test it later, you just need to turn on the switch.
吸水
The current hardware needs to be modified:
1.DP and DM lines need to be corrected;
2. The PCB board and the vacuum pump are loose when welded. It is best to leave a hole in the middle so that the protruding part of the pump shaft can be embedded in the PCB board, so that it can be fixed more securely.
3. Now there is only a working indicator light for the pump, and a charging indicator light needs to be added. The PG pin of CH224K should be able to meet this function.
The subsequent design adds some functions:
1. Consider adding an MCU control output to see if it can be compatible with more batteries;
2. Add an air pressure sensor to display the current pressure value;
3. Add some mass production test functions;
4. Consider making a shell to increase aesthetics.
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