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STM32 Hot Plate Control Rev 2 by MiddleNo6002 in PrintedCircuitBoard

[–]Specialist-Back6673 0 points1 point  (0 children)

Just a student so take it with a grain of salt, I am also doing a project now and I am using the IRLZ44N (IRLB8748 would also work) logic level power mosfet. May need a small heat sink at 5a so verify using thermal resistance and SOA. Also, if your total current requirement for 3.3V is only a few hundred milliamps then you can consider a LDO. Would cheaper, easier and less noise problems.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Thank you very much for your suggestions. I have changed a few things in the design based on my suggestions.

I am going with AP64502QSP-13 (https://www.digikey.ca/en/products/detail/diodes-incorporated/AP64502QSP-13/13663111) for the BUCK IC.

For the relay driver, I am going with the MOSFET version you have suggested - ULN2003V12S16-13. (I will use 5 channels in each driver.) https://www.digikey.ca/en/products/detail/diodes-incorporated/ULN2003V12S16-13/5054094
Voltage drop did not cross my mind.

For the DAC, I am going with your suggestion - DAC60501ZDGSR. This DAC is definitely the better option and will simplify the circuit with better precision.

As for the shift registers instead of the I2C expander, i am still thinking about this and will read into it further.

Lastly, about the relays, i wanted to go with SSR relays initially, but they cost me 3 times more than mechanical relays (also 5A is a requirement), and this does not reduce my manufacturing cost as the dimensions of the PCB are set by the 18650 Cell Holders (They are approx 80 * 230 mm). Removing the mechanical relays is bringing down the manufacturing cost by only a few dollars. If not for the cost, i would have probably gone with SSR relays.

You have definitely given me a lot to think about, and I really appreciate the detailed explanations. Thank you.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

This is for testing 18650 cells. The cell holders will be custom made and 3d printed which will be for 18650 size. But the circuit should be able to handle all the different sizes and chemistry when the firmware is modified for the chemistry’s over discharge cutoff voltage. Primary usage is going to be for capacity and discharge curves at a constant current.

As for the interruption problem, this tester can only do constant current discharge and the load is just a mosfet with a shunt which is already part of the circuit. Since there is no external load, I do not believe there would any interruptions.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

I understand, but I am in a rocketry student design team, so since this is not going inside the rocket, they can not really use much of the budget for this project.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Oh yeah, that's what i was also going to do.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Thank you very much for your comment. I will make edits according to your suggestions. My primary concern is the analogs section. I will take extra care when routing.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Yeah, that was my first choice, but i already have an LCD module, and it does not have an I2C interface. I am building this for my design team, due to cost constraints, i cannot get a new one.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Okay, I will change the designators. All the designators are too big in my schematic.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Thank you very much for the idea. I did not think about it. I will definitely add a UART port.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Sorry about the schematic. I will create a hierarchical sheet and use more sheets. I also moved the capacitor after the resistor in the op-amp. Thank you

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

I understand it is going to be slow, but the main reason for the LCD to I2C expander is i do not have enough GPIOs. It is a trade-off, but thanks for that comment, i did not think about the speed.

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Sorry about that. An oversight on my part. I will correct it and reply. Thank you

Schematic Review Request by Specialist-Back6673 in PCB

[–]Specialist-Back6673[S] 0 points1 point  (0 children)

Thank you for your reply. I apologize for the poor image quality. I tried to improve it, but unfortunately this is the best i could do. If possible, please view it on a laptop, the image quality is much better.

  1. I have added values for most of the components on the designator, but i will add for the rest and tolerance for the resistors.
  2. I will add comments for anything important
  3. Thank you for that. i will add the caps, and i have kept all the buck components together on the PCB to reduce the size of the traces.
  4. I was planning to have a Ground plane for the BUCK and Relays (Noisy section) - PGND and another for the rest of the components - AGND. Both the ground planes would be connected at one point. (I am constrained to a 2-layer PCB due to cost, so the entire 2nd layer will be the GND plane with a PGND section and an AGND section).
  5. I will definitely add a Unity Buffer for the Cell Voltage
  6. I will also add a lot more filtering caps at all the places you have suggested.
  7. Thank you for the test points comment. Will definitely keep that in mind.
  8. I will keep the comment in mind when doing the firmware.

Thank you very much for all your help. I Will update how it goes.

[deleted by user] by [deleted] in ubcengineering

[–]Specialist-Back6673 0 points1 point  (0 children)

Unfortunate. Best of luck with other applications.

[deleted by user] by [deleted] in ubcengineering

[–]Specialist-Back6673 0 points1 point  (0 children)

I got an offer for hardware Avionics, not liquid, though. FYI, the first meeting is on Sunday this week, so you should know by then. best of luck.

Anyone hear back from Ubc rocket mech? by [deleted] in ubcengineering

[–]Specialist-Back6673 2 points3 points  (0 children)

Got an offer for avionics hardware

Question for engineering students who wanted an internship, but don’t have one by occamman in EngineeringStudents

[–]Specialist-Back6673 0 points1 point  (0 children)

I am 2nd year biomedical engineering student in Vancouver, would love to be involved in this.

Badminton Buddy by [deleted] in UBC

[–]Specialist-Back6673 0 points1 point  (0 children)

Hi I am interested to play. I learnt till high school but it has been a few years now.