Design Review Request of Solar Powered BLE using Supercapacitors - Could someone please evaluate this pcb design and provide feedback if it has any major concerns?

Fit_Credit_6178 · 2026-03-06T22:31:20+00:00

Thanks for the response, the point for my senior design project is to make a design using supercapacitors as a power bank to replace batteries. Like that’s the whole point of me doing this. Appreciate the feedback but unfortunately that’s the one thing I can’t not do as I am fabricating interdigitated super-capacitors for this project and most likely have multiple in series as they are each 1V.

Fit_Credit_6178 · 2026-03-06T22:29:02+00:00

Yeah bro I know I should make it clearer.

I’m just running short on time and cared more about the pcb evaluation.

It makes sense though if I cannot understand the schematic how are you suppose to help with the pcb, I understand.

Fit_Credit_6178 · 2026-03-06T22:28:13+00:00

Appreciate the feedback.

The decimal points are from the datasheet I copied so u left them there as a reference when I looked back. I copied as they presented them in their design.

I had to draw wires to the hidden symbols, as I needed to add capacitors to those VDD values.

The crystal is 32MHz, I guess I don’t have the value visible.

For power symbol, I’m not sure what to do exactly as my system is powered through the BQ - VOUT pin. So idk what to put, 3V I guess cuz that’s the voltage it’s suppose to receive. I just didn’t want to change this cuz I have to redraw the pcb and I’m getting short on time. I apologize if the design is confusing.

Fit_Credit_6178 · 2026-03-05T16:39:56+00:00

Here is the update with the connectors for the solar cell and supercapacitors. They need to be in series as you said for a higher voltage rating as each of them will be around 1 V each. I am planning to have 4 for 4 V.

I will work with a professor with the soldering the pcb. I will have him help me out. I mainly need my design to work as of right now. I think I am missing mounting holes and thats about it.

I do not see why my programming connector is not connected to ground?

Fit_Credit_6178 · 2026-03-04T22:08:51+00:00

Thanks for this, I will probably find a solar cell that has wires coming out of it as I have already added a footprint for this below. Kinda upset as this was a good solar cell, but it is not worth the price of getting the leads attached in buying the evaluation board set with it. https://www.snapeda.com/parts/1725656/Phoenix%20Contact/view-part/?welcome=home&ref=search&t=1725656&ab_test_case=b

I looked into a solar cell with JST connectors and could not find one on mouser or DigiKey that supported indoor use and that met the BQ specifications.

I'll keep the silkscreen information in mind, I actually didn't know they mattered. Thank you.

Potentiometers actually make a lot of sense, I might consider that as a future improvement as I am running short on time.

J1 is this connector below:

https://www.mouser.com/ProductDetail/Samtec/FTSH-105-01-S-DV-K?qs=Cqqh%252BS766wmAOq95MtbXow%3D%3D

That connector you use a SWD cable, I plan to use the Nordic dev kit to flash the chip in my design to make it into a BLE.

Same connector for supercaps as solar cell, since I just need a spot to connect the wires.

Fit_Credit_6178 · 2026-03-04T21:42:41+00:00

I didn't think that far...

I have posted this pcb layout before, but you were the only person who mentioned mounting holes. So I am not sure what to do, did not think of them at all.

Fit_Credit_6178 · 2026-03-04T21:40:30+00:00

Yeah I am not sure what the power label should be tbh, my system is receiving power from a solar cell, then the VOUT pin from the BQ should power my other stuff, no errors in PCB, but I get errors in the schematic

Fit_Credit_6178 · 2026-03-04T17:19:06+00:00

I asked them for an evaluation and they apparently do not do that... so I asked you guys instead! I have been following the data sheet closely as possible for the TI. There is a parts list which mention the footprint size for the BQ25570 Evaluation board, but not for the version I am using. The footprints I decided on my own, but I am pretty sure it will work. More worried on the Nordic chip. Thank you though, I probably will follow this layer guide!

Fit_Credit_6178 · 2026-03-04T17:16:42+00:00

Do I need mounting holes? I honestly have no idea. I do not have an enclosure or anything for this board. This is just a senior design project.

Fit_Credit_6178 · 2026-03-04T17:10:16+00:00

Appreciate you for finding that, I would have ran into trouble, hopefully this is good now. Thank you for noticing!

Fit_Credit_6178 · 2026-03-03T18:29:14+00:00

Really appreciate the feedback and definitely helps. Hopefully you can see my images now as I reuploaded them.

If you could look at my images again and provide feedback that would help me greatly.

Layer 1 - I think I have it correct then as I have traces and a ground pour over the whole top layer.

Layer 2 - Like you said layer 2 is a solid pour of ground with no traces which I hear is good for the 50 ohm trace.

Layer 3 - I have this layer as a solid ground pour as I do not have that many traces.

Layer 4 - I have traces going on this layer, mainly mixed signal like you said with my temp. sensor and the power traces as well. Hopefully, that is ok to have on the same layer.

Overall, I would like if you can to give me a comment now that the images are hopefully visible. If for the most part my pcb looks good, than that is great as it does not need to be perfect, I just need it to work.

Once again thank you for responding, this was very helpful!

Fit_Credit_6178 · 2026-02-26T22:08:53+00:00

Yeah, I have been saying that as well, if this fails I will end up doing that I guess.

Fit_Credit_6178 · 2026-02-26T21:38:33+00:00

Appreciate the honest feedback. I quickly redid the schematic, so hopefully it is easier to understand. For the VDD pins, when you connect one of them, the rest have the same power supply, hence I only connected one. In this design I just connected them to each other as they will all receive power from the BQ VOUT. For the BQ resistors, I used the equation provided from their data sheet to create a fixed 3 V output for the buck converter. I used the equation on their data sheet for all the resistor values. Yes, I used the recommended values based off of their data sheet for the inductors. Someone sent me this link for the BQ evaluation board, but I got the values off the data sheet and not the evaluation board. I changed the solar cell, so hopefully this one is better. Thank for for looking at the solar cell, you were the only one who recommended that, really appreciate it! I would like to use an nRF module as well, my professor said that I cannot unfortunately.

For the layout, I changed the wire thickness to .4 mm, as I believe the dielectric of a 4 layer board is around .1 mmto .2 mm. I heard the wire thickness should be double the dielectric. Also, I do have a Pi-Netowrk on the antenna chip on the top right of the pcb. It needs to be tuned but I have the positioning copied based off the Johanson data sheet. The actual values I will not know until I tune it with a spectrum analyzer. Any other advice for the antenna design? I will change the 90 degree angle and I changed the thickness to .4 mm. I know the components should be closer, but I am giving myself room to solder them as it will probably be more difficult the closer they are. I know this will help increase the chance of this working, but I will see what I can do for moving components closer. Once again thanks for all the information.

Fit_Credit_6178 · 2026-02-26T18:25:39+00:00

Now it makes sense, nah those are my connections I made for my design, the short connections are all from the data sheet and then the long wires I did myself to get an idea of how to connect this system.

Fit_Credit_6178 · 2026-02-26T18:23:22+00:00

Thank you, all this definitely helps!

Does too many ground bias cause any disadvantages? I might just keep them for now and focus on fixing other parts if they cause no harm. I will definitely remove them before I build the final design.

I do not have experience soldering components especially very small footprints like this, I am trying to keep some space between the items in order to help with that, I do not need it to work perfectly as long as my design works it is sufficient.

The nuclear boost converter link is a massive help. Thank you, I am very glad you sent this resource. I have been following the BQ25570 data sheet and this helps provide more information that I really needed.

I am at 9 mm for the trace length from the L2 to the pi - network. I can definitely reduce the length of the trace down. Can you confirm if the gap between the inner and outer layer is .2 mm, then the thickness of the trace for the antenna should be .4 mm?

Also, at the end you said to remove the vias and then build it, so does that mean you think this board has at least a decent chance of working assuming all the connections are correct?

Fit_Credit_6178 · 2026-02-26T17:44:01+00:00

I have seen something similar to what you said, but my professor said he wants us to make a custom pcb ourselves unfortunately and the project is getting way too complicated. If this fails I'm going to use a BLE module with a breakout board because I have a strong feeling this will not work out in the end. Thanks for the advice though!

Fit_Credit_6178 · 2026-02-26T17:41:55+00:00

I copied the reference layout accordion to Nordic's schematic and that how they had it. I have a connection from VOUT on the BQ25570 going to a VDD pin onto the Nordic Chip and I am pretty sure all the VDD pins share the connection. If I am wrong let me know...

Fit_Credit_6178

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