PCB Design

[ranum]

Not sure if this is the right place to post. This is my first pcb design for metal detector.
Please flame on it. Apologies on the poor copper pour.

[tszaboo]

Maybe you should post something to flame on.

[ranum]

Was on mobile before. I've updated it

[xvr]

Very strange PCB. Do you really have only one side PCB? There are a lot of unconnected capacitors and pair of shot circuited.

[pcprogrammer]

Maybe an idea to post the schematic too.

But indeed I have to agree with xvr that the PCB looks strange. Components seem to be connected to the top copper fills having them shorted, then the two traces coming from the big connectors making a weird dance pattern with the passage on the other layer.

Why the Arduino nano and only have two connections from it to the bigger adapter board.

I would say, lots to flame on.

[ranum]

Not sure what you meant by that.  I have attached more, maybe that helps

[ranum]

I have updated the post with new images.  Nano was for wifi connectiivity, those two and UART RX TX. Have to agree I have hard time with placing components

[pcprogrammer]

Not sure what you meant by that.  I have attached more, maybe that helps

I meant the traces seen in the attached picture.

You mention the nano for wifi connection (of which I was not aware that there is a nano with wifi), but would it then not be simpler to just used an ESP32 module for the whole project? Or has the other board a much more powerful processor?

The schematics don't include the two daughter boards.

[mariush]

Are you actually using the 12v for anything? 

You could just use 4 AA batteries to get up to 6v (for non-rechargeable alkaline) or ~4.4...5.2v (if using rechargeable batteries) and just use a 5v regulator with very low dropout voltage  or a buck-boost 5v regulator

For example AP2202K :   https://www.digikey.com/en/products/detail/diodes-incorporated/AP2202K-ADJTRG1/4470808

It's adjustable, accepts up to 13.2v input, outputs up to 150mA, and a maximum dropout voltage of 0.35v at 150mA  (0.15v at 50mA)  - even with 4 rechargeable AA batteries, you'll have around 4.5v on output which should be good enough, your microcontroller will work just fine even with less.

AP2210K - https://www.digikey.com/en/products/detail/diodes-incorporated/AP2210K-ADJTRG1/4470821  - goes to 300mA, maximum dropout voltage is higher, but at low output currents it will be about the same as previous regulator

Alternatively, you could use a couple 18650 lithium cells in series and a charger that can charge them ... this way you're guaranteed to have more than 5v on input and long battery life.

for example MP2672A - https://www.digikey.com/en/products/detail/monolithic-power-systems-inc/mp2672agd-0000-z/13572801  - can take in 5v from a USB port, boost it up to 8.4v and charge the cells, and also supply this voltage while charging the batteries on a "system out" pin, and when the 5v is disconnected, the battery is connected automatically to system out pin, so you can put your 5v regulator on that pin


for your negative voltages you could use a charge pump in inverting configuration, like LM2776 for max 200mA - https://www.digikey.com/en/products/detail/texas-instruments/LM2776DBVR/5356685 -  or LM2660 if 100mA is enough https://www.digikey.com/en/products/detail/texas-instruments/LM2660MX-NOPB/366876   or TPS60403 if 60mA is enough : https://www.digikey.com/en/products/detail/texas-instruments/TPS60403DBVR/1672064

 

[ranum]

12V is the convenience option for wall plugs. Currently using +-5V, according to the coil impedance.  This also give option to change LDO output with resistor if needed. I should note that this is a fixed metal detector for school project instead of handheld.

Other than that, I have being bench PSU and its drawing 0.5A at 1kHz on both rails. Current sensing reading was a lot more than what was shown on the bench PSU, but was in fact internally limited to audio amp.

Audio amp is limited to 3A, LDO 1.5A while this may never reached, I just design it for the sake of technical limits.

[ranum]

One can say it was a decision that was too late to change. Anyway the STM is higher performance, and the easiest say to deploy this is to add wifi board.

I understood what you meant, it was poor layout. I try change pin to the same side/ do proper layout