Hi all,
I am previously hired professional for PCB design. However, with time and a little bit of learning from past experiences, I decided to design myself this time.
I am attaching the PCB Schematic, for anyone's kind review and feedback. I have used screw terminals for every external connection as stated below.
VIN is a voltage input of 24V from a Meanwell brand SMPS
T1 and T2 are screw terminals connectors for K type thermocouple
LIM1 is used for a mechanical limit switch
LED1 and LED2 are two indicators
OUT1, OUT2 and OUT3 are three outputs to run solid-state relays
Buzz is used to run 5V Buzzer
U3 is used to read output from a pressure transducer 5V
U8 is used to read Inductive proximity sensor DC 6-36v
My area of concern is the output readings from the pressure transducer, whether the same would be stable or not. My previous version had fluctuating readings from the pressure transducer.
If you were to design it under free pcb software say from JLCPCB or PCBWAY, they have their own checks and balances dependant on your initial design parameters.
You might just look for the DRC (Design Rule Check) buttons in EsayEDA
I am not familiar with 7-segment numeric LED display, so I have not looked at that.
Mostly nit-picking.
NET: PS I cannot see a pull-up/-down resistor, that might be needed, depends on the Nano
LIM1 / R2 what is the purpose? Current limitation? I would probably at least put a pull-up/-down resistor in the schematic. Maybe leave it out of BOM to keep it unpopulated. So that it may be fixed if there is a need later.
SSR (solid state relay) OUTputs: What kind of relay are you driving? SSR Max Input Current? I would guess the Nano outputs are not enough to drive the SSR. Is this tested? Even if the max ratings are fine, you might have some inrush. I suggest adding a Darlington array, for instance ULN2003A.
U3 NET: INP (for pressure) I would probably add a smoothing capacitor, like 100nF, to GND, depends on the sensor really.
U8 (inductive proximity sensor) depends on the sensor, but it seems to me you will fry the LED in PC817X3
24V input protection (untested) but I would probably trying something like this:
Hi @wittrup
Thank you for your effort, and for sharing your inputs.
Schematic_Steamer_2025-03-17.pdf (100.3 KB)
This is my old schematic which worked just fine. I previously had 3 SSRs connected to the PCB, and the Arduino nano was able to handle the load just fine.
As per your suggestions, I have added a capacitor for U3 (Pressure transducer).
Even with the relatively moderate currents used by the Nano and multiplexed LED display, this may be a lot of power dissipation in the regulator (perhaps (24-5)*0.1 = 1.9W) to expect the M version (not particularly heat-sinkable) to deal with.
You have wrongly changed the configuration of that 10kΩ Resistor R2 in the limit switch circuit.
Previously it was a pullup to the 5V supply, now it is just in series with the input.
Your wiring of the inductive proximity sensor is incorrect.
You do not have a GND connection going to the sensor.
The LED in the opto-isolator needs to have a resistor in series with it to limit the current.
It is probably not even necessary to have an opto-isolator. The output of the inductive proximity sensor is likely to be an open collector NPN transistor.
This is not clear from the seller's website.
You need to do a test to find out whether it is.
If it is open collector then you can connect it's output directly to the Arduino input, with a pullup resistor to 5V.
Apart from what has already been mentioned, I'd have grounded the emitter of the optocoupler instead of the collector and used an external pullup resistor on the load pin of the MAX7219.
Added resisters in the opto-isolator circuit. The opto-isolator is necessary, I tried using a resister to read output from the proximity sensor. It didn't work for me.
I apologise if I didn't follow 100%, or made any mistakes. Can you guys please review it once again?
Your design looks well-structured! For stabilizing the pressure transducer readings, consider adding a low-pass filter or a decoupling capacitor to smooth out fluctuations.
My area of concern is the output readings from the pressure transducer, whether the same would be stable or not. My previous version had fluctuating readings from the pressure transducer.
So is there a problem or not?
If not then what kind of help are you looking for?
