Looking for a schematic review... - Page 1
Forum section: electronics / projects

author: TheStickman
author_rank: Newbie
timestamp: March 05, 2025, 01:09:11 am
content: Hello all,If this kind of post is not allowed, please remove.I've designed a replacement board for an electric fireplace/space heater unit. I've got the board assembled, and I'm in the process of testing and building the firmware with ESPHome. I do have a little issue, however. Every so often (time varies... sometimes when I first turn it on, other times after some hours), the MCU locks up and the LEDs turn on full bright. I'm not sure if it's a design issue or bad soldering on my part. (I did find a few bad solder joints).Anyone interested in looking at the schematic and providing some advice and mentoring? I would appreciate it!JD

author: Andy Chee
author_rank: Super Contributor
timestamp: March 05, 2025, 04:53:38 am
content: Quote from: TheStickman on March 05, 2025, 01:09:11 amPost a picture of the PCB board layout

author: TheStickman
author_rank: Newbie
timestamp: March 05, 2025, 09:55:55 am
content: Thanks for looking!

author: JJalling
author_rank: Unknown
timestamp: March 05, 2025, 01:41:47 pm
content: I guess it could be because of no flyback diode on the relay.Br Jonas

author: PGPG
author_rank: Frequent Contributor
timestamp: March 05, 2025, 02:40:34 pm
content: Quote from: TheStickman on March 05, 2025, 01:09:11 amI don't know what are the ESP32... needs for connecting externally blocking capacitors. As it looks that you connected one (C6) than may be you have read that it is needed.If C6 is intended to function as blocking capacitor it should be as close as possible connected between pins 2 (VDD) and 1 (GND).THT capacitor is worse as its legs (from PCB connection point to capacitance inside it) are longer than in SMD capacitor. Each mm adds some nH making capacitance blocking action worse.Additionally you positioned it "as far as possible" from ESP32...When IC switches its internal states it needs very short (ns range) current pulse and blocking capacitors supply it. But each inductance on the way makes that during that pulse voltage at VDD pin related to GND pin drops down and everything that is at ESP32... is exposed to this disturbance.I suppose there are blocking capacitors inside ESP32... so the problem is probably solved by them but what are the reason for C6. Such connected as it is it is practically no difference if this capacitor is assembled or not.If they call for adding external 100nF capacitor than I would expect SMD capacitor positioned such that its pads could be directly connected to ESP32... pads 1 and 2.

author: TheStickman
author_rank: Newbie
timestamp: March 05, 2025, 09:41:35 pm
content: Jonas,Thank you for your reply. Funny enough, I initially thought to include fly back diodes to protect the chip from the inductive current of the relay coils. I decided to not use them because the ULN2003A datasheet says the following:Code:The diodes connected between the output and COM pin is used to suppress the kick-back voltage from an inductive load that is excited when the NPN drivers are turned off (stop sinking) and the stored energy in the coils causes a reverse current to flow into the coil supply through the kick-back diode.Do you think additional diodes would be of use in this case?

author: TheStickman
author_rank: Newbie
timestamp: March 05, 2025, 09:45:42 pm
content: PGPG,Haha, you are right, that cap is pretty far away... I'll move it on the board layout to be closer to the module. I'll also consider using an SMD component, although I was trying to stay through-hole where I could. Do you think a capacitor directly soldered to the module at pins 1 and 2 would help at all?

author: PGPG
author_rank: Frequent Contributor
timestamp: March 06, 2025, 01:14:16 pm
content: Quote from: TheStickman on March 05, 2025, 09:45:42 pmIf there are blocking capacitors inside module then I think adding externally 100nF capacitors is not needed.So I think that in such case all situations:- C6 is where it is,- C6 is directly at 1,2 pads,- C6 is not assembled at allare the same.But I don't know internal module construction.

author: PGPG
author_rank: Frequent Contributor
timestamp: March 06, 2025, 01:22:22 pm
content: Quote from: TheStickman on March 05, 2025, 09:45:42 pmHand assembling SMD (0603 size and bigger) is even simpler than THT elements (you don't need to continuously revert PCB).In 1988 I was using 100% THT.In 1991 I was using IC THT at top and all resistors, small capacitors (nF not uF) at bottom.From 1995 I am using only SMD elements (except terminal blocks, electrolytic capacitors, ...).

author: oldrev
author_rank: Contributor
timestamp: March 09, 2025, 02:27:49 pm
content: It looks OK to me. But the TPS562201 might be too expensive for an ESP32 project. I also don't understand the purpose of U4. Is it for level shifting? Why not use the MOSFET or BJT that you've already used elsewhere?