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arianptc01 , 11-12-2018, 08:30 AM

Dear friends,
I have designed this PCB for my product.
it is supposed to drive 2 24Volt DC 5 Amp motors CC and CCW.
and 2 linear actuators.
as power supply concerns, I have used switching power 24 Volt 10 Amp and 5 volt 3 amp.
my problem is sometimes lets say 2-3 times out of 10 times my board just stop everything and did not do any thing and not get any command from controller.(we have a remote controll to send commands through USART)
one of the relays just switches and then MCU just freezs
program is fine because i test it on different board from other designer.
please help.

thank you in advance

robertferanec , 11-13-2018, 02:32 AM

- This can create a lot of noise and you may need to be careful about circuit & pcb layout

- That could be that the noise from the high power part of the circuit / PCB may be causing MCU to lock down.

Suggestions:
1. Schematic improvement: Be sure you have enough filtering included in your circuit (e.g. capacitors and inductors used for filtering)
2. PCB Placement improvement: You may want to place all the high power components in one part of your PCB, MCU and sensitive components in different part of the PCB. Be sure, that high power currents are not going to influence and flow under MCU and sensitive components
3. You may want to consider to use 4 Layer PCB (High power GND and power currents flowing through tracks of a 2 layer PCB can be making your circuit very noisy and unstable - you may want to use power planes instead, there is big difference between 2 layer and 4 layer PCB properties)

arianptc01 , 11-13-2018, 12:45 PM

Dear Robert,
Thank you for your prompt reply.
I have 50volt 2200uf cap and 104 cap(100nf) in my design but not any inductor. I just missed that. I'm thinking of 100uh.
One question: Do I suppose to separate my 5volt ground from 24 volt ground?

Arian

Paul van Avesaath , 11-19-2018, 02:08 AM

did you try and put in a reverse current diode over the relay? by switching the inductance of a coil can do strange stuff on your PCB.
also looking at your PCB, there are a lot of open ground planes, it is good practise to add grond via's from top plane to bottom plane were ever you can!

@robert, yes I would also suggest to go to 4 layers.

robertferanec , 11-19-2018, 02:46 AM

- That is very hard to say - it really depends on many factors (schematic, placement, layout, ...). But, yes, if you are not sure, you may start with isolating the high power circuit from the control circuit - for example, they may be both on the same PCB, just design them as "two PCBs" connected in one place. Be sure you can do some testing in the place where the boards are connected e.g. you can place there some filters etc.

PS: I am not sure if you control your system wirelessly or through a cable, but if through cable, be very careful how your system is grounded. For example I have seen many problems when using UART or RS232 through PC, connected to one main socket and talking to a board which was powered from different main socket. In this cases using laptop running from battery helped.

Paul van Avesaath , 11-19-2018, 03:34 AM

also try and keep stuff like this to a minimum, you can add keep out tracks from polygons to fill voids were you don't want them... now you have a lot of "antenna's "all over your board.. or close the loop with a via to an adjacent plane.. assuming this is either GND or power, this can have a big impact in how your design functions...

arianptc01 , 11-19-2018, 12:23 PM

thank you Paul,
we have that in place.