Swap mechanical relays for MOSFET's or ? - Page 1
Forum section: electronics / projects

author: cs2000
author_rank: Contributor
timestamp: July 02, 2019, 11:53:38 pm
content: Hi all,Ive been working on this circuit for a little while on and off. I already use the basic circuit with just the arduino programming changed for various other things, so i know the PCB itself is good.I would like, if possible to shrink this, at the moment its around 750mm wide which is wider than i would like ideally (i know i could rotate the arduino and move the voltage regulator to save space too). The two largest things are the two mechanical relays, i was wondering if i could swap these for something smaller, MOSFET's or something else?Im currently using Omron relays from Digikeyhttps://www.digikey.co.uk/product-detail/en/omron-electronics-inc-emc-div/G5LE-14-DC3/Z3326-ND/1815628The new purpose for the PCB will "use" the relay a lot more, so im also concerned about the relatively short lifespan with it being a mechanical switch.The coils on the mechanical relays are switched by the 3v output of the arduino pins, so whatever they're replaced with need to also be capable of this. However, it needs to deal with inputs of up to 15 volts. Obviously the 15v can never go anywhere near the arduino for fear of letting the magic smoke escape!It may be that for my purpose, relays are the best choice and il just have to deal with the size, but id be keen to shrink the board if possible!I apologise for the messyness of my schematic, neatness isnt a concern at the moment, im not at that design phase yet.Ive just never dealt with MOSFET's before, so if these can be used, or indeed anything else, i thought what better people to ask

author: sokoloff
author_rank: Super Contributor
timestamp: July 03, 2019, 12:05:16 am
content: I'm guessing it's closer to 75mm than 750mm.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: July 03, 2019, 03:18:29 am
content: Can Arduino feed 40-60 mA for the relay ? Need a transistorRelay in overall offering a full isolation, like switching a AC wall connected table lamp on\off , or reconnect something, without any worries that you fry you circuit. A mosfet need DC, it connected to the common ground, and it pass current.So what exactly you switching are matter ...as an option it can be thyristor or triac, possibly galvanically isolated by some optocouplerhttps://www.elprocus.com/types-of-thyristors-and-their-applications/I would lay a board at very last moment, when everything work on a prototype

author: cs2000
author_rank: Contributor
timestamp: July 03, 2019, 09:00:39 am
content: Quote from: sokoloff on July 03, 2019, 12:05:16 amDoh, yes that will teach me for trying to do this thing late at night!@GigaJoe, yep, as i said, ive been using this Arduino, diode and relay combination in this exact layout across several different boards (all doing a very similar thing) and it never has an issue driving the relays.Of course, i did initially do the entire schematic design, then did the layout, it was only then i realised that PCB would really be larger than id like. I have no strict size constraints, but it just seems large.

author: emece67
author_rank: Frequent Contributor
timestamp: July 03, 2019, 10:23:22 am
content: .

author: cs2000
author_rank: Contributor
timestamp: July 03, 2019, 10:56:54 am
content: Quote from: emece67 on July 03, 2019, 10:23:22 amThanks for the comments, the load is indeed DC. Il take a look at building something like that up, see what it does for PCB space