Freelancer.com has job categories for all sorts of stuff, including most flavours of tech, including electronics design. Freelancer.com also own/absorbed several of their once-were-competition websites too now. You can sign up as an employer, freelancer, or both.
I used it a couple of years ago to get my head back into my old career (EE) after a decade's+ absence. I did it without the expectation of making any *reasonable* amount of money from it, and that was certainly the case - for me, an Australian, I was competing with people whose cost-of-living was a small fraction of mine, so they bidded proportionally lower, thus win most of the jobs. I would *hate* to have to make a living from Freelancer.com if I were living in any relatively affluent/developed nation. But I carefully chose a few projects where there was an inkling I could play to my strengths, impress the client, and indeed I've carried 2 of those clients out of Freelancer.com & into reasonable 'first world' rates as they value my input & we continue to develop their prototypes into products. Things also get better there once you complete a bunch of projects & get a decent reputation (which is visible to all on your profile).
Just bear in mind that Freelancer.com are utter control freaks, your ability to communicate with employers is very limited, with other freelancers is virtually impossible, and they nickel-and-dime you for every little transaction, mostly paid by the freelancer, but also the employer too. For example, Freelancer.com's X% cut (X depends on what level of membership you subscribe to) when you're the winning bidder comes out of your balance/bank-account AT THE TIME YOU'RE AWARDED THE JOB, and they keep it whether or not the job is completed or a success, unless you put up an almighty shitfight. Frankly I don't have much respect for their overall M.O. in this sense, you always come away with the sense that Freelancer.com looks after Freelancer.com first no matter what and that you're just a piece of meat, and I was glad to put them behind me after 6-9 months. BUT, it served its purpose for me.
Good luck!