I think I just found the most dangerous thing ever - Page 1
Forum section: electronics / general

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:03:42 pm
content: I can count at least 10 design faults and ways to kill yourself with this all for a generous £5.89...sigh...The thing is I was referred to this by a "maker" friend who said it was cool he could control his 240v desk lamp with this plugged into his laptop. Instant lecture...sigh...Edit: I've just been told "I've wrapped Kapton around it - it will be fine". Better take the black suit to the dry cleaners.

author: Monkeh
author_rank: Super Contributor
timestamp: February 26, 2016, 04:07:59 pm
content: Just allow natural selection to do its thing.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:10:56 pm
content: Quote from: Monkeh on February 26, 2016, 04:07:59 pmI appear to not have a choice anyway.

author: JoeN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:21:58 pm
content: Any idea if that IC is an isolator or not? I see the 10 other problems, but I just wonder if they at least did that part right.Now that I look at it, I guess probably not. Looks like one of the many FTDI clones out there. (I now see it is a CH340 which is a low cost one hung low USB to serial IC which I have used and they work quite well). Surprised it has enough drive for the relay.I spy another IC on the underside. Perhaps this is the driver and maybe an isolator as well? Or an isolator and that transistor as the driver? Not that it is done correctly without the slots and some sort of enclosure anyway. Hey, you can always touch those terminals to see if the AC is on or not.If they marketed it as something to switch low-voltage DC for DC applications like running LEDs or whatever I guess that would be OK. AC is not OK with this.

author: djQUAN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:32:44 pm
content: Nope, definitely not an opto. An SOT23 part is probably a transistor driving the relay.The lack of creepage and clearance distance scares me. Not to mention a whole ground pour even around the high current contacts.You'd have to wonder how wide are the traces for the relay contacts laid out on the top side.

author: JoeN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:38:40 pm
content: Quote from: djQUAN on February 26, 2016, 04:32:44 pmWhat do you suppose that bottom IC is? There are isolators that come in SO-8 packages (e.g.http://www.digikey.com/product-detail/en/HCPL0638/HCPL0638-ND/1647310- top quality but I assume there are one hung low versions for 30 cents each as well) Not all of them are the chunky ones. The CH430 does not need a memory.

author: AF6LJ
author_rank: Unknown
timestamp: February 26, 2016, 04:39:34 pm
content: This is scary...

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:41:14 pm
content: I didn't even see a picture of the bottom of it. Ouch!Not a CH340. Too many pins.

author: djQUAN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:42:41 pm
content: Quote from: JoeN on February 26, 2016, 04:38:40 pmEven if it was an opto isolator, you'd need an isolated voltage to supply power to the output side and the relay coil. There isn't a sign of an isolated supply on the other side. Relay coil is also 5V so it is definitely powered off of USB.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:46:06 pm
content: Another picture of the bottom so you can see the crappy soldering and filed off IC identification...

author: djQUAN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:50:10 pm
content: Quote from: MrSlack on February 26, 2016, 04:46:06 pmI was looking for another clearer pic and I also stumbled upon similar to that one(http://www.gearbest.com/development-boards/pp_63975.html)It is a little better designed as there are isolation slots and no ground pour on the contact side. But it is still dangerous if you inadvertently touch it while live. Could be a little safer if it was at the back of the PC out of reach?

author: JoeN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:51:13 pm
content: Quote from: MrSlack on February 26, 2016, 04:41:14 pmI took the image the OP provided and searched for it on Google Images to find the auction. I didn't want to post this before but I assume everyone here knows the risks:http://www.ebay.com/itm/LCUS-1-USB-Intelligent-Control-Switch-USB-Relay-Module-CH340-/321900033197The guy says CH340. I took him at his word because I know how cheap these parts are, it's exactly what they might use. I didn't count out the pins. Still haven't. I guess I don't care all that much. It must be a very inexpensive USB/UART bridge IC.

author: JoeN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 04:56:41 pm
content: You could give your friend something like this and have him take that thing and put it in a grounded project box:http://www.ebay.com/itm/NEW-USB-Isolator-1500v-isolator-ADUM4160-USB-to-USB-/201490541160

author: nctnico
author_rank: Super Contributor
timestamp: February 26, 2016, 04:59:12 pm
content: These kind of circuits bring back memories! Somewhere in the late 80's I was at a large (home) computer exhibition / market to show some software I had written for a programming contest. The kid next to me build some light controller boards so he could control a couple of 220V lamps from his Commodore 64. He never heard about isolation either so when two boards touched his Commodore 64 got fried. No problem he explained and went off to find a donor Commodore 64 and he was up & running within the hour.

author: StuUK
author_rank: Frequent Contributor
timestamp: February 26, 2016, 05:01:16 pm
content: Quote from: Monkeh on February 26, 2016, 04:07:59 pmChuckle!!!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 26, 2016, 05:34:48 pm
content: Why would you need an isolator - the relay is the isolator!

author: mtdoc
author_rank: Super Contributor
timestamp: February 26, 2016, 06:03:38 pm
content: Quote from: mikeselectricstuff on February 26, 2016, 05:34:48 pmI'm glad you asked that since I was thinking the same thing though was afraid to ask since I have very little design experience.Also it would be helpful for beginners like me if each of the design flaws was spelled out.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: February 26, 2016, 06:18:16 pm
content: the whole thing is an overkill, why and FTDI or any usb to serial for just switching a relay on and off. i thing any basic MCU with built-in usb could do that, either in HID mode or VCP.Quote from: mikeselectricstuff on February 26, 2016, 05:34:48 pm+1and it's kind of ... meaningless to use an USB just to control a signal output ! what possible application for that !!

author: Seekonk
author_rank: Super Contributor
timestamp: February 26, 2016, 06:48:20 pm
content: No one worried about me growing up! In fact I have never heard of anyone being electrocuted by a hobby, just the odd lineman falling into wires. I think you are more likely to be eaten by a shark.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 26, 2016, 06:53:21 pm
content: Quote from: hamdi.tn on February 26, 2016, 06:18:16 pmBut you don't need any firmware - just use a handshake line.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 26, 2016, 06:54:14 pm
content: Quote from: Seekonk on February 26, 2016, 06:48:20 pmFamous last words.I had a friend who is a couple of fingers short after as a kid suggesting that no one got hurt playing with fireworks.

author: Brumby
author_rank: Unknown
timestamp: February 26, 2016, 09:53:11 pm
content: Quote from: mikeselectricstuff on February 26, 2016, 05:34:48 pmI can see the fixed USB plug being problematic in certain situations and the exposed AC connections would need something covering them, but I was thinking the same thing..... or is there something I am missing?

author: German_EE
author_rank: Super Contributor
timestamp: February 26, 2016, 10:04:52 pm
content: There is a copper pour over most of the bottom PCB surface so the clearance between PCB ground and the AC contacts will be about 1mm. Plus those exposed mains connections

author: Brumby
author_rank: Unknown
timestamp: February 26, 2016, 10:05:47 pm
content: OK - THAT is a problem!

author: Psi
author_rank: Super Contributor
timestamp: February 26, 2016, 10:06:07 pm
content: They're two different PCBs / versions.The first is quite dangerous if used on high energy circuits,The 2nd is much better, it has an isolation slot and no signal-side copper near the relay contacts.The more serious issue with both of them for 110/230v is the urge to pull them out of your laptop like a USB key and grip the exposed relay pins on the bottom side of the pcb.

author: Brumby
author_rank: Unknown
timestamp: February 26, 2016, 10:08:42 pm
content: Yes - I noticed that now (and was just about to post that very observation).My comment was on the second board (easier to see clearly).

author: H.O
author_rank: Frequent Contributor
timestamp: February 26, 2016, 10:21:21 pm
content: Playing a bit of devils advocate here....I'm not saying the design is that great by any means (the one with the isolation slot and no groundplane seems better though) but where exactly does it say it's meant to, or designed for, switching mains voltages?OK, it doens't specifically say it's NOT meant for that or what else it's not meant for, unlike the vacuum cleaner I bought recently...They do say the relay is rated for 250VAC so I guess you could say they're implying it can be used for mains but really, people not knowing better simply doesn't know better. If I buy two ofthese 230V Schuko plugsand put them at either end of a cable "they" become pretty freakin' dangerous. They weren't designed to for that but nowhere in the listing does it say I should not do it...

author: JoeN
author_rank: Frequent Contributor
timestamp: February 26, 2016, 11:16:30 pm
content: So what is the 8 pin IC on the bottom?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 26, 2016, 11:44:55 pm
content: Quote from: JoeN on February 26, 2016, 11:16:30 pmeeprom for USB config?

author: nctnico
author_rank: Super Contributor
timestamp: February 26, 2016, 11:56:31 pm
content: Quote from: H.O on February 26, 2016, 10:21:21 pmWhen there are relays people will connect 230V mains to them regardless the relais can handle it or not. Because of that I keep a 2mm minimum and preferably 4mm clearance between traces connected to relay contacts and the rest of the circuit in my designs.

author: JoeN
author_rank: Frequent Contributor
timestamp: February 27, 2016, 01:20:17 am
content: Quote from: mikeselectricstuff on February 26, 2016, 11:44:55 pmBoy, I wonder if I should get one just to find out. Is that common? Most of the cheap ICs I have seen don't need one.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 27, 2016, 10:29:43 am
content: I've bought one from aliexpress. I'll post back here when it arrives.

author: VK3DRB
author_rank: Super Contributor
timestamp: February 27, 2016, 12:04:33 pm
content: Quote from: JoeN on February 26, 2016, 04:21:58 pmIn some countries, life is cheap. Even so, the onlycreepageis the clown who designed it. As forclearance, there is plenty of that between his ears.This USB device is not dangerous so much, but will give the victim a nasty shock of a different kind...http://www.theregister.co.uk/2015/10/14/sneaky_220v_usb_fries_laptops/

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 27, 2016, 12:34:09 pm
content: Quote from: VK3DRBI rather like that. We put hot snot in all the USB ports in the office and lock the PCs in cabinets so people don't have access to the ports and cables. Also contractually, if you try and circumvent this, even if your iPhone has died before lunch time and you can't get your candy crush fix, you're fired on the spot. Stops this attack dead!

author: dannyf
author_rank: Super Contributor
timestamp: February 27, 2016, 12:35:51 pm
content: "The thing is I was referred to this by a "maker" friend who said it was cool he could control his 240v desk lamp with this plugged into his laptop. Instant lecture...sigh..."Seems to me you did indeed find the most dangerous thing, except that it is not what you think it is.It isStupidity.But that's how we as a spieces advance, according to Darwin.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 27, 2016, 12:43:20 pm
content: Unfortunately advances in medical science have made this somewhat less effective at removing some people...

author: Stonent
author_rank: Super Contributor
timestamp: February 28, 2016, 07:32:17 am
content: Quote from: mikeselectricstuff on February 26, 2016, 05:34:48 pm

author: SeanB
author_rank: Super Contributor
timestamp: February 28, 2016, 08:48:57 am
content: In the old days they would merrily mix mains power with signals in rack mounted equipment, especially in industrial controls where you typically use a 24VAC supply, but every so often you get a mains connection going in in the same colour cabling on the board. Can be a jolt to find 220VAC on a contactor, when the one next to it, identical in all respects aside from a small label saying 24VAC, is fine. One German manufacturer solved this by including in the machine an isolation transformer, with both a 24VAC secondary and a 220VAC secondary, with the primary being selectable between 115, 230, 277 and 400VAC via taps. That way you only get a large tingle, not a death blow. They also used DIAZED fuses, which is great but not so good when you look at the price of the replacement fuses. I replaced with a mix of DIN rail breakers instead, which have a big advantage on a 3 phase motor of disconnecting all 3 phases instead of leaving the motor to run missing a phase and burning out.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 28, 2016, 08:58:00 am
content: Quote from: Stonent on February 28, 2016, 07:32:17 amYeah,I couldn't see why everybody was getting their knickers in a twist about that.Mains rated relays operated by very much lower voltage supplies,(even "floating" ones),have been mainstreamElectronics for a Century or so.Such relays are built to specifications much stricter than most SMPS & the like.OK,there is a problem with the PCB version that does not remove the copper around the 240v terminals,but there is nothing wrong with the basic concept,if it is packaged safely.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 28, 2016, 09:19:04 am
content: The idea is fine, just this implementation is bloody awful.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 28, 2016, 01:30:18 pm
content: Quote from: MrSlack on February 28, 2016, 09:19:04 amI was thinking of it being intended for mounting inside an insulated enclosure,with all the 240v circuitry in that.To do that,though,the module would require a "B" receptacle,not an "A" connector.It apparentlyismeant to be hung on the end of a cable-----so itiscrappy!

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 28, 2016, 02:46:09 pm
content: There's a video of some Brazilians doing 240v breakdancing somewhere after some dodgy cabling. I suspect it's designed for the same audience.

author: Kilrah
author_rank: Unknown
timestamp: February 28, 2016, 03:33:21 pm
content: Quote from: vk6zgo on February 28, 2016, 08:58:00 amWhich the used USB connector doesn't encourage, OP's friend like most others when seeing this will say "cool, I can just plug it in my laptop" - with mains voltage 5cm away and live pins just laying on the table below.With an enclosure, proper USB receptacle and matching cable then yes...