Today I received my dual relay board from Electrodragon. The device is a fair bit bigger than the ITEAD Sonoff I had some fun with earlier this week, but instead of only one relay switched output, the Electrodragon got two… Or does it?
What we got
The dual relay board from Electrodragon, is made to have two outputs, but it should be obvious to anyone that both outputs can not be used as it is, because of the obvious design flaw in the case.
I am not sure how anyone would think it would not be noticed, or even how anyone would think this is remotely close enough to actually be used. It is close to impossible to get a wire into the terminal furthest to the left, and even if you manage to get some of the wire into it, you will be defeated by the case not allowing your screwdriver to reach the screw to clamp down on the wire. Right now I dont have an idea about how to use the second output, and at the same time route and secure the wires properly, but we will see…
Next thing I did, was to clip the top of the case, and to make things a bit more complicated, some parts of the top part of the case, is being supported right in front of the terminal.
Something more to consider… hmm, I need a few days to think this through properly…
After turning the case around multiple times, to get an idea about what to do with the wires to get them out properly, I took the pcb out, and had another surprise.
Can you spot it?
Yup, looks like someone forgot to solder the mains input terminal.
After soldering it on, I decided to replace the firmware, which didn’t require much research.
On the bottom of the PCB the silk screen tells what the different pins are for, only thing I would like it to include too, is which one GPIO00 is, to enable flashing new code, turns out BTN1 is connected to GPIO00, and holding the button down puts it into flash mode.
After that it is only a question about connecting RX from the adapter to TX on the electrodragon, and opposite for TX from the adapter to RX on the electrodragon.
The relays are connected to GPIO12 and GPIO13. On the PCB there is a 1×4 row of pin headers, these are for connecting a DHT temperature and humidity sensor, the datapin here is connected to GPIO14.
The visual design of the case is decent. Without a sticker on, it looks like it is just some random generic case, but that can have its advantages too, as it more easy lets you turn it into something more of your own.
When looking at the practical design, I can’t give it many points, as it got a pretty bad design flaw, which makes it impossible to use all the functions it is announced to have. However, one of the good things, is the dark end-caps. When the wire is going through the opening under them, they got small teeth, which will grip the wire and will act as strain relief, while also holding the entire case firmly together.
When looking at the PCB, it seems pretty decent. It use a little 5V 700mA switching power supply module to drive the relays, with a 1117 regulator for the 3v3 going to the ESP8266.
Having a closer look, I see a lot of things I spend so much time to avoid when designing my own PCBs… And that is proper ground-pour. I just don’t like it when it isn’t covering properly, when some design changes would make it look properly.
One of the places is where. It is all low voltage, and by moving the traces a bit, the ground pour would have filled it all nicely.
Around the mains voltage, the ground pour have been entirely removed, which is a fine way of getting higher isolation. At the bottom of the page one of the low voltage traces is pretty close to one of the pins on one of the relays. However, the pin is for the coil in the relay, so it should still be fine.
A thing I find concerning, is the traces carrying the mains current from one side of the board, to the relays at the opposite side.
The only thing they list on the product page, is the relays specifications, which is 125VAC 10A, 250VAC 10A, 10A 30VDC, 10A 28VDC. Based on this, they suggest it is possible to pull 2x 10A at 230V~? It sums up to a whopping 4600W, through these thin traces? I would not go anywhere near that, not even half of it.
The dual relay board from Electrodragon is a nice little device, especially for the price. While typing this, the price is $6 plus $2.80 for shipping. However, there are some design problems where the only conclusion I can come to, is that they could not be bothered doing it properly. This is both to the ground pour on the pcb not filling out properly, but mostly the case not matching the terminals on the PCB properly.
Last is the ratings, or more lack of. On the product page I don’t see any clear indication of how much current the relays and PCB can handle, only how much the relays can, which is most likely a lot more than the trace going to them actually can handle without starting to glow.
The ground pour not getting enough attention, is something I could easily live with, I just need to take some deep breaths and try to keep my OCD from remembering it all the time. But the case not allowing for both outputs to be used, and the lack of clear power rating, is something making me rethink what to use this for, or if I should use it at all, because it makes me feel ike they didn’t really care when it was designed.