GPIO0 needs to be grounded during power up or reset to go into program mode. Once the chip boots GPIO0 can be high.
Jumper works unpower it put jumper on power up pull the jumper and your ready
groundFungus:
GPIO0 needs to be grounded during power up or reset to go into program mode. Once the chip boots, GPIO0 can be high.
Thanks a lot for the reply. I'll use a push button instead. A jumper might be too small to remove if the components are crammed into a small PCB.
be80be:
Jumper works unpower it put jumper on power up pull the jumper and you're ready
Thanks for the reply. Should I consider removing/changing the value of the 470Ω resistor?? Pieter said that connecting GPIO0 to GND directly wasn't good practice.
It all depends on how robust you want it to be.
The danger of connecting GPIO0 directly to ground is that you short out the output if you set it as an output in your program and drive it high. If you are the only person writing code and uploading it, you probably don't need the extra resistor.
Same goes for reset. You could use it without a reset button, and just power cycle it instead. But this makes programming a whole lot more cumbersome. If you plan on ordering thousands of these boards, and you only plan to program them once, it might be a sensible choice to leave them out, but if you're just going to order 10 of these boards to experiment yourself, it'll be much easier to just add it, and the cost difference is negligible.
Pieter
be80be:
The drive circuitry in electromechanical relays is galvanically isolated from the relay contacts, and the contacts themselves are also isolated from one another. This isolation makes electromechanical relays an excellent choice for situations where galvanic isolation is required.Now where do people keep getting the need for a opto-isolator Just asking cause in 40 years I never seen one that put line voltage on the low side.
I've fixed a bunch that was wired wrong but that's a whole new bag of worms.
It's true that in normal conditions, the relay coil is isolated from the switch contacts, however ...
Take a look at a typical relay:
The white wire carries all current flowing through the switch. If the current is too high (output is shorted, device being switched blows up, etc.) or if there's a voltage spike (e.g. lightning strike), the isolation will just go up in smoke, and it's not unlikely that the wire touches the coil (either by touching the wire on the left, or by melting through the coil's isolation). If the coil is connected to the logic directly, you end up with lethal voltages in your "low-voltage" circuit. This part of the circuit is often grounded, or has connections to other devices. If you have the USB cable plugged in to your brand new $2000 computer while this happens, you're going to hate yourself for not spending the extra dollar or two on a few opto-couplers and a separate power supply.
Pieter
I think you missed something there the coil is insulated from the core the contacts are insulated.
And even cheap ones are rated for over 1500 volt galvanic isolation
The relay you popped open looks like a auto relay. The white wire is rated for the rating of the relay so if that's 10 amps and you build for that it's going to be good.
I've seen opto-couplers burn off the board and do just as much damage or more.
And my point is it's not a fact when people say a relay is not galvanic isolated
Because they are some even better then the rest for AC i use the ones with the AC lugs on top.
But now if you add a opto-coupler it's not going to hurt anything it just add a extra safety factor.
I'm all for extra safety, but every safety step you add may also add an extra potential point of failure.
Reading the discussion here I'm more and more wondering how much safety it adds (an extra layer of electric isolation) for how much cost in reduced reliability (extra components).
In 40 years this is what I've seen. I've seen felled PLC with parts of the copper burnt off the PCB that you couldn't tell what the opto-coupler was.
Then I've seen relay with the top burnt off because of wiring wrong that I then fixed with a new one and they work like new.
I've seen poorly made solder joints that was fixable.
And yes I've seen some take out the low voltage side but guess what that was because someone put line voltage on the low voltage side. I'm not saying it can't happen but it's still a fact that the relays you see on these relay boards are isolated.
Those little 5 volt jobs with 250 volt @ 5 to 10 amps have good isolation for there rating.
You still need away to use them be it opto-coupler or transistor mosfet is up to you.
Many online guides recommend using opto-couplers (e.g. https://www.allaboutcircuits.com/projects/use-relays-to-control-high-voltage-circuitswwith-an-arduino/), and 90% of the Arduino-compatible relay modules are optically isolated.
I've always thought that the two main reasons were 1. extra isolation from the high-voltage side, 2. isolation between the microcontroller and the noisy coils of the relays.
I'd love to be corrected by someone who can explain the real reason why opto-couplers are so often used for driving relays.
Pieter
At a hobby level there used in everything. But I can name 6 things in every ones house that I fix none of them use them.
but my point is and the quote I posted about
he drive circuitry in electromechanical relays is galvanically isolated from the relay contacts, and the contacts themselves are also isolated from one another. This isolation makes electromechanical relays an excellent choice for situations where galvanic isolation is required.
Is from one of the most used relays in home appliances.