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Example on the [forum](https://www.letscontrolit.com/forum/viewtopic.php?p=60959#p60959)
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ReStructuredText
345 lines
16 KiB
ReStructuredText
.. include:: ../Plugin/_plugin_substitutions_p00x.repl
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.. _P000_Relay_page:
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Relay
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=====
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|P000_typename|
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|P000_status|
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.. image:: P000_Relay_1.jpg
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Introduction
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------------
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The ESP8266 can't switch high currents or voltages and no AC at all. But it can switch a relay that can switch high load, isolating high
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voltage from the ESP circuit. There are several relay types in the wild.
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The ESP can control a relay using one of it's GPIO pins. All relay boards that work with Arduino should also work with the ESP module.
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Note this is only a possible application of the ESPs ability to send a logic 1/0 (TTL at 3.3V) on a GPIO. These relay are usually available
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as 1,2,4,8,16 Relay modules and work electromagnetically. They can switch both AC/DC(or imitate a button press of a remote for example)
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as they are "power operated mechanical switches". Each relay has the screw terminal. The middle one is usually "always connected" terminal.
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The NC contact will be connected to the middle terminal when the relay is not powered. The NO is connected when the relay is powered
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and activated. Note that there are "active high" and "active low" versions of these relays.
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There are mainly two relay types in the wild: The good old mechanical relay with the nice "click-clack" sound and the electronic relays, so called
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"Solid State Relays" (SSR) which are completely silent.
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Specifications:
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* Opto coupler (mechanical)
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* Solid state (SSR)
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Relays are the most used actuators in home automation. Most people use breakout boards with a relay on it. Sadly there is no "standard" relay board.
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It seems every small manufacturing garage in china has it's own layout and schematic. Some use 5V, some use 12V, some do with opto couplers, some without...
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the perfect chaos. Several problems result from this chaos. Relays keeping switched on no mater what your ESP says. Relays not switching at all.
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And last but not least - sometimes they work. Let's get some order into that chaos.
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.. note::
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You have just got your brand new relay board and it does not work. What to do?
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At first you should check the switching level. Is it switching on with "high" or with "low"?
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* Connect the board to power only (5V or 12V usually).
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* Plug a jumper cable to one of the inputs.
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* With the other end of the cable touch GND and +Vcc (5V or 12V).
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On one of these touches the relay should switch. If it switches when connecting to GND the board uses "low" as active (relay on) signal.
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In this case diodes or a transistor / FET as described above might help.
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Connect the board to the ESP carefully. Check voltages, the power supply should be able to deliver enough current for the relays!
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Check the connection cables. Jumper cables are well known for slack joints.
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Mechanical relay
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----------------
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The mechanical relay is a simple construction.
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It consist of a coil, one or more contacts and a spring. The spring keeps the contact in the "open" position. If the coil gets current, the magnetic
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field pulls the contact into the second position, the contact closes. As soon as the current is switched off the spring pulls the contact back.
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Mechanical relays may just have one contact switching to closed if the coil works (Normally open or NO). The contact might be a changeover contact which
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has a "common" connector and a NO (open without coil current, "normally open") and a NC (closed without coil current, "normally closed") connection.
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There might even be several contacts in one relay.
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There are several special types of mechanical relay
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Latching relay:
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.. image:: P000_Relay_2.jpg
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One current pulse switches on and keeps on when current goes off, a second pulse switches off.
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Polarized relay:
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.. image:: P000_Relay_3.jpg
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These relays have a defined + and - pin for the coil that must be followed.
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.. warning:: These micro relays can not switch mains voltage! Use them for low voltage door openers or similar.
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Pros and cons of mechanical relays
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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:green:`+` Several contacts in one relay available.
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:green:`+` NO/NC available.
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:green:`+` Limited resistance to overload and overvoltage.
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:red:`-` Noisy, might disturb in a living room or bedroom.
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:red:`-` Mechanical, moving parts that might wear out over time.
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:red:`-` Contact bumping when switching.
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:red:`-` High current for the coil, needs a transistor or FET for driving and generates peaks on power supply.
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:red:`-` The coil induces high voltage when switching off.
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Solid state relay
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-----------------
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The solid state relay, SSR for short, is a complex electronic circuit. It uses an opto coupler for input, this isolating the driving circuit from the load voltage.
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Isolation voltage is usually 2000V, 4000V or more. The switching element usually is a triac for AC switching types. For DC there are types with a MOSFET as switching element.
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There are several special types of SSR relay
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. image:: P000_Relay_4.jpg
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As with the mechanical relays there are specialized types of SSR's.
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**AC Type** : Can only (!!) switch AC. AC with zero crossing circuit. This type switches on and off if the AC voltage is at the zero point. **Expensive** and necessary only for special applications.
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**DC Type** : Can only (!!) switch DC! And a lot more that are reserved for special cases.
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Pros and cons of SSR relays
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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:green:`+` Completely noiseless
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:green:`+` Low driving current and voltage available. Some types can be driven directly from the ESP.
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:green:`+` No mechanical parts, no wearing out.
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:green:`+` No contact bumping.
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:green:`+` No voltage peaks on the low voltage side.
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:green:`+` Available for very high current for an affordable price.
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:red:`-` Very sensitive to overvoltage and overcurrent.
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:red:`-` No NC available usually.
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:red:`-` Usually with only one or sometimes three "normally open" circuits.
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:red:`-` Needs cooling! Smaller relays up to 5A must be mounted with at least 1cm distance to other parts.
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:red:`-` Bigger relays usually need a heat sink. Watch out: Heat sink may carry mains voltage with some types!
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:red:`-` Leak current! These relays leak some current even if switched off.
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Leak currents
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~~~~~~~~~~~~~
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Leak Current from SSR's might lead into problems under certain circumstances.
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The both types shown above ("Hoymk D3805KH" and "Mager GJ-6-L", 5A AC) were tested here.
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The Mager GJ-5-L showed a low leaking current and is useable for most purposes.
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The D3805HK showed a really high leaking current, enough for a 10W LED to glow and a small solenoid valve to keep open!
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This is not recommended for normal use.
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Meanwhile a third sample arrived: The SSR-D32A380/5 sold by Pollin.
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Similar to the D3805HK it shows a leaking current, as the test LED is slightly glowing in the dark when off.
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It seems to be a lower leaking then with the D3805HK, this is subject to some further investigation.
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The advantage of the Pollin SSR: It contains a small LED on the top indicating if the relay is on.
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This SSR is a bit bigger then the other two types tested, it just fits the case. So holes for the LEDs
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can be drilled on the top side of the case.
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.. danger::
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Always remember that a switched-off SSR is not completely switched off!
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Even a small leaking current is enough to give a shock. Nice surprise if you're on the ladder changing bulbs....
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Choosing your relay
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~~~~~~~~~~~~~~~~~~~
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Which relay should be used?
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Well, this depends on what you want to switch. If you control a heavy motor or pump, I'd always prefer a mechanical relay.
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The resistance against short overcurrent is a good point here.
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For experimenting we prefer mechanical relays too - we just love the "click" sound, i.e. we don't have to connect a load to see if it works.
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If noise counts or if you place the relay in a dusty or humid environment a SSR is the better choice. It's completely encapsulated so dust
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and humidity can't damage it. As it has no mechanical parts it is completely noise-free. So it's the perfect choice to switch lighting in a living room or sleeping room.
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Of course you have to chose a relay that fits your parameters.
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Which voltage you want to switch? AC or DC? Which current?
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If you want to use a SSR for high current you have to calculate the space for a heat sink and you have to use a vented case. All these parameters
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have to be figured into your project. It is also possible to use a small SSR to drive a really heavy external relay for a heavy machine for example.
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Wiring
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------
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.. code-block:: none
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ESP Relay (board)
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GPIO (X) <--> IN1
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GPIO (Y) <--> IN2
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Power
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5.0V <--> VCC
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GND <--> GND
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Setup
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-----
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No device is needed, generally you use rules to activate relays, or you send commands to activate them. Below you
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find more information on how to do this.
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.. note::
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If you want to monitor and have the GPIO state published you do this by adding as a |P001_typename| ,
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it will not be a switch per say but you will get the state published automatically.
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Rules examples
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--------------
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.. code-block:: none
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On Switch#State Do
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if %eventvalue1%=1
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GPIO,12,1
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else
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GPIO,12,0
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endif
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EndOn
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This rule will turn the relay ON when the button is pressed, and OFF when released.
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.. note::
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Events may be handled from an event queue, so by the time the event is being handled, the state of the switch can already be different.
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Therefore it is best to use the state of the switch at the time the event was generated,using ``%eventvalue1%`` .
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Indicators (recommended settings)
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---------------------------------
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No device is needed.
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Commands
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--------
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.. include:: P001_commands_GPIO.repl
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How to connect your relay
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-------------------------
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You can connect the relay in multiple ways, we explain them all below.
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Basic ESP circuit: mechanical relays
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The basic circuit is simple.
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As the relay usually consumes more current as the ESP can handle it needs a transistor or FET to drive the relay.
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To suppress the voltage peak when switching off the coil a free-wheeling diode is needed. This can be a standard silicium diode, a 1N4148 for example.
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.. image:: P000_Relay_5.jpg
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Well, there is another way to switch the relay. In the above example we used a NPN transistor or a N-channel FET. A PNP transistor or P-Channel FET can be used too.
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Some board manufacturers do this and now we run into problems promptly. The relays usually need some higher voltage then the ESP, 5V or 12 V in most cases.
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The PNP transistor in the example is connected to +5V. It will switch the relay to "on" if the voltage at the input is at least 0.7V below the Vcc of 5V.
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The ESP delivers a maximum of 3.3V if the GPIO is "high", around 0.5V if it is "low". Both voltages are far below the 5V-0.7V = 4.3V threshhold of the relay board.
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The relay is permanently on, no matter what your ESP says. We can get this to work in a simple way with a 5V relay board. A standard diode has a loss of around 0.7V.
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We can use this to get a higher output level from the ESP. We simply use two diodes in the connection between relay board and ESP. This raises the voltage from the
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ESP up to 3.3v + 1.4V = 4.7V. This is above the threshhold of 4.3V. If the board uses a FET it might be necessary to use three diodes. That usually will work.
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On top: This circuit switches the relay off if the GPIO is "high", this leading to irritations sometimes.
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The picture shows the basic circuit with a PNP transistor, and the " 2 Diodes " solution:
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.. image:: P000_Relay_6.jpg
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More complex: using an opto coupler
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Many widespread relay boards use opto couplers. Honestly we don't know the reason besides it looks good in advertising.
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In theory the opto coupler isolates the relay coil from the ESP circuit. Well, that's nice theory. In real world we use the same power supply for relays and ESP.
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This bridges the opto coupler as the circuits are connected via power supply making the opto coupler completely useless. Anyways the relay isolates the load from
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the ESP anyways. It might be useful only if relay switching interferes with the ESP. In this case you might try a separate power supply for relay coils.
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This isolates the ESP completely from the coil circuits. Note that a jumper has to be set for that on some boards.
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Again there are two possible ways to use this circuit. The opto coupler input has one pin to the ESP and one to ground - this works without any problem but it is not widespread.
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.. image:: P000_Relay_7.jpg
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Most boards we've seen connect the opto coupler to 5V or 12V and the other input pin to the ESP.
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.. image:: P000_Relay_8.jpg
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This runs into same issues as with the PNP transistor above. The high voltage of 3.3V from ESP is far below 5V, this keeping the relay permanently active.
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The solution is same as with the transistor board above. Use some diodes between ESP and relay board usually does the job with relay boards using 5V.
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Depending on the circuit you will have to experiment how many diodes are necessary.
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Boards with 12V
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~~~~~~~~~~~~~~~
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If your relay board uses 12V and needs "Low" to switch the relay on it gets somewhat more complex. Basically it is possible to use a lot of diodes but
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it's not very handy. You may try a Zener diode of around 8.5.. 8.7 V. Honestly we don't recommend it. In this case it is better to use an additional
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transistor or FET to get it to work. This has one advantage: It inverts the switching signal so a "low" output says the relay is off.
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.. image:: P000_Relay_9.jpg
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Special designed boards
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~~~~~~~~~~~~~~~~~~~~~~~
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There are some boards in the wild which can be configured if "low" or "high" should switch the relay on.
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With this boards you will have to experiment a bit with your ESP and the board, there should be a combination that works.
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.. image:: P000_Relay_10.jpg
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Note the jumpers down left - that's the configuration for switching on high or low level.
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Basic ESP circuit: SSR
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~~~~~~~~~~~~~~~~~~~~~~
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This is more simple. If you got a SSR that has an input of "3...12V" or "3...30V" it usually can be driven directly from the ESP.
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The only thing you should keep in mind: Do not omit the varistor (RVx in the schematics). It protects the SSR from voltage peaks that
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may kill it within some milliseconds. Instead of the varistor a TVS diode can be used, for example a P6K400CA.
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Be careful, you have to use a bidirectional type!
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.. image:: P000_Relay_11.jpg
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It is possible to direct drive a SSR from the ESP but we won't recommend this. We prefer the same circuit as with the mechanical relay.
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It makes the relay circuit more universal and reduces load on the ESP.
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.. image:: P000_Relay_12.jpg
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Instead of the 2N2222/BC547 you may use a small FET, a BSS138 or 2N7000 / 7002. Omit the 22K resistor if useing a FET.
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R2 is needed if your relay can't take the Vcc directly. If you use a "3...30V" input SSR it's not necessary.
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Any opto coupler is completely needless if you use a SSR. The SSR has an opto coupler built in to isolate the load from the ESP.
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At this time there are not that much relay boards with SSR in the market, this will change over time as they get more popular.
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From what is on the market be careful what you buy. Most boards we've seen nowadays on AliExpress and Ebay have a DC relay installed - they can switch DC only! They can't switch mains voltage.
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Some words about DIY relay boards
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---------------------------------
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All in all it's no problem to build your own relay board fitting your needs exactly. But watch out if you want to switch
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mains voltage. There is a reason why in some countries the policies specify a minimum distance between the parts with high
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voltage and the low voltage circuits. Do not use experimental PCB's with copper pads or stripes!
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Good breakout boards are milled out, there is a gap in the PCB for isolating mains from low voltage.
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Prefer these boards over others without milling.
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.. danger::
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Be very careful - mains voltage can burn your home or kill you. In case of doubt ask an expert!
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Where to buy
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------------
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.. csv-table::
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:header: "Store", "Link"
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:widths: 5, 40
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"AliExpress","`Link 1 ($) <http://s.click.aliexpress.com/e/cM59HXVq>`_ `Link 2 ($) <http://s.click.aliexpress.com/e/cerop6s0>`_"
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|affiliate|
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.. More pictures
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.. -------------
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