The output pins of the hardware used by RemoteSign ESP devices can only supply a minimal amount of positive 3.3V current: 12mA max! There is only enough power to drive one LED per pin. All is not lost however as there are devices that can take the 3.3 Volt output to switch much bigger loads. Here are the types that can be used:
- Relay
- Transistor
- MOSFET
A relay is suitable for something that just needs to be switched on or off as needed. If one was to use a relay to switch a light on or off, it would work fine, but you would not be able to set the light to half brightness. This is because dimming is usually done by rapidly switching a light on and off and varying how long the on period is compared to the off period. Relays can't be switched on and off fast enough as they have a mechanical component, so a relay is not suitable if you want fancy lighting effects.
Transistors lose some of the switching current and also can't be switched as fast as a MOSFET.
MOSFETs (Metal–Oxide–Semiconductor Field-Effect Transistor) are very efficient, being able to switch high current loads with a very small voltage, and they can do this very fast. This makes them ideal for altering the brightness of LED lights.
MOSFET modules are also readily available, and can easily be connected up to a RemoteSign as follows:
Note, the diagrams here represent the RemoteSign ESP in the form of a WEMOS D1 mini. The connections for NodeMCU ESP8266 use the pins with the same labels.
Important: There are two types of MOSFETs, N-channel and P-channel. N-channel MOSFETs are switched using a positive voltage, and the ESP device pins produce positive outputs, so you must use N-type MOSFETs unless you have inverted the pin output and use the pin to switch the 3V3 power to ground.
N-channel MOSFETs switch the negative (ground side) of the circuit you are switching.
This can all be seen in the connection diagram above. You provide power to the RemoteSign ESP either with 5V to the 5V pin or with 3.3V to the 3V3 pin or via a USB connector. A 5V connection is shown.
Then, the pin that is producing the output is connected to the trigger connection on the MOSFET module. Complete the circuit by connecting the GND pin to ground of the ESP.
In the example shown, when pin D1 goes on, it applies +3.3V to the J1 pin. That causes the MOSFET to allow current to conduct between the in and out terminals. When the pin goes off, the MOSFET will no longer allow current to flow.
RemoteSign commands such as {LM}, {LC} and {SIG} set the output pins to switch on and off rapidly to produce varying brightness. MOSFET modules can be thought of as amplifying that output so that a heavy current devices will be switched an and off at the same rate.
A example of the load could be a 12V strip of white LED lights drawing 2 Amps.
To control a color light LED strip, you would define a color light channel that uses three output pins and those pins would drive three separate MOSFETs for the red, green and blue circuits of the light strip.
Ordering
When ordering your MOSFETS make sure that:
- They are triggered by just 3V (Ones that need 5V won't work.)
- The are N-channel type. (or N-MOS)
Complex example
Here is an example of a RemoteSign ESP controlling three color lights strips plus one white light strip as well as a switch input. Each color strip uses three MOSFETS and the monochrome one uses the tenth one. A switch behind a cupboard door is connected to a sensor pin on the RemoteSign ESP and that will trigger the cupboard light to come on like a fluorescent tube when the cupboard is opened, and then fade out the lights after 5 minutes. At night, the three colored lights slowly cycle through the colors of the rainbow independently, providing an everchanging lighting effect.
The small green circuit board takes 12V DC and produces a 3.3V output which is ideal for powering the RemoteSign ESP, and I take the 12 V for all the lights from that supply point. This saved me from having to supply a separate power supply for the processor.
Here one can see the {STATS} in RemoteSign Log
TL;DR;
Buy N-MOS modules that are triggered by 3V and connect as shown.
