LEDs are very easy to connect, but there are some basic rules that need to be followed:
- LEDs are sensitive to polarity
- LEDs need a series resistor to prevent them from burning out
- RemoteSign ESP can switch either the positive or negative side of each circuit. You must ensure that you set the RemoteSign ESP output pins to switch either positive or negative to match your LED circuit. This setting is part of the {DCH} command that defines the channel driving the LEDs, such as monochrome lights, color light, signals, traffic lights, or animations.
The output voltage of RemoteSign ESP pins is 3.3 Volts DC.
Each output pin can supply up to 12mA of positive current, or up to 20mA of ground/negative sink.
You should use a 120 Ohm (or higher) resistor for each LED, which will limit the current to 11mA.
By default, RemoteSign ESP output pins will supply positive 3.3V and this can be connected to an LED and resistor and the GND pin as follows:
The side of the LED that must be connected to negative is the shorter leg or the end of the LED with a dot or line. In this case the pin D4 is positive and the G (ground) is negative. The resistor can be before or after the LED.
If you wish to switch the negative side of the circuit, invert the pin logic in the {DCH} command that defines the channel. Here is the screen in RemoteSign Sequencer for defining a monochrome light channel:
and now you can wire the negative side of LED to that pin and the positive side to the 3V3 pin:
The 3V3 pin can supply up to 600mA of positive current at 3.3V.
Note, if you are looking for an additional ground connection (up to 20mA), you can use an unused pin by defining it as a monochrome light and leaving the light off. Be aware that D3, D4, RX, D9 & D0 are all high during boot up. Note also that pin D8 must not be HIGH when the device is booting, making it a poor choice for inversion.
The positive voltage output of a pin is 3.3V and that is only enough voltage to drive one LED.
Placing two LEDs in series would not work, but one can place two LEDs in parallel if switching the negative side, as it can handle 20mA of drain. For example:
Advanced note
If you understand the calculation of the series resistor, you could drive two LEDs using the 5V source and use a pin to switch the drain. For example, if you have two LEDs with a forward Voltage (Vf) of 2.0V, you could connect them in series with a 100 Ohm resistor to the 5V pin and use a pin to switch the circuit to ground. Do not exceed 20mA of drain (negative) on a GPIO pin. Do not allow more than 3.3V of residual voltage to get to the pin. Remember to invert the pin logic, circuits switched on the negative side will be on when the pin is LOW, and off when the pin is HIGH. Note that you can only use the 5V pin of the smaller WeMos D1 mini RemoteSign ESP modules and not the VIN pin of the larger LoLin style modules. Note also, that white or blue LEDs typically have a forward voltage of 3V each so they might not work in series with just 5V.
Connecting signals
Connecting LED signals is essentially no different to connecting other LEDs
Here is the {DCH} screen for defining a signal with 4 lights and two aspects (in this case, a German distance signal). To handle a signal with a common positive wire, the "Invert pin logic" checkbox has been selected.
If the signal has been designed for higher voltages, it may have much larger resistors. If it is too dim, replace the existing resistors with smaller ones.
Here is how one would connect a 5 wire (4 lights plus a common) signal as defined above.
