Here's a simple visual flag that can be used to send a message in code, letting you know if something is available or not (green, red). Just combine the coding beforehand and then use the device. This is very simple assembly, powered by common batteries that will have excellent duration given the low consumption. In figure 1 we have the complete diagram of the apparatus.
In figure 2 we show the welding of the LEDs on a small terminal bridge. The assembly should be installed in a small plastic box or other material.
The R1 resistor is not critical and values between 220 ohms and 1 k ohms can be used. The LEDs can also be of other colors and there is the option to add a third yellow LED.
Material list
LED1 - Common red LED
LED2 - Common yellow LED
S1 and S2 - Pressure switches or single switches
R1- 220 ohms x 1/8 W - resistor - red, red, brown
B1- 3 V - 2 small batteries
Miscellaneous: battery holder, terminal bridge, wires, solder, mounting box, etc.
