While testing out the 37 sensor kits, I’ve got three of them with different sensors, I have discovered some design shortcomings which might end up in destroying either the sensor or the attached microcontroller (the Arduino board). The issues are with some of the sensors that aren’t sensors in the traditional sense. These are output devices, not input devices, and the problems occur when the device draws too much power from the Arduino’s digital output pin. There are two major issues:
No current limiting resistors on LEDs. An LED basically drops 2 to 3 volts, depending on type, when illuminated. If more voltage is applied the diode effectively will consume more current until either the diode burns out from the heat or the driving circuit, usually the microcontroller, fails from the overload. Current on output pins should be limited to 20mA or less. A resistor in series with the diode will limit the current. I’ve found that Keyestudio always has current limiting resistors on their sensor kit boards, however other brands most often do not and require adding current limiting resistors to the circuits. Unfortunately the instructions frequently do not mention this.
No transistor drivers on high current devices. Some devices, like the buzzers, consume too much current for a digital output pin and need a transistor buffer amplifier (just an NPN transistor and a resistor, nothing fancy) to handle the current. The relay is one such module that does have a transistor buffer on the board, however most buzzers do not. Particularly bad is the “passive buzzer” which is a 16Ω impedance speaker. This basically will look like a short circuit to a digital output pin. A buffer amplifier or a current limiting resistor must be used.
Without the proper precautions, the parts may work for a while, possibly long enough for them to be tested as part of checking out the kit. However if you actually intend to use these devices in projects that you intend to run for long periods of time, you must not use these parts in the way suggested by the kit’s instructions.