Typical GPIO pins can draw up to a few mA: for example Arduino MKR pins draw up to 7 mA, whereas Pycom boards up to 12 mA and recommended not to exceed 6 mA (, ). You have a sensor that draws more current than a GPIO pin can sink.If no special care is taken, this will result in continuous current flow, thus high power consumption, although you probably need to activate the circuit a few times per hour or even once per day. The voltage divider is connected to a GPIO pin of the micro-controller. One well-known example is the simple resistor divider which is added at points where the voltage level (e.g. (always keep in mind that low power consumption is of utmost importance for IoT devices). You have placed a sensing circuit at one or more points of your board and you need to avoid energy consumption during idle or deep sleep periods.But, in practice there are many cases and applications where you need a driving circuit based on a transistor switch. For many applications you might not need a transistor at all and you are ready to go. So, you just got your IoT modules and some sensors and you are eager to prepare a first working prototype. In the remainder of the blog post we will assume the switching operation of the transistors, which will be explained through an easy example later on. The above features combined with their smallest manufacturing size makes FETs far more popular, though they are more expensive. FETs have significantly higher impedance, hence they practically draw negligible current. How do BJT and FET differ? In many ways: BJTs are current-controlled while FETs are voltage-controlled. By controlling the voltage or the current of one pair of terminals we can control the current flow in another pair, so in practice “open” or “close” a circuit (in other words “switch”), and not only that, but also we can provide for larger current at the output (in other words “amplify”). They are used for either amplifying or switching signals. Transistors are in essence, electronic elements with 3 terminals, the Base, Collector, Emitter for the first type, called BJTs, and Gate, Source, Drain for the second type, called FETs. There are some excellent introductory and not-so introductory tutorials out there for one to become a “master” of transistor, such as and, so here we just keep it to “high-level”. These modules combine the benefits of well-known ESP-32 and Arduino modules and embedded radio modems for WiFi, LoRaWAN and NB-IoT connectivity, offering an all-in-one solution from sensing to cloud.īefore delving into the details of putting transistor switches in IoT prototypes, a non-electronics expert may wonder what is a transistor, what types are out there, and what exactly means using a transistor as a switch. We will focus on two popular micro-controller families, Pycom and Arduino MKR boards. The purpose of this post is to highlight the multi-fold benefits of using transistor switches in an IoT prototype circuit and demonstrate how to use them through a simple but practical example application. One of the first non-trivial issues that a newcomer into IoT hardware design probably has to deal with, is the use of transistor switches.
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