Contents
How is an input protected in a microcontroller?
Consult the microcontroller data sheet before putting RC networks on these types of microcontroller inputs. Figure 10-3 shows an input protected with a zener diode. A zener diode acts like a regular diode with one exception. If the reverse voltage reaches a certain point, the diode will start to conduct.
Can a microcontroller safely connect to an I / O device?
Many I/O devices consume a lot of current (> 100mA), which most microcontrollers cannot supply safely and when they try to supply this amount of current they will often break.
What happens when a microcontroller outputs a 0?
When the microcontroller (connected to “IN”), outputs a 1 then the transistor Q1 turns on. This turns on relay RL1 and the result is the lamp (R2), turning on. If the microcontroller outputs a 0 then the transistor Q1 turns off which disables the relay and therefore the lamp turns off.
How is a microcontroller connected to a transistor?
This simple circuit is handy for controlling high powered LEDs by microcontrollers where the microcontroller output is connected to “IN”. When the microcontroller outputs a 0 then the transistor Q1 turns off and so does the LED D1. When the microcontroller outputs a 1 then the transistor turns on and therefore D1 also turns on.
Why does a microcontroller need a 100R resistor?
The 100R resistor is used to prevent too much current flowing when the Zener diode clamps the input voltage. Inputs and outputs of microcontrollers may sometimes need to be protected from too much current flow.
How to protect ADC inputs from overvoltage?
A common issue that arises when designing an ADC circuit is how to protect the ADC inputs from overvoltage. The protection of ADC inputs has many scenarios and potential solutions. ADCs from all vendors have similar needs in this respect.
What kind of resistor do I need for a microcontroller input circuit?
A resistor of a couple of hundred ohms and a capacitor of .01 or .1 microfarads will give reasonable protection to the input. An RC circuit is also known as a low pass filter.
How is an input protected with a Zener diode?
Figure 10-3 shows an input protected with a zener diode. A zener diode acts like a regular diode with one exception. If the reverse voltage reaches a certain point, the diode will start to conduct. In combination with R to limit the current and drop the excess voltage, the voltage seen by the input will never exceed the zener voltage, Vz.
Which is the best voltage for a microcontroller?
For applications with noisy electrical environments, it is usually best to run the microcontroller near the high end of the allowable Vcc range. On the other hand, running at higher supply voltages will mean more power consumption. Those are the kind of tradeoffs that you will need to make as a circuit designer.
What does a voltage near VCC read as?
A pin with a voltage near Vcc (or Vdd) will read as a logic 1. As a first approximation, any input less than half of Vcc will read as a 0, and any input over Vcc/2 will read as a 1. There is a voltage band however, right around Vcc/2, where there is no guarantee what state will be read. Refer to Figure 5-1.
What happens if the input goes above Vcc?
You don’t want to subject inputs to voltages above Vcc or you can damage the IC. For that matter, you do not want the input to go below ground (0V). That can cause the internal circuitry in the IC to latch up, and possibly draw excessive current and damage or destroy the IC.