I am a CS guy getting started with Arduino. This is probably a very basic electronics question but from going over the arduino tutorials everything is connected to the arduino with a resistor.
Well since i am following the tutorials i know what type of resistor i should use but what i do not know is why i should use one? and What type of resistor to pick i am to do something which is not covered in a tutorial.
The resistor simply serves to limit the current into or out of a pin in case something goes awry. If your AVR decides to output high on a pin that something else wants low (or vice-versa), large, damaging currents can occur if not limited by some resistance. The current limit for AVRs is about 20 milliamps, and given that the voltages are usually 5V, something larger than 250 ohms "would work".
To give a margin of safety, 1-10k is a great choice; for digital signals it seldom matters unless you're into very high-speed applications (beyond the AVRs capability anyways). For analog inputs, a similar resistor would also be advisable, as the amount of current the ADC takes to sample is negligible when your resistor is in the few kilo-ohm range.
The underlying principle that you want to learn is Ohm's Law, which describes the relationship between voltage, resistance, and current in a circuit.
Resistors are used to
limit current,
devide voltage
protect against over voltage
pull-up, pull down
current to voltage conversion
etc ...
1) limit output current, the absolute max current per IO is 40mA, a typical LED works on ±2V 20mA.
the resistance value can by calculated by (5V - 2V)/(0.02A)=150Ω usually a 220Ω resistor is used, because: it consumes less power, there doesn't flow 20 milliamps, and there is no notable difference in emitted light.
2) if you have a analog voltage that variates between 0 and 10 Volts, you 'll need a voltage divider of 1/2. pick by example z2 10k and calculate z1 by 10k*(Vin,max/5V -1). take a value of resistance higher than the original calculated. and recalculate the new Vout.
3) place a resistor of 10k in series between the analog input of the arduino and the 'to measure voltage'
3) if you have to measure a analog current, you place a resistor to ground and the analog input, calculate the resistor by Z=5V/amps.
4) if you connect a button to the arduino, you 'll need to place a pull up or a pull down resistor. if you 're not using a resistor, the input is floating and can take any value (high or low). or you can enable the internal weak pull up. by pinMode(xx,INPUT); digitalWrite(xx,HIGH);. and disabeling by digitalWrite(xx,LOW); by default the pull-up is disabled.
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Im currently trying to get an electric signal from arduino, its 5v and 1amp that i get from a powersupply.
I want to input that signal into an arduino pin, lets say pin 4.
The main powersource from my arduino is via usb, but the 5v signal is from an external device.
I just want to know the number of time that signal became active, like a switch.
As far as i know arduino can take only .04amp from 5v.
Is there anyway i can reduce the current?
Anyway to obtain the value of a resistor to make it less dangerous for my arduino?
Your question is a very common application for Arduino!
You can give your Arduino some additional protection by placing a 10kOhm resistor between the Arduino analog pin you wish to use and the positive voltage output of the power supply.
If you're worried that the voltage could increase above 5V, you can protect your arduino with a simple voltage divider using two resistors. There's a detailed tutorial for this approach here: https://startingelectronics.org/articles/arduino/measuring-voltage-with-arduino/ Here's a simplified circuit diagram with a voltage divider that reduces voltage 11 fold - making voltages up to 55V safe to measure (where the battery could be replaced by your power supply):
For your code, you can use analogread() to read the voltage of the pin. If you wired it correctly, it should return near 0 when the powersupply is at 0, and 1026 or thereabouts if it is at 5v (or whatever the maximum value your voltage divider is designed for). Here is an example to get you started :
https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/
If you need any support with your code to count the number of times the voltage goes high, post that as a separate question along with the code you have so far.
I am fairly new to programming MCU. I have an ATtiny2313 and the datasheet came with a layout of how the pins are configured; however, finding pin 1, since the mcu is a square, is tough for me. I share the images of the diagram and the actual unit. Maybe I am overthinking the issue? Further reading materials are also greatly appreciated.
This is the datasheets diagram
This is the actual unit
Check the Packaging information section at the end of datasheet. There are physical properties of packages described including any marking to identify pin 1.
In some situations (some really small ICs) it can be hard to identify right pin 1 marking. In production, one simply rely on orientation of chip in the tape, but for populating boards by hand, little trick can come handy anytime you are not sure, you have identified pin 1 correctly.
In virtually any IC, there are ESD protection diodes from GND to any IO pin and prom IO pin to power rail. So, if you put a multimeter in diode measuring mode, you should see a drop about 700 mV (actual value can vary) when the positive probe is touching a ground pin and the negative probe any data pin, or when the negative probe is touching a positive voltage rail pin and the positive probe any IO pin. It is not 100 % fail-proof way, but really good and useful hint.
I have a device running off a different power supply, that I'm trying to talk to serially, it has TX and RX lines, GND and 2.7+ line, its quite grunty so It has its own PS.
I'm getting some odd results at the moment, so wondering if I need to use a common GND between the Arduino GND and the PS GND and the device GND.
Does serial require a common voltage reference point?
Its a mega 2560 R3
All signals require a reference voltage. Ground is what provides this reference for single-ended signals such as those used by a UART.
UART signals are composed of low-level and high-level signals.
The receptor, at the other end, to be able to understand your UART signal, must be aware of what is that low-level and high-level signals.
So you must put your UART GND to the GND of the receptor, and the high-level voltage must correspond to the TTL input level of your receptor.
For example, if the high-level of your UART is 2.7v, and your receptor input-level is 5v, you could encounter bad level detections sometime, because 2.7v could be detected as a low-level input.
For the low-level inputs, this is no problem because 0v is always 0v.
Sorry but... didn't you break your 2.7V device? Besides using a common ground, like Ignacio pointed out, when you have to interface something to something else you should ALWAYS check what are the correct voltage levels expected.
So did you check that the high voltage levels and low voltage levels are fulfilled? I think not. Because:
Arduino Uno (i just have the 328P datasheet on hand, so i'll use this) has an Atmega328P powered at 5V. The datasheet says that the Vih parameter (the minimum voltage sensed as a "high" value) is 0.6Vcc, which means 3V. So if you send him a 2.7V signal.... You are doing something wrong.
The 2.7V device has probably an absolute maximum voltage allowed on any pin of Vcc+0.3V. This means that the maximum voltage for each pin is 3V; if you go above this current starts flowing through the protection diode and... you blow your device. Now you are giving it 5V, so.... Puff...
If the above criteria are not fulfilled you have to put between the two circuits something. Which is
a resistor divider if you have to make the voltage lower (just two resistors) and a couple of transistors to make it higher
Opto-isolators (and you can keep the grounds separated)
Voltage translators (such as TXS0102)
other...
I know this sounds a bit funny :). But I am trying to eliminate possibilities:
On the Arduino Uno I have attached an interrupt triggered on HIGH to a routine which only increments a volatile defined long counter. This counter is displayed on an LCD screen.
If I connect a pulse generator with a frequency of 1 Hz at TTL levels, I would expect the counter to increase with about 1 per second. However this is not the case.
As the frequency is 1 Hz (duty cycle 50%) could it be possible that once the counter is incremented the IRS is exited (and clears the interrupt flag) BUT: the INT0 level is still HIGH so the ISR would be called again? At 1 Hz 50% duty, the HIGH would stay for 500 ms and at 16 mHz...
The processor at the heart of any Arduino has two different kinds of interrupts: “external”, and “pin change”. There are only two external interrupt pins on the ATmega168/328 (ie, in the Arduino Uno/Nano/Duemilanove), INT0 and INT1, and they are mapped to Arduino pins 2 and 3. These interrupts can be set to trigger on RISING or FALLING signal edges, or on low level. The triggers are interpreted by hardware, and the interrupt is very fast. The Arduino Mega has a few more external interrupt pins available.
So as commented: It triggers on an edge!
See more details on the Arduino Playground web page.
Two electrical reasons can explain why interrupt does not function as you need.
1- The pulse generator output and MCU input can have an impedance mismatch, which can cause ringing on the waveform edges. For example, if your function generator has a 50 ohm output capable of generating high frequencies you might see a problem driving a high impedance input like the Arduino at low frequency.
The name "pulse generator" makes me think this is a 50 ohm out device intended to make very short pulses with sharp edges. In such a case, you add a terminating resistor at the destination (load) to match the impedance of the source (pulse generator). For a 50 ohm output, 47 ohm would be close enough. If the output is 100 kohm, then place a matching resistor at the Arduino.
2- Just the opposite, the generator waveform edges may be so slow that the voltage passes through TTL 0 to 1 transition multiple times. If you have noise on your signal input, a slow edge could be causing multiple triggers. For example, if you are picking up some 60 Hz ripple from a power supply and grounding issues, your square wave edges won't be as square as you think.
In such cases hysteresis is a solution. There are many ways to de-glitch (debounce) in code. There is no answer that is right for all problems. A simple example would be that the ISR you require that the input reads high twice in a row for the edge to be accepted.
I have tried measuring the analog pin value using the provided standard sketch in the Arduino IDE. However even when there is no connection to the pin, it prints out random values. Is there anything that has to be taken care of?
I have a FSR sensor connected from 5V+ to analog pin 0
No connection giving you random value is completely expected. The pin is floating, and may or may not have a charge on it at any time, giving random values.
Attach the analog input to ground - it should return a number approaching zero (within the accuracy and noise of the ADC).
You have to use "Pull-up" or "Pull-down" resistor. Read here about this circuit: http://www.ladyada.net/learn/arduino/lesson5.html
Providing a path of higher resistance to ground ensures that when that portion of the circuit is open, the static electricity remaining in the portion connected to the pin gets grounded. It also splits the voltage between both paths to allow you to properly throttle the voltage to the pin.
The same problem arise to me ,
What you have to do is change the" Serial.begin(9600);"
To "Serial.beigin(115200);
Now it is showing exact zeroes without any input source.