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Topic: should i use a resistor? (Read 101 times) previous topic - next topic

diy7

Hi,

I am new to electronics. I bought a buzzer from local electronics shop. All it says on its sticker is "27mm 110db 1.5v to 27v DC continuous" . I want to use it with arduino uno, my question is, do i need a resistor to use it with arduino's digital pin? if yes then what value of resistor?

also for pir motion sensor (PIR SENSOR STANDARD MOTION DETECTION MODULE) do i need a resistor ?

Thanks in advance

DVDdoug

#1
Nov 04, 2014, 08:22 pm Last Edit: Nov 04, 2014, 08:25 pm by DVDdoug
You need to know the current (mA).  The Arduino's output pins are rated at 40mA maximum.  Do you have a multimeter?    (Don't measure the current with the buzzer connected to the Arduino, check it connected to the 5V power supply.)

You can try a ~200 Ohm resistor in series and that will protect your Arduino from over-current.   You'll just have to see if it's loud enough with the resistor (or if it makes any sound at all).

If it needs more than 40mA, you'll need a transistor or MOSFET to "boost" the current.

Quote
also for pir motion sensor (PIR SENSOR STANDARD MOTION DETECTION MODULE) do i need a resistor ?
Do you have the specs or datasheet for it?   

LarryD

Quote
Arduino's output pins are rated at 40mA maximum
Don't use more than 20ma per pin.

Partial quote from @Crossroads :
"The limit is 200 mA Absolute Maximum per VCC & Gnd pin, then the current limit per port and per pin.

'328P in a DIP package has 1 VCC pin, thus 200mA limit.
'328P in a surface mount package, thus a 400mA limit.
The Notes in Section 29 show the limits per port, totalling 300mA:

ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET] 304
8271G-AVR-02/2013
Notes: 1. "Max" means the highest value where the pin is guaranteed to be read as low
2. "Min." means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
ATmega48A/PA/88A/PA/168A/PA/328/P:
1] The sum of all IOH, for ports C0 - C5, D0- D4, ADC7, RESET should not exceed 150mA.
2] The sum of all IOH, for ports B0 - B5, D5 - D7, ADC6, XTAL1, XTAL2 should not exceed 150mA.
If IIOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
4. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
ATmega48A/PA/88A/PA/168A/PA/328/P:
1] The sum of all IOL, for ports C0 - C5, ADC7, ADC6 should not exceed 100mA.
2] The sum of all IOL, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 100mA.
3] The sum of all IOL, for ports D0 - D4, RESET should not exceed 100mA."
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.hl
The way you have it in your schematic isn't the same as how you have it wired up!

diy7

Thank you for reply. No i don't have multimeter. But I think I should buy one.

for pir sensor i get these info form sellers website

Communication: Single bit high/low output
Operating temperature: 32 to 122 °F (0 to 50 °C)
Operating voltage:  DC 3.8V - 5V
Static power loss: ≤ 50 uA
Delay time: 30 Secs (0.5~900 Secs is optional)
Blockade time : 0.5s-50s (acquiescently 0 seconds)
Dimensions: 1.27 x 0.96 x 1.0 in (32.2 x 24.3 x 25.4 mm)

Paul__B

Thank you for reply. No i don't have multimeter. But I think I should buy one.
Not "should", must!  You cannot practice electronics without one; simple as that.  A $5 one will do most of the things you will need to do, certainly at this level.  It has limitations, but you need to be doing very involved projects before you need more than that.

Use a 220 ohm resistor and see if the buzzer sounds connected through the resistor to 5V, and guess how much it differers from connecting it directly to the 5V.

But only do this after you have ordered the multimeter.   :D

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