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Topic: Arduino uno I/O pins output are 4.2v not 5v (Read 1 time) previous topic - next topic

zhirantaha

i make one pin output and take out by a jumper wire then measure it by mutlimeter.
i connect them relay and they can't swith the relay but when i connect directly the relay to 5+ it switch.
before i did this and there was no problem//

retrolefty


i make one pin output and take out by a jumper wire then measure it by mutlimeter.
i connect them relay and they can't swith the relay but when i connect directly the relay to 5+ it switch.
before i did this and there was no problem//


Can you just answer my questions, one at a time that I listed below?

Lefty

CrossRoads

4.2 is within spec:
See Section 29
VOH Output High Voltage(3),  IOH = -20 mA, VCC = 5V:  4.2V

Note (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.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

michinyon

You would be pushing your luck to have an arduino digital output drive a relay,  unless it
is some kind of special relay with a very low input requirement.

Make a circuit with a transistor to drive the relay.

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