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Topic: Power final project via USB (not computer) (Read 725 times) previous topic - next topic

pcguru000

Im hooking up a project on my motorcycle- using a Arduino micro which doesn't have a barrel jack and I'd prefer to not use the Vin/Grnd because I already have a usb hub hooked up on my bike (for charging other devices)

My concern though is- does the USB input have any voltage protection? I tested the voltage on my usb hub and i see it hover between 5 and 6 volts... is that okay or could this damage my Arduino?

Thanks!

Erdin

It will damage the Arduino.

You can apply 5V or 6V to Vin.
The Arduino might run at a lower voltage, but that is almost never a problem. The Micro uses the ATmega32u4 which works at 16MHz at 4.5V.

If the Micro doesn't use a lot of power (like 10 leds) you could measure the 5V voltage pin. It should be very close to 5V if Vin is 5V.

A lower voltage will have influence on the analogRead() if the default voltage reference is used.

The schematic of the Micro is on its page, http://arduino.cc/en/Main/ArduinoBoardMicro

CrossRoads

6V is the Absolute Max begore  damage is likely to occur.  12V is right out!
You can take the 6V and run it thru a couple of 1n4001 type diodes to drop it down to ~5.3, 4.6 kind of range and then bring power in via the USB connector.
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.

pcguru000

So am i better off just running 12v via the Vin input on the board straight from the bike?

I don't mind doing that I guess- just felt it would be more consolidated plugging in ONLY the usb wire.




CrossRoads

Your application, your call.
How clean is the 12V from the bike?
I would be hesitant to use it without some protection from spikes & ripple & stuff.
Perhaps an intermediate switching regulator.
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.

Erdin

At 12V the small voltage regulator has to dissipate the 12-5 = 7V. It might get hot.
If you can't keep your finger on the voltage regulator, it is too hot.
Can you try using 5V at Vin and measuring the +5V output pin of the Arduino ? I don't have a Micro myself to test it.

CrossRoads

5V at Vin is not going to make it thru the regulator too well.
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.

Erdin


5V at Vin is not going to make it thru the regulator too well.

True. But the Micro has no diodes in the Vin path. It uses mosfets. It should be close to 5V if the Vin is 5V.

CrossRoads

Still, Vin goes thru a NCP1117-5
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF
and that need 6.5-7V to make 5V out:

Vin = 7.0 V, Iout = 10 mA, TA = 25 °C
Vin = 6.5 V to 12 V, Iout = 0 mA to 800 mA (Note 4:  NCP1117: Tlow = 0°C , Thigh = 125°C)
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.

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