Hi, I've read everywhere that VIN must be between 7 to 12 volts to power the uno.
Because it would suited me for space on pin usage I tested using my 5V supply and my project is working.
I checked the supply and it is 5V.
Does anyone have any thoughts suggestions why this should be.
Cheers Roy
Why not do it the correct way and supply 5V to a 5V pin on the Uno ?
I'm not sure why you are on here questioning your incredible luck, you should be out buying lotto tickets.
Where, between what two connections?
Try between gnd and the 5V pin on the UNO.
What hardware do you have connected to the UNO 5V pin?
Thanks.. Tom... 
Because discoveries are made by not doing things the correct way
and
Because it would suited me for space on pin usage .
There is more than one 5V pin on a Uno. Are you using both of them ?
You raised a good point Tom, as I had not checked the voltage on these pins.
The supply is one of these Chinese mains buck converters.
The Uno is running a 2.4 inch touch screen , a DH22, an LED, and a 5V relay which makes it very awkward to measure across any pins, so I connect the buck converter to an LED to give it a load and used a digital meter across the LED. It read 5.05V.
I then used a spare uno just running blink on which I could read the voltage.
It read 4V on the 5V pin, so I'll assume the same is true on my project however the project is running so I must be just lucky.
There is another reason that I connected the supply to the VIN, which I originally forgot to say . This is because I do not know how good these buck converters are at keeping a steady voltage supply and did not want to connect it to a 5V pin and damage the Uno.
I'd had the impression that going via VIN with 5V the uno would not even fire-up let alone run my project.
So your post has been useful in helping me understand what is going on.
Thanks.
You may want to power the relay coil directly from the buck converter 5V output. This could improve the overall reliability by helping prevent the regulator on the Arduino board to drop below your 4V.
Still not my preference, but you are the lucky one...
Hi,
Very lucky, but also your project over time will not be very reliable.
Why can't you measure the 5V on your project with a DMM, you must have access to some points that are powered by the Uno 5V pin.
The hardware relies on a CONSTANT regulated 5V, your UNO is not/cannot regulate the 5V pin in the configuration you have.
Can you PLEASE post some images of your project and a circuit diagram.
The circuit diagram is essential in checking your circuit.
A schematic is worth lots and lots of misguided posts. and that means time.
Tom...
I've made these, principally for having more GNDs, but there's more access to VIN, 5V, and 3V too.
The image does not show the Uno being powered from VIN. When the power expansion board is removed and 5V is applied to VIN the board works, correct?
Who? Me?
Sorry. My error. My apologies.
Thanks Tom.
I will respond. At the moment very busy.
That looks very clever.
Hello, Tom.
I've started with Arduinos only a short time ago and have lots to learn.
The project I've made is a temperature controller to turn on and off my oil filled radiator in an unheated room. I've used DHT22 to detect the temperature. The temperature is set via my touch screen device.
I realise now that my original question was wrong.
I have a 5v buck converter. An SM-PLGO6A, which I know should go to the 5V pin. However these products are so cheap that I wondered how stable they are.
So I think I should have asked if anyone knows the stability of them as I was concerned at blowing up the uno if the SM-PLGO6A is not all that stable.
Thanks for your interest.
Roy
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.