Hello,
I have a non-5V tolerant wireless module (RFM69HW). I'm using it on a ultrasonic distance transmitter that runs on 5V. The I/O for the ultrasonic distance module (trigger, echo) is also 5V.
The wireless module is on a 3.3V regulator, and the Arduino I/O itself is on 3.3V I/O, so I'm not hurting the wireless module that way. But the ultrasonic sensor is on a separate 5V regulator...so it's sending 5V to the Arduino I/O...is this sending 5V to the wireless module somehow?
I seem to have broken the wireless module. Not sure why.
My understanding is that the voltage you power it at will be the voltage of the digital outputs, and also the voltage of the MOSI pin, for example. If you power the AVR using 3.3V, the MOSI pin will also be 3.3V. That's important for wireless modules that can't tolerate voltages above 3.3V.
But what happens if some other input pin is exposed to 5V, like from an ultrasonic distance sensor? Will the 5V on that input pin somehow put 5V on the MOSI pin?
Well, you can power the ATMEGA328 at various voltage levels. My understanding is that the voltage you power it at will be the voltage of the digital outputs, and also the voltage of the MOSI pin, for example. If you power the AVR using 3.3V, the MOSI pin will also be 3.3V. That's important for wireless modules that can't tolerate voltages above 3.3V.
But what happens if some other input pin is exposed to 5V, like from an ultrasonic distance sensor? Will the 5V on that input pin somehow put 5V on the MOSI pin?
arusr:
The wireless module is on a 3.3V regulator, and the Arduino I/O itself is on 3.3V I/O, so I'm not hurting the wireless module that way. But the ultrasonic sensor is on a separate 5V regulator...so it's sending 5V to the Arduino I/O...is this sending 5V to the wireless module somehow?.
Yes, it could be sending 5V to the module.
Reason: Arduino I/O pins have protection diodes on them. If you apply a voltage higher then Vcc to a pin it will go down the diode into Vcc, possibly raising the voltage coming out of other pins.
You need to put a resistor divider on the outputs of the ultrasonic sensor to drop it to 3.3V.
running outside the specification for a 16MHz clock.
you need to disconnect any 3v3 peripherals when you are uploading code because then the USB runs it off 5V
Could it be that you have fried the TX during upload?
Running the ATMEGA328 at 16MHz and 3.3V hasn't been a problem for the most part. For the Arduino Buono board I'm using this on, I think 3.3V/5V switch works for both the USB power and the AC adapter power...but thanks for pointing that out. I should verify.
fungus:
Yes, it could be sending 5V to the module.
Reason: Arduino I/O pins have protection diodes on them. If you apply a voltage higher then Vcc to a pin it will go down the diode into Vcc, possibly raising the voltage coming out of other pins.
You need to put a resistor divider on the outputs of the ultrasonic sensor to drop it to 3.3V.
That's a good idea. Thanks. It's a quick modification. I'll give it a try and report back.
Running the ATMEGA328 at 16MHz and 3.3V hasn't been a problem for the most part.
Why on earth do you think that manufacturers say these things. It is not for fun. You are operating outside the working spec. The fact that it seems to work now is nether here nor there.
Arduino Buono board
Ah so not a real Arduino then. Just a ropy design.
Running the ATMEGA328 at 16MHz and 3.3V hasn't been a problem for the most part.
Why on earth do you think that manufacturers say these things. It is not for fun. You are operating outside the working spec. The fact that it seems to work now is nether here nor there.
Arduino Buono board
Ah so not a real Arduino then. Just a ropy design.
If I'm not mistaken, the voltage/frequency spec is for the quoted operating temperature, up to 85C. If you don't use it in that hot an environment, you can get away with overclocking it. Ideally, there would be a temperature/frequency/voltage curve to tell you what the xx.xx% reliable operating conditions are for any particular set of dependent variables. That's my guess.
I don't know if the Buono board is inferior in design to the Arduino or not. I'm pretty new to this. But the nice thing about it is that it includes a 3.3/5V switch. Pretty handy. It's on me to use this right and to connect the right voltage components and understand the consequences of putting 5V on a 3.3V system. That's just part of learning. But I don't think a non-real Arduino necessarily translate to a poorly designed Uno.
If I'm not mistaken, the voltage/frequency spec is for the quoted operating temperature, up to 85C.
You are mistaken it is not as easy as that. There are many factors affecting the speed of a circuit and temprature is only one. In fact it is the bottom end that suffers from a pure CMOS operation point of view but that is not the whole story.
There is no data because there is no simple corrilation.
So what makes it a ropy design is not that it is not an official board but the it is designed to operate outside the manafacaturer's specification.
arusr:
If I'm not mistaken, the voltage/frequency spec is for the quoted operating temperature, up to 85C. If you don't use it in that hot an environment, you can get away with overclocking it.
arusr:
If I'm not mistaken, the voltage/frequency spec is for the quoted operating temperature, up to 85C. If you don't use it in that hot an environment, you can get away with overclocking it.
Where does it say that on the datasheet?
Assumption on my part. It doesn't make sense to that the reliability is the same across the entire operating range of operating temperature for the same voltage/frequency combination.
Assumption on my part. It doesn't make sense to that the reliability is the same across the entire operating range of operating temperature for the same voltage/frequency combination.
Yes, but you're just guessing at the answer and going against the advice of the people who actually designed the chip(!)
Is it good practice to guess at whether it will work or not when you're selling product to people for money?