I’ve been chasing some strange ghosts with an Arduino project I’ve been working on.
After experiencing some random and erratic behavior that’s been hard to pin down. I happen to put a volt meter on the board that the Arduino Uno is plugged into (designed by an engineer that is no longer with the company, and I myself am a software guy not a hardware guy), and I measured the voltage at 7.4V.
I’ve read that the Arduino can behave strangely below 7V, but even though my reading shows 7.4 V I bought a 9V regulated power supply and powered the Arduino directly and it seems to have a positive effect in that these random erratic problems we’ve been having seem to disappear when I do that (I say that because I still have to test further since this is a random thing).
Strangely though, whether or not I use my 9V power supply for the 7.4 V source that is on the board the Aduino Uno is plugged into, the pins on the Arduino itself consistently read 5V. So that would indicated that 7.4 vs 9 doesn’t matter? Yet these issues we are having seem to be gone when I power it with 9V.
My next thought was to get a scope and look at the waveform of the 7.4V.
Anyway, I was wondering if anyone has any experience with voltage issues and the Arduino?
The board should have a 5V regulator. Depending on which regulator is used (part number) the drop-out voltage can be as high as 2-3V. So 7.4V may be ok or marginal whereas 9V would be god but just disapates more power (heat) in the regulator.
Do you have an O’scope? If so then look at the regulated 5V at the Atmega processor power pins to see if the voltage is steady or if if has dips. If there are dip then the processor may be pulling excessive power during a certain code operation.
A Voltmeter will average the measurement and not see any short term Voltage drops. These Voltage drops can effect the processor’s proper operation.
If there are dips then check that all the de-coupling Caps on the processor’s power/grounds pins are good (not damaged or missing). Another possibility is that an Output pin is trying to drive too much current so check any external circuit connected.
You’ve given us little to go on. The Arduino Uno has an onboard voltage regulator. Input supply voltages in a reasonable range (7-12 or so volts) will be regulated down to the 5V the onboard components run on. Thus you see the output pins at 5V. If you use a very noisy supply you can “defeat” the regulator and it’s output, while averaging 5V, may have dips that cause the erratic behavior you’ve seen. Look at the 7.4V supply with the scope and the 5V as well and see how far above and below 7.4V it goes (and the result on the 5V regulated Uno voltage). Look again with the 9V supply.
Thanks to both of you for the reply. I apologize for not providing enough info. Been doing software sleuthing for 25 years. Hardware is new to me.
The system I’m trying to hook into already has it’s own existing wired control pad which is driving a 220V high powered motor.
Currently the Arduino and WiFly RV-XV/Wireless SD Shield combo is piggybacking on top of this main controller board.
There is a transformer block on this board which appears to be bringing the 220V down to 24V and then somehow the Arduino is getting 7.4 Volts fed into it.
The guy that implemented the hardware is no longer with the company, and I was able to ask him about this and he said the 7.4V issue I mentioned was not an issue. But my experimental data seems to indicated otherwise.
I was puzzled why if we have 24V coming off of the transformer, and that the arduino can run between 7 and 12V, that we didn’t stay in the middle of that range around 9 or 10. He indicated a heat issue concern as they reason he went with 7.4V.
So from your replies the good news seems to be that perhaps there is something to my concerns. I will see if I can acquire a scope and test these ideas out with the quality of the waveform of the power that is being fed.
Thank you VERY MUCH for replying and giving me some direction. It is very much appreciated.
Do you have the schematics for the board that the Arduino is plugged in to? 7.4V is likely provided from an adjustable regulator, so you can probably change it with a simple resistor change. As mentioned, you want the voltage to be high enough so the 5V regulator reliably puts out 5V and not too much higher since the difference between the input voltage and 5V is dissipated as heat on the Arduino’s regulator.
You also mentioned a WiFly shield. Wireless devices often pull more current while transmitting. If that drags down the 7.4V rail too far, the 5V will drop as well. You may want to add an electrolytic cap from the 7.4V rail to ground to help with this. If you have access to an oscilloscope, you can use it to verify what is really happening.