Capacitors are for the power line, not in parallel with the flyback diode.
wvmarle:
(I don't know the failure mode of a zener)
Overvolt them backward and they explode like cheap firecrackers.
I've seen it done for kicks by someone who got a chunk of a reel at salvage price.
Hi
I have it working nicely now.
Running 7.2V on the power socket input and using a direct wire to the +12V for the flyback diode.
The power input transistor is staying cool.
I do not know which of these changes is allowing to run well. I suspect the 12V wire. Oddly enough, I do NOT want to kill another Uno board to find out.
Thank you for your comments and suggestions.
You need to be careful what voltages you put on the pins, including the VCC pins. 5.5V is absolute max for many Arduinos but for some, 3.7V is max. They run at nominal 5V and 3.3V respectively.
Every Arduino has the specs shown on the Arduino website. At the top of your screen you should see a green bar with words and symbols on it. Click PRODUCTS and you can check out any Arduino and find out many details useful to not burning them up.
If you spend a few bucks on some ATmega328P-PU's (a bit over $2 ea here) and breadboard parts, you can experiment on stand-alone chips without endangering your dev board.
Hi
I have been able to confirm that the header pin Vin, connects directly to pin 3 of the regulator (AMS1117), while the power connector input goes through a diode.
At the least this means no polarity protection when Vin is used to supply power.
If you wish to check, follow the tracks. I used images from
looking at images 7 and 8.
I think this means that the regulator had significantly more than 12V coming in when the solenoid turned off.
It also means my current 7 volt regulator might ultimately fail for the same reason
Grabcad ?
If you want a schematic diagram of the (official) Uno, look here: https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
Confirmed by Arduino under the Documentation tab here:
https://store.arduino.cc/usa/arduino-uno-rev3
The power pins are as follows:
Vin. The input voltage to the Arduino/Genuino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
GND. Ground pins.
IOREF. This pin on the Arduino/Genuino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs to work with the 5V or 3.3V.
GoForSmoke:
If you spend a few bucks on some ATmega328P-PU's (a bit over $2 ea here) and breadboard parts, you can experiment on stand-alone chips without endangering your dev board.
I thought that was supposed to go the other way around... use development boards for the ease of experimenting on them, and not risking to endanger the much harder to build (and modify) prototypes. Or maybe I completely miss the point of development boards, that's entirely possible.
iborg:
I think this means that the regulator had significantly more than 12V coming in when the solenoid turned off.
Why?
It also means my current 7 volt regulator might ultimately fail for the same reason
Seeing as how the Uno has a 5 volt regulator I wouldn't worry about the non-existent 7 or 12 volt regulators.
When you ran 12V through the regulator to do everything, it had to drop 7V x the total current into heat with your external component current use in that total.
When you ran 12V directly to the external component, that much load was taken off the poor little 7805 regulator.
When you dropped the 12V going into the regulator to 7.2V, that made a big increase in the efficiency the regulator is operating at, 30% loss as opposed to 58% loss with matching decrease in heat.
The Arduino site used to advise not drawing more than 200mA through an Uno. It may still somewhere but I don't see it on the product page any more.
Also maybe you can explain how a linear regulator dissipates WATTS of heat while only losing VOLTS.
My comment
If you spend a few bucks on some ATmega328P-PU's (a bit over $2 ea here) and breadboard parts, you can experiment on stand-alone chips without endangering your dev board.
wvmarle:
I thought that was supposed to go the other way around... use development boards for the ease of experimenting on them, and not risking to endanger the much harder to build (and modify) prototypes. Or maybe I completely miss the point of development boards, that's entirely possible.
Or you completely miss the difference between "the much harder to build (and modify) prototypes" and a breadboard duino.
If you want to bring in other circuitry then consider it would have to be wired to the Uno or the breadboard and the chance to lose whatever gets lost either way.
I can highly recommend Nick Gammons breadboard AVR tutorial, you can DIY a duino really cheap and get a start on using other AVR's like the 1284P. You don't need the breadboard if you can solder, not much is actually required to run an AVR.
When I need external 5V parts that draw a substantial amount of current, I mostly use a buck converter, e.g. an LM2596. It has a thermal shutdown and current-limit protection, can handle up to 3A, input voltages up to 40V and it's much more efficient than a linear regulator.
Just connect the solenoid and the LM2596 to your 12V supply, and connect the output of the LM2596 to the 5V pin of the Arduino and your 5V sensors.
The 5V regular on my Uno has been working for years, and I've often used a 12V adapter, but never with heavy 5V loads.
wvmarle:
I thought that was supposed to go the other way around... use development boards for the ease of experimenting on them, and not risking to endanger the much harder to build (and modify) prototypes. Or maybe I completely miss the point of development boards, that's entirely possible.
I prefer prototyping on a (large) breadboard, and it's much easier to just pop in an ATmega/ATtiny than to have a separate Arduino connected with wires. It always gets in the way and the wires come loose ...
Just an ATmega + some bypassing caps, a crystal, a capacitor and diode for the reset circuit, and an FT232 are all you need. Or if it's an ATtiny without a bootloader, I just use a USBasp.
Pieter
You don't even need the crystal and caps if you don't mind running 8MHz or slower (and gain 2 pins).
You don't need the reset circuit if you re-purpose (and gain for use) the reset pin (kill power to reset).
I count power, ground and a bypass cap as minimum though without any IO AVR's are not real exciting.