Direct Solder To 9V in

Hello, I just want to confirm something here about if I’m wanting to direct solder my 9v power source directly to the 9V barrel connector on the Arduino Uno.

The model of Arduino I have is in the attachments. From looking at some other posts about direct soldering the 9V power it looks like I would connect something like this:
Lets say this is a back view of the Arduino model I have (Please See Attachments)
the “0” are the solder pads
The _________ are my connection leads

______________ 9V +
|
0 0___________ 9V -
0

Please excuse my poor representation. The Barrel Connector port would be on the right facing towards where I have my power inputs.

Would this be correct for this model of Arduino?

On another Note I have heard that you can directly hook 9V up the the VIN Pin and the GND pins.
Would this also be true for a 9V converted from 12V using a 7809 power regulator?

Well, it's not clear to me what you are indicating with your "text art" but an easier way would be to connect to the Vin and Gnd pins/solder pads, as you have heard. Those are the same connections as on the barrel connector. Also, if you need, for some reason, to actually connect to the barrel connector pads, then use a continuity tester (most Multimeters have this feature -- or just use the lowest Resistance setting), to sort them out by comparing continuity with the Vin and Gnd pads.

And, yes, 9V, converted from 12V can also be used...BUT, the Arduino UNO can take up to 12V on the Vin pin, so why not just connect the 12V supply directly?

ReverseEMF:
Well, it's not clear to me what you are indicating with your "text art" but an easier way would be to connect to the Vin and Gnd pins/solder pads, as you have heard. Those are the same connections as on the barrel connector. Also, if you need, for some reason, to actually connect to the barrel connector pads, then use a continuity tester (most Multimeters have this feature -- or just use the lowest Resistance setting), to sort them out by comparing continuity with the Vin and Gnd pads.

And, yes, 9V, converted from 12V can also be used...BUT, the Arduino UNO can take up to 12V on the Vin pin, so why not just connect the 12V supply directly?

Ah OK, thanks, Yeah I had not really realize that I could have just connected 12V directly :slight_smile:
ha ha and I went to the trouble of creating a 12V to 9V step down voltage regulator I rigged up right on the little custom shield I created lol Go figure... Oh well, I guess i'll just dump it's 9V output into the VIN & ground pins, no harm no foul I guess??

Don't forget, the greater the voltage the 5V regulator has to drop, the lesser the current it can output without overheating.
7V in, 5V out, 2V dropped * 800 mA = 1.6 Watts dissipated = OK.
12 " " " 7V " " " " = 5.6 " " = Overheat & shutdown.
" " " " " " " 230 " = 1.6 " " = OK.

Correct, but I doubt that the regulator of an Uno can dissipate 1.6watt long term.
More like <=1watt for the Uno, and <=1.5watt for a Mega (with larger D-pak regulator).
Depends ofcourse also on ambient temp and enclosure.
Leo…

If you went through the bother of bucking, why didn't you just go down to 5v?
Or why not use a 5v PSU in the first place?
If this is automotive '12v', then there are a few more things to consider.

INTP:
If you went through the bother of bucking, why didn't you just go down to 5v?
Or why not use a 5v PSU in the first place?
If this is automotive '12v', then there are a few more things to consider.

Yes it's an Automotive 12V that is being stepped down to 9V.
This particular Arduino project is just for a Surveillance Mode module that has 3 PIR Sensors attached and 8 red LEDs. that for from a chaser pattern to an middle outwards chaser pattern when Human motion is detected, a signal is then sent out that we catch with the Arduino Mega.

I made another one just like it only I connected right into the 9V barely connector after stepping down the 12V
The Car 12V gets activated from the Arduino Mega that turns on a relay switching the 12V to turn on the surveillance mode module.
I've had the original one running for a long time now and it appears to work without any trouble, the LM 7809 barely even gets warm, even on a pretty hot day.... mind you that was outside of the project box I have it enclosed in, but installed I've tested it on a hot day out in the garage and it seems to be working with no troubles.

Knightriderguy:
Yes it's an Automotive 12V that is being stepped down to 9V.

That, my fellow, is a horse of a different gate! Definitely use the 9V regulator, 'cuz [and this has ignited mass debate in the past] car voltage is not only not a stable "12V" [can be as high as 14V], it's not all that clean!
BUT
that's my knowledge of cars of yester-year. I'm a bit out of touch on that subject -- and I currently own [and drive] a Hybird, so any testing on my car, may not be representative. So, I will defer to my colleges, for "clarification" :smiley:

Yeah . . . . being an automotive environment was a big detail to leave out.

But your distilled question of simply 'can I solder 9V to the pins that are electrically identical to the barrel jack pins' has been answered as 'yes'.

The rest of this talk is just advice and suggestions for optimizations or elegance/efficiency improvements.

Where are you pulling 12V from inside of your car? Direct from battery? Cig lighter accessory socket? In-cabin power distro block? Have fuses in place? What vibration isolating measures do you have in place for your components?