Is this Safe for the UNO32

Created Thu, 09 Feb 2012 08:08:11 +0000 by submission

submission

Thu, 09 Feb 2012 08:08:11 +0000

Hello all, just working on a project and somthing got me concerned ..... Here is a link to show what Im doing click on the attachments to see the pictures , also if you scoll down a little there is an MPIDE sketch there as well .

All seems to be working well .... No smoking yet :|

Im using the UNO32 to control a cctv cameras settings . The Camera uses 5 surface mount Normally Open pushbutton switches...the switches have 2 pairs of contacts and as usual these have been connected in parallel . The pads are connected to the cameras GROUND (0vdc) . The cameras internals use 3.3vdc . I soldered a wire to one of each pads contacts ( the one thats not Grounded )

I ran a Ground from the cameras caseing to the UNOs ( PIN 14 ) , then conected the other 5 wires to 5 of the UNOs PWM s .

I set all the PWMs to "OUTPUT" and to "HIGH"

To make this work I switch one of the PWMs Digitalwrite to "LOW" , delay( 15 ) , then switch the PWM back to "HIGH".

What concerns me is this..... (1) Both the UNO and Camera are using different power supplies. The UNO is using USB power / while the camera is using a "Clean" 12vdc , though the internals are still regulated down to 3.3vdc . (2) When Digitalwrite on the UNO32 is set "HIGH" it outputs 3.3vdc

Im I taking a risk here of burning somthing out

I viewed the wiring of this like lighting an LED that has one side always hot ( 3.3 vdc ) then using the PWM to conect the Gnd , then of course when the switch is set HIGH again , your sending 3.3vdc to both sides of the LED ..... so whats the harm ..... ?????? I don't know ....Thats why Im here .

Thanks for any help or advice you can offer .

Kyril

KeithV

Thu, 09 Feb 2012 17:48:04 +0000

Take my response at your own risk... I take no responsibility for my answer other than to explain what I (think) I know :?

Pay attention to your grounds and you will be okay; usually. Unless somebody did something stupid. Ultimately ground will be ground and that means it will be at the potential of the ground wire in your house (the bare wire, not the white wire which is neutral and can be up to 5v off; and a LOT of current could flow if you short neutal to ground).

Most transformer type power supplies will pick 1 side of the secondary (or center tap) as ground, since the secondary is completely isolated, either side can be picked, but once picked and tied to ground, that side is ground. Some transformer types (2-wire) don't specifically pick a ground but in theory need to be physically isolated to prevent human shock; low voltage is typically not a problem.

Switching power supplies are suppose to isolate the output, but sometimes there is a side that must be ground. If done right it is just fine. Again good design will have a single point in the supply that will tie neutral (signal zero) to ground (the ground in your house; not to be confused with neutral).

So if everyone has done their job; you should be fine :-) You can check this with a simple voltmeter, check to see if the "round" part of the 3-prong part of a plug in your house has low resistance to what you think should be ground on your design. First check to see if there is a voltage difference, if there is any voltage (say over a volt; but is usually in the millivolt range), there is a problem. If the voltage is effectively zero, then check the ohms, it should be low, like under a 100 ohms; there will be some wire resistance, so it won't be zero. If there is no voltage and high impedance on both what you think to be neutral and hot, your output is probably floating and most likely isolated. This is the worst case, but you can probably just pick what you think to be neutal and at a single point, tie it to ground.

Having said this, some low voltage/current devices do not tie thier neutral to ground, they let neutral float. This is more typically in coil type power supplies. However, if their neutral is floating, it still should be safe to tie what you think neutral is to ground.

Short answer, if you haven't blown anything up by now, your grounds are probabably okay. My concern would be more about exceeding 3.3-5v by mistake somewhere; and blowing the input protection zeners. Remember, static can kill those zeners as well, so make sure the grounds are tied together before hooking up the inputs. And be real careful about any testing, get your wires mixed up and you will probably blow your ohm meter. Order of checking should be: do an AC voltage check, then a DC voltage check, and then if significantly close to zero voltage, do your impedance check.

Good Luck, and remember.... I know nothing!

submission

Thu, 09 Feb 2012 18:54:57 +0000

Thanks KeithV ,

In another way that I viewed this , its like the video camera is another breakout board ..... like my Big Easy Drivers .... one side of the driver board uses 18vdc to power the motors , the other is powered by the UNO32s USB ( dir,step,etc ) .. I have the 3.3 jumper tied on the Drivers .... all grounds between both are tied together ..... Not a single problum .... no overheating , nothing .

Im prity sure I got it rite , its just with this electronic stuff , one mistake and ... Poooof .

Kyril