Accidently hooked up supply to a GND only wire. :( - Page 1
Forum section: electronics / projects

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:05:51 am
content: Okay, I have the circuit, as described in the schematic below. It's a hall effect switch.The circuit tested works as intended, however, when I disconnected it, and reconnected it, I accidentally hooked up the CNTRL wire to +5 volts (the wire was only intended to be connected to ground or left floating). Now the circuit doesn't work. Magic smoke! But, I didn't see where the smoke was coming from, and have no idea what went bad. What would cause the problem? I need to protect this, on future boards, from this happening by accident again.Any ideas? If I place thishttp://www.mouser.com/ProductDetail/Toshiba/1SS389TL3FD/?qs=sGAEpiMZZMtQ8nqTKtFS%2fEBgKFtUD%252bvpN8ASwV0fsKE%3din series between R4/R6 and CNTRL IN, cathode toward the CNTRL IN, would that fix it? I need a really small diode, no room on the circuit board. This circuit will only see max of 5.25volts, and just what the components on the schematic will use.Thanks in advance for your help.Jason

author: IanB
author_rank: Super Contributor
timestamp: December 15, 2014, 02:25:13 am
content: According to your schematic, it doesn't look to me like connecting CNTRL to VCC would cause any trouble at all. At a guess, I would say you did something else bad, and didn't notice what you did?

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:28:06 am
content: ya, I don't understand it myself, but that is what happened.

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:30:56 am
content: I will hook it up again (another one i have made) and see if supplying 5volts to the cntrl wire fries it again. Hey, it's only a couple bucks wasted each time i do this.better to find the problem, then go on with the way it is.

author: 8086
author_rank: Super Contributor
timestamp: December 15, 2014, 02:31:33 am
content: Yeah, I don't see the problem either.Any visible damage if you look at the ICs?

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:41:38 am
content: Okay, just tried it with another one i had made. Hooking up the cntrl wire to either ground or supply did NOT damage it. I must have done something else to the circuit that damaged it.Maybe I had a solder bridge or something somewhere and didn't notice it. Those small componenets are near impossible to see if a solder bridge happened somehow underneath them.

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:43:53 am
content: I guess from looking at the schematic, the ONLY way to fry the circuit, would be to actually be to hook up the Vcc and GND backwards. I could see how that would damage the hall sensor and the two logic chips.

author: Falcon69
author_rank: Super Contributor
timestamp: December 15, 2014, 02:53:35 am
content: 8086,no visible damage that I could see, it happened so fast. Like I said above, the only thing I could think of, was maybe I had a solder bridge or a hairline piece of metal or something that was touching the gnd and vcc together.But, now that i remember, it was at the other end of the wire i had soldered to the board. I think perhaps maybe I had touched the vcc and gnd wires by accident, when I was plugging them into the breadboard. So, to protect from THAT happening, would that diode i mentioned solve that problem? Or would I need to place a diode across the vcc/gnd with cathode toward ground. Like in this schematic? D3 and R7